diff --git a/.ci/scripts/test_export_data_command.sh b/.ci/scripts/test_export_data_command.sh
index ab96387a0aef..224cae921658 100755
--- a/.ci/scripts/test_export_data_command.sh
+++ b/.ci/scripts/test_export_data_command.sh
@@ -21,7 +21,7 @@ python -m synapse.app.homeserver --generate-keys -c .ci/sqlite-config.yaml
 echo "--- Prepare test database"
 
 # Make sure the SQLite3 database is using the latest schema and has no pending background update.
-scripts/update_synapse_database --database-config .ci/sqlite-config.yaml --run-background-updates
+update_synapse_database --database-config .ci/sqlite-config.yaml --run-background-updates
 
 # Run the export-data command on the sqlite test database
 python -m synapse.app.admin_cmd -c .ci/sqlite-config.yaml  export-data @anon-20191002_181700-832:localhost:8800 \
@@ -41,7 +41,7 @@ fi
 
 # Port the SQLite databse to postgres so we can check command works against postgres
 echo "+++ Port SQLite3 databse to postgres"
-scripts/synapse_port_db --sqlite-database .ci/test_db.db --postgres-config .ci/postgres-config.yaml
+synapse_port_db --sqlite-database .ci/test_db.db --postgres-config .ci/postgres-config.yaml
 
 # Run the export-data command on postgres database
 python -m synapse.app.admin_cmd -c .ci/postgres-config.yaml  export-data @anon-20191002_181700-832:localhost:8800 \
diff --git a/.ci/scripts/test_synapse_port_db.sh b/.ci/scripts/test_synapse_port_db.sh
index 797904e64ca5..91bd966f32bd 100755
--- a/.ci/scripts/test_synapse_port_db.sh
+++ b/.ci/scripts/test_synapse_port_db.sh
@@ -25,17 +25,19 @@ python -m synapse.app.homeserver --generate-keys -c .ci/sqlite-config.yaml
 echo "--- Prepare test database"
 
 # Make sure the SQLite3 database is using the latest schema and has no pending background update.
-scripts/update_synapse_database --database-config .ci/sqlite-config.yaml --run-background-updates
+update_synapse_database --database-config .ci/sqlite-config.yaml --run-background-updates
 
 # Create the PostgreSQL database.
 .ci/scripts/postgres_exec.py "CREATE DATABASE synapse"
 
 echo "+++ Run synapse_port_db against test database"
-coverage run scripts/synapse_port_db --sqlite-database .ci/test_db.db --postgres-config .ci/postgres-config.yaml
+# TODO: this invocation of synapse_port_db (and others below) used to be prepended with `coverage run`,
+# but coverage seems unable to find the entrypoints installed by `pip install -e .`.
+synapse_port_db --sqlite-database .ci/test_db.db --postgres-config .ci/postgres-config.yaml
 
 # We should be able to run twice against the same database.
 echo "+++ Run synapse_port_db a second time"
-coverage run scripts/synapse_port_db --sqlite-database .ci/test_db.db --postgres-config .ci/postgres-config.yaml
+synapse_port_db --sqlite-database .ci/test_db.db --postgres-config .ci/postgres-config.yaml
 
 #####
 
@@ -46,7 +48,7 @@ echo "--- Prepare empty SQLite database"
 # we do this by deleting the sqlite db, and then doing the same again.
 rm .ci/test_db.db
 
-scripts/update_synapse_database --database-config .ci/sqlite-config.yaml --run-background-updates
+update_synapse_database --database-config .ci/sqlite-config.yaml --run-background-updates
 
 # re-create the PostgreSQL database.
 .ci/scripts/postgres_exec.py \
@@ -54,4 +56,4 @@ scripts/update_synapse_database --database-config .ci/sqlite-config.yaml --run-b
   "CREATE DATABASE synapse"
 
 echo "+++ Run synapse_port_db against empty database"
-coverage run scripts/synapse_port_db --sqlite-database .ci/test_db.db --postgres-config .ci/postgres-config.yaml
+synapse_port_db --sqlite-database .ci/test_db.db --postgres-config .ci/postgres-config.yaml
diff --git a/.dockerignore b/.dockerignore
index f6c638b0a221..434231fce9fc 100644
--- a/.dockerignore
+++ b/.dockerignore
@@ -3,11 +3,9 @@
 
 # things to include
 !docker
-!scripts
 !synapse
 !MANIFEST.in
 !README.rst
 !setup.py
-!synctl
 
 **/__pycache__
diff --git a/.github/workflows/release-artifacts.yml b/.github/workflows/release-artifacts.yml
index eee3633d5043..ed4fc6179db3 100644
--- a/.github/workflows/release-artifacts.yml
+++ b/.github/workflows/release-artifacts.yml
@@ -31,7 +31,7 @@ jobs:
           # if we're running from a tag, get the full list of distros; otherwise just use debian:sid
           dists='["debian:sid"]'
           if [[ $GITHUB_REF == refs/tags/* ]]; then
-              dists=$(scripts-dev/build_debian_packages --show-dists-json)
+              dists=$(scripts-dev/build_debian_packages.py --show-dists-json)
           fi
           echo "::set-output name=distros::$dists"
     # map the step outputs to job outputs
@@ -74,7 +74,7 @@ jobs:
         # see https://github.com/docker/build-push-action/issues/252
         # for the cache magic here
         run: |
-          ./src/scripts-dev/build_debian_packages \
+          ./src/scripts-dev/build_debian_packages.py \
             --docker-build-arg=--cache-from=type=local,src=/tmp/.buildx-cache \
             --docker-build-arg=--cache-to=type=local,mode=max,dest=/tmp/.buildx-cache-new \
             --docker-build-arg=--progress=plain \
@@ -112,7 +112,8 @@ jobs:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         with:
           files: |
-            python-dist/*
+            Sdist/*
+            Wheel/*
             debs.tar.xz
           # if it's not already published, keep the release as a draft.
           draft: true
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index e9e427732239..613a773775a2 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -16,7 +16,8 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v2
       - run: pip install -e .
-      - run: scripts-dev/generate_sample_config --check
+      - run: scripts-dev/generate_sample_config.sh --check
+      - run: scripts-dev/config-lint.sh
 
   lint:
     runs-on: ubuntu-latest
@@ -51,7 +52,7 @@ jobs:
           fetch-depth: 0
       - uses: actions/setup-python@v2
       - run: "pip install 'towncrier>=18.6.0rc1'"
-      - run: scripts-dev/check-newsfragment
+      - run: scripts-dev/check-newsfragment.sh
         env:
           PULL_REQUEST_NUMBER: ${{ github.event.number }}
 
@@ -376,7 +377,7 @@ jobs:
       # Run Complement
       - run: |
           set -o pipefail
-          go test -v -json -p 1 -tags synapse_blacklist,msc2403 ./tests/... 2>&1 | gotestfmt
+          go test -v -json -p 1 -tags synapse_blacklist,msc2403,msc2716,msc3030 ./tests/... 2>&1 | gotestfmt
         shell: bash
         name: Run Complement Tests
         env:
@@ -387,34 +388,22 @@ jobs:
   tests-done:
     if: ${{ always() }}
     needs:
+      - check-sampleconfig
       - lint
       - lint-crlf
       - lint-newsfile
       - trial
       - trial-olddeps
       - sytest
+      - export-data
       - portdb
       - complement
     runs-on: ubuntu-latest
     steps:
-      - name: Set build result
-        env:
-          NEEDS_CONTEXT: ${{ toJSON(needs) }}
-        # the `jq` incantation dumps out a series of "<job> <result>" lines.
-        # we set it to an intermediate variable to avoid a pipe, which makes it
-        # hard to set $rc.
-        run: |
-          rc=0
-          results=$(jq -r 'to_entries[] | [.key,.value.result] | join(" ")' <<< $NEEDS_CONTEXT)
-          while read job result ; do
-              # The newsfile lint may be skipped on non PR builds
-              if [ $result == "skipped" ] && [ $job == "lint-newsfile" ]; then
-                continue
-              fi
-
-              if [ "$result" != "success" ]; then
-                  echo "::set-failed ::Job $job returned $result"
-                  rc=1
-              fi
-          done <<< $results
-          exit $rc
+      - uses: matrix-org/done-action@v2
+        with:
+          needs: ${{ toJSON(needs) }}
+
+          # The newsfile lint may be skipped on non PR builds
+          skippable:
+            lint-newsfile
diff --git a/CHANGES.md b/CHANGES.md
index ef671e73f178..6618378c0608 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,3 +1,100 @@
+Synapse 1.55.0 (2022-03-22)
+===========================
+
+This release removes a workaround introduced in Synapse 1.50.0 for Mjolnir compatibility. **This breaks compatibility with Mjolnir 1.3.1 and earlier. ([\#11700](https://github.com/matrix-org/synapse/issues/11700))**; Mjolnir users should upgrade Mjolnir before upgrading Synapse to this version.
+
+This release also moves the location of the `synctl` script; see the [upgrade notes](https://github.com/matrix-org/synapse/blob/develop/docs/upgrade.md#synctl-script-has-been-moved) for more details.
+
+
+Internal Changes
+----------------
+
+- Tweak copy for default Single Sign-On account details template to better adhere to mobile app store guidelines. ([\#12265](https://github.com/matrix-org/synapse/issues/12265), [\#12260](https://github.com/matrix-org/synapse/issues/12260))
+
+
+Synapse 1.55.0rc1 (2022-03-15)
+==============================
+
+Features
+--------
+
+- Add third-party rules callbacks `check_can_shutdown_room` and `check_can_deactivate_user`. ([\#12028](https://github.com/matrix-org/synapse/issues/12028))
+- Improve performance of logging in for large accounts. ([\#12132](https://github.com/matrix-org/synapse/issues/12132))
+- Add experimental env var `SYNAPSE_ASYNC_IO_REACTOR` that causes Synapse to use the asyncio reactor for Twisted. ([\#12135](https://github.com/matrix-org/synapse/issues/12135))
+- Support the stable identifiers from [MSC3440](https://github.com/matrix-org/matrix-doc/pull/3440): threads. ([\#12151](https://github.com/matrix-org/synapse/issues/12151))
+- Add a new Jinja2 template filter to extract the local part of an email address. ([\#12212](https://github.com/matrix-org/synapse/issues/12212))
+
+
+Bugfixes
+--------
+
+- Use the proper serialization format for bundled thread aggregations. The bug has existed since Synapse v1.48.0. ([\#12090](https://github.com/matrix-org/synapse/issues/12090))
+- Fix a long-standing bug when redacting events with relations. ([\#12113](https://github.com/matrix-org/synapse/issues/12113), [\#12121](https://github.com/matrix-org/synapse/issues/12121), [\#12130](https://github.com/matrix-org/synapse/issues/12130), [\#12189](https://github.com/matrix-org/synapse/issues/12189))
+- Fix a bug introduced in Synapse 1.7.2 whereby background updates are never run with the default background batch size. ([\#12157](https://github.com/matrix-org/synapse/issues/12157))
+- Fix a bug where non-standard information was returned from the `/hierarchy` API. Introduced in Synapse v1.41.0. ([\#12175](https://github.com/matrix-org/synapse/issues/12175))
+- Fix a bug introduced in Synapse 1.54.0 that broke background updates on sqlite homeservers while search was disabled. ([\#12215](https://github.com/matrix-org/synapse/issues/12215))
+- Fix a long-standing bug when a `filter` argument with `event_fields` which did not include the `unsigned` field could result in a 500 error on `/sync`. ([\#12234](https://github.com/matrix-org/synapse/issues/12234))
+
+
+Improved Documentation
+----------------------
+
+- Fix complexity checking config example in [Resource Constrained Devices](https://matrix-org.github.io/synapse/v1.54/other/running_synapse_on_single_board_computers.html) docs page. ([\#11998](https://github.com/matrix-org/synapse/issues/11998))
+- Improve documentation for demo scripts. ([\#12143](https://github.com/matrix-org/synapse/issues/12143))
+- Updates to the Room DAG concepts development document. ([\#12179](https://github.com/matrix-org/synapse/issues/12179))
+- Document that the `typing`, `to_device`, `account_data`, `receipts`, and `presence` stream writer can only be used on a single worker. ([\#12196](https://github.com/matrix-org/synapse/issues/12196))
+- Document that contributors can sign off privately by email. ([\#12204](https://github.com/matrix-org/synapse/issues/12204))
+
+
+Deprecations and Removals
+-------------------------
+
+- **Remove workaround introduced in Synapse 1.50.0 for Mjolnir compatibility. Breaks compatibility with Mjolnir 1.3.1 and earlier. ([\#11700](https://github.com/matrix-org/synapse/issues/11700))**
+- **`synctl` has been moved into into `synapse._scripts` and is exposed as an entry point; see [upgrade notes](https://github.com/matrix-org/synapse/blob/develop/docs/upgrade.md#synctl-script-has-been-moved). ([\#12140](https://github.com/matrix-org/synapse/issues/12140))
+- Remove backwards compatibilty with pagination tokens from the `/relations` and `/aggregations` endpoints generated from Synapse < v1.52.0. ([\#12138](https://github.com/matrix-org/synapse/issues/12138))
+- The groups/communities feature in Synapse has been deprecated. ([\#12200](https://github.com/matrix-org/synapse/issues/12200))
+
+
+Internal Changes
+----------------
+
+- Simplify the `ApplicationService` class' set of public methods related to interest checking. ([\#11915](https://github.com/matrix-org/synapse/issues/11915))
+- Add config settings for background update parameters. ([\#11980](https://github.com/matrix-org/synapse/issues/11980))
+- Correct type hints for txredis. ([\#12042](https://github.com/matrix-org/synapse/issues/12042))
+- Limit the size of `aggregation_key` on annotations. ([\#12101](https://github.com/matrix-org/synapse/issues/12101))
+- Add type hints to tests files. ([\#12108](https://github.com/matrix-org/synapse/issues/12108), [\#12146](https://github.com/matrix-org/synapse/issues/12146), [\#12207](https://github.com/matrix-org/synapse/issues/12207), [\#12208](https://github.com/matrix-org/synapse/issues/12208))
+- Move scripts to Synapse package and expose as setuptools entry points. ([\#12118](https://github.com/matrix-org/synapse/issues/12118))
+- Add support for cancellation to `ReadWriteLock`. ([\#12120](https://github.com/matrix-org/synapse/issues/12120))
+- Fix data validation to compare to lists, not sequences. ([\#12128](https://github.com/matrix-org/synapse/issues/12128))
+- Fix CI not attaching source distributions and wheels to the GitHub releases. ([\#12131](https://github.com/matrix-org/synapse/issues/12131))
+- Remove unused mocks from `test_typing`. ([\#12136](https://github.com/matrix-org/synapse/issues/12136))
+- Give `scripts-dev` scripts suffixes for neater CI config. ([\#12137](https://github.com/matrix-org/synapse/issues/12137))
+- Move the snapcraft configuration file to `contrib`. ([\#12142](https://github.com/matrix-org/synapse/issues/12142))
+- Enable [MSC3030](https://github.com/matrix-org/matrix-doc/pull/3030) Complement tests in CI. ([\#12144](https://github.com/matrix-org/synapse/issues/12144))
+- Enable [MSC2716](https://github.com/matrix-org/matrix-doc/pull/2716) Complement tests in CI. ([\#12145](https://github.com/matrix-org/synapse/issues/12145))
+- Add test for `ObservableDeferred`'s cancellation behaviour. ([\#12149](https://github.com/matrix-org/synapse/issues/12149))
+- Use `ParamSpec` in type hints for `synapse.logging.context`. ([\#12150](https://github.com/matrix-org/synapse/issues/12150))
+- Prune unused jobs from `tox` config. ([\#12152](https://github.com/matrix-org/synapse/issues/12152))
+- Move CI checks out of tox, to facilitate a move to using poetry. ([\#12153](https://github.com/matrix-org/synapse/issues/12153))
+- Avoid generating state groups for local out-of-band leaves. ([\#12154](https://github.com/matrix-org/synapse/issues/12154))
+- Avoid trying to calculate the state at outlier events. ([\#12155](https://github.com/matrix-org/synapse/issues/12155), [\#12173](https://github.com/matrix-org/synapse/issues/12173), [\#12202](https://github.com/matrix-org/synapse/issues/12202))
+- Fix some type annotations. ([\#12156](https://github.com/matrix-org/synapse/issues/12156))
+- Add type hints for `ObservableDeferred` attributes. ([\#12159](https://github.com/matrix-org/synapse/issues/12159))
+- Use a prebuilt Action for the `tests-done` CI job. ([\#12161](https://github.com/matrix-org/synapse/issues/12161))
+- Reduce number of DB queries made during processing of `/sync`. ([\#12163](https://github.com/matrix-org/synapse/issues/12163))
+- Add `delay_cancellation` utility function, which behaves like `stop_cancellation` but waits until the original `Deferred` resolves before raising a `CancelledError`. ([\#12180](https://github.com/matrix-org/synapse/issues/12180))
+- Retry HTTP replication failures, this should prevent 502's when restarting stateful workers (main, event persisters, stream writers). Contributed by Nick @ Beeper. ([\#12182](https://github.com/matrix-org/synapse/issues/12182))
+- Add cancellation support to `@cached` and `@cachedList` decorators. ([\#12183](https://github.com/matrix-org/synapse/issues/12183))
+- Remove unused variables. ([\#12187](https://github.com/matrix-org/synapse/issues/12187))
+- Add combined test for HTTP pusher and push rule. Contributed by Nick @ Beeper. ([\#12188](https://github.com/matrix-org/synapse/issues/12188))
+- Rename `HomeServer.get_tcp_replication` to `get_replication_command_handler`. ([\#12192](https://github.com/matrix-org/synapse/issues/12192))
+- Remove some dead code. ([\#12197](https://github.com/matrix-org/synapse/issues/12197))
+- Fix a misleading comment in the function `check_event_for_spam`. ([\#12203](https://github.com/matrix-org/synapse/issues/12203))
+- Remove unnecessary `pass` statements. ([\#12206](https://github.com/matrix-org/synapse/issues/12206))
+- Update the SSO username picker template to comply with SIWA guidelines. ([\#12210](https://github.com/matrix-org/synapse/issues/12210))
+- Improve code documentation for the typing stream over replication. ([\#12211](https://github.com/matrix-org/synapse/issues/12211))
+
+
 Synapse 1.54.0 (2022-03-08)
 ===========================
 
diff --git a/MANIFEST.in b/MANIFEST.in
index 76d14eb642b2..d744c090acde 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -1,4 +1,3 @@
-include synctl
 include LICENSE
 include VERSION
 include *.rst
@@ -17,7 +16,6 @@ recursive-include synapse/storage *.txt
 recursive-include synapse/storage *.md
 
 recursive-include docs *
-recursive-include scripts *
 recursive-include scripts-dev *
 recursive-include synapse *.pyi
 recursive-include tests *.py
@@ -53,5 +51,4 @@ prune contrib
 prune debian
 prune demo/etc
 prune docker
-prune snap
 prune stubs
diff --git a/README.rst b/README.rst
index 4281c87d1f80..595fb5ff62a6 100644
--- a/README.rst
+++ b/README.rst
@@ -312,6 +312,9 @@ We recommend using the demo which starts 3 federated instances running on ports
 
 (to stop, you can use `./demo/stop.sh`)
 
+See the [demo documentation](https://matrix-org.github.io/synapse/develop/development/demo.html)
+for more information.
+
 If you just want to start a single instance of the app and run it directly::
 
     # Create the homeserver.yaml config once
diff --git a/snap/snapcraft.yaml b/contrib/snap/snapcraft.yaml
similarity index 97%
rename from snap/snapcraft.yaml
rename to contrib/snap/snapcraft.yaml
index 9a01152c156b..dd4c8478d59d 100644
--- a/snap/snapcraft.yaml
+++ b/contrib/snap/snapcraft.yaml
@@ -20,7 +20,7 @@ apps:
   generate-config:
     command: generate_config
   generate-signing-key:
-    command: generate_signing_key.py
+    command: generate_signing_key
   register-new-matrix-user:
     command: register_new_matrix_user
     plugs: [network]
diff --git a/debian/changelog b/debian/changelog
index 02136a0d606f..7eed6c5b4a1a 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,3 +1,15 @@
+matrix-synapse-py3 (1.55.0) stable; urgency=medium
+
+  * New synapse release 1.55.0.
+
+ -- Synapse Packaging team <packages@matrix.org>  Tue, 22 Mar 2022 13:59:26 +0000
+
+matrix-synapse-py3 (1.55.0~rc1) stable; urgency=medium
+
+  * New synapse release 1.55.0~rc1.
+
+ -- Synapse Packaging team <packages@matrix.org>  Tue, 15 Mar 2022 10:59:31 +0000
+
 matrix-synapse-py3 (1.54.0) stable; urgency=medium
 
   * New synapse release 1.54.0.
diff --git a/demo/.gitignore b/demo/.gitignore
index 4d1271234312..5663aba8e758 100644
--- a/demo/.gitignore
+++ b/demo/.gitignore
@@ -1,7 +1,4 @@
-*.db
-*.log
-*.log.*
-*.pid
-
-/media_store.*
-/etc
+# Ignore all the temporary files from the demo servers.
+8080/
+8081/
+8082/
diff --git a/demo/README b/demo/README
deleted file mode 100644
index a5a95bd19666..000000000000
--- a/demo/README
+++ /dev/null
@@ -1,26 +0,0 @@
-DO NOT USE THESE DEMO SERVERS IN PRODUCTION
-
-Requires you to have done:
-    python setup.py develop
-
-
-The demo start.sh will start three synapse servers on ports 8080, 8081 and 8082, with host names localhost:$port. This can be easily changed to `hostname`:$port in start.sh if required.
-
-To enable the servers to communicate untrusted ssl certs are used. In order to do this the servers do not check the certs
-and are configured in a highly insecure way. Do not use these configuration files in production.
-
-stop.sh will stop the synapse servers and the webclient.
-
-clean.sh will delete the databases and log files.
-
-To start a completely new set of servers, run:
-
-    ./demo/stop.sh; ./demo/clean.sh && ./demo/start.sh
-
-
-Logs and sqlitedb will be stored in demo/808{0,1,2}.{log,db}
-
-
-
-Also note that when joining a public room on a different HS via "#foo:bar.net", then you are (in the current impl) joining a room with room_id "foo". This means that it won't work if your HS already has a room with that name.
-
diff --git a/demo/clean.sh b/demo/clean.sh
index e9b440d90dfd..7f1e1920215a 100755
--- a/demo/clean.sh
+++ b/demo/clean.sh
@@ -4,6 +4,9 @@ set -e
 
 DIR="$( cd "$( dirname "$0" )" && pwd )"
 
+# Ensure that the servers are stopped.
+$DIR/stop.sh
+
 PID_FILE="$DIR/servers.pid"
 
 if [ -f "$PID_FILE" ]; then
diff --git a/demo/start.sh b/demo/start.sh
index 8ffb14e30add..55e69685e3c2 100755
--- a/demo/start.sh
+++ b/demo/start.sh
@@ -6,8 +6,6 @@ CWD=$(pwd)
 
 cd "$DIR/.." || exit
 
-mkdir -p demo/etc
-
 PYTHONPATH=$(readlink -f "$(pwd)")
 export PYTHONPATH
 
@@ -21,22 +19,26 @@ for port in 8080 8081 8082; do
     mkdir -p demo/$port
     pushd demo/$port || exit
 
-    #rm $DIR/etc/$port.config
+    # Generate the configuration for the homeserver at localhost:848x.
     python3 -m synapse.app.homeserver \
         --generate-config \
-        -H "localhost:$https_port" \
-        --config-path "$DIR/etc/$port.config" \
+        --server-name "localhost:$port" \
+        --config-path "$port.config" \
         --report-stats no
 
-    if ! grep -F "Customisation made by demo/start.sh" -q "$DIR/etc/$port.config"; then
-        # Generate tls keys
-        openssl req -x509 -newkey rsa:4096 -keyout "$DIR/etc/localhost:$https_port.tls.key" -out "$DIR/etc/localhost:$https_port.tls.crt" -days 365 -nodes -subj "/O=matrix"
+    if ! grep -F "Customisation made by demo/start.sh" -q "$port.config"; then
+        # Generate TLS keys.
+        openssl req -x509 -newkey rsa:4096 \
+          -keyout "localhost:$port.tls.key" \
+          -out "localhost:$port.tls.crt" \
+          -days 365 -nodes -subj "/O=matrix"
 
-        # Regenerate configuration
+        # Add customisations to the configuration.
         {
-            printf '\n\n# Customisation made by demo/start.sh\n'
+            printf '\n\n# Customisation made by demo/start.sh\n\n'
             echo "public_baseurl: http://localhost:$port/"
             echo 'enable_registration: true'
+            echo ''
 
 			# Warning, this heredoc depends on the interaction of tabs and spaces.
 			# Please don't accidentaly bork me with your fancy settings.
@@ -63,38 +65,34 @@ for port in 8080 8081 8082; do
 
             echo "${listeners}"
 
-            # Disable tls for the servers
-            printf '\n\n# Disable tls on the servers.'
+            # Disable TLS for the servers
+            printf '\n\n# Disable TLS for the servers.'
             echo '# DO NOT USE IN PRODUCTION'
             echo 'use_insecure_ssl_client_just_for_testing_do_not_use: true'
             echo 'federation_verify_certificates: false'
 
-            # Set tls paths
-            echo "tls_certificate_path: \"$DIR/etc/localhost:$https_port.tls.crt\""
-            echo "tls_private_key_path: \"$DIR/etc/localhost:$https_port.tls.key\""
+            # Set paths for the TLS certificates.
+            echo "tls_certificate_path: \"$DIR/$port/localhost:$port.tls.crt\""
+            echo "tls_private_key_path: \"$DIR/$port/localhost:$port.tls.key\""
 
             # Ignore keys from the trusted keys server
             echo '# Ignore keys from the trusted keys server'
             echo 'trusted_key_servers:'
             echo '  - server_name: "matrix.org"'
             echo '    accept_keys_insecurely: true'
-
-			# Reduce the blacklist
-			blacklist=$(cat <<-BLACK
-			# Set the blacklist so that it doesn't include 127.0.0.1, ::1
-			federation_ip_range_blacklist:
-			  - '10.0.0.0/8'
-			  - '172.16.0.0/12'
-			  - '192.168.0.0/16'
-			  - '100.64.0.0/10'
-			  - '169.254.0.0/16'
-			  - 'fe80::/64'
-			  - 'fc00::/7'
-			BLACK
+            echo ''
+
+			# Allow the servers to communicate over localhost.
+			allow_list=$(cat <<-ALLOW_LIST
+			# Allow the servers to communicate over localhost.
+			ip_range_whitelist:
+			  - '127.0.0.1/8'
+			  - '::1/128'
+			ALLOW_LIST
 			)
 
-            echo "${blacklist}"
-        } >> "$DIR/etc/$port.config"
+            echo "${allow_list}"
+        } >> "$port.config"
     fi
 
     # Check script parameters
@@ -141,19 +139,18 @@ for port in 8080 8081 8082; do
 			    burst_count: 1000
 			RC
 			)
-            echo "${ratelimiting}" >> "$DIR/etc/$port.config"
+            echo "${ratelimiting}" >> "$port.config"
         fi
     fi
 
-    if ! grep -F "full_twisted_stacktraces" -q  "$DIR/etc/$port.config"; then
-        echo "full_twisted_stacktraces: true" >> "$DIR/etc/$port.config"
-    fi
-    if ! grep -F "report_stats" -q  "$DIR/etc/$port.config" ; then
-        echo "report_stats: false" >> "$DIR/etc/$port.config"
+    # Always disable reporting of stats if the option is not there.
+    if ! grep -F "report_stats" -q  "$port.config" ; then
+        echo "report_stats: false" >> "$port.config"
     fi
 
+    # Run the homeserver in the background.
     python3 -m synapse.app.homeserver \
-        --config-path "$DIR/etc/$port.config" \
+        --config-path "$port.config" \
         -D \
 
     popd || exit
diff --git a/docker/Dockerfile b/docker/Dockerfile
index 3d9f42c9fe04..0cac1f4e1b0f 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -38,8 +38,7 @@ RUN apt-get update && apt-get install -y \
     && rm -rf /var/lib/apt/lists/*
 
 # Copy just what we need to pip install
-COPY scripts /synapse/scripts/
-COPY MANIFEST.in README.rst setup.py synctl /synapse/
+COPY MANIFEST.in README.rst setup.py /synapse/
 COPY synapse/__init__.py /synapse/synapse/__init__.py
 COPY synapse/python_dependencies.py /synapse/synapse/python_dependencies.py
 
diff --git a/docs/SUMMARY.md b/docs/SUMMARY.md
index ef9cabf55524..21f80efc9998 100644
--- a/docs/SUMMARY.md
+++ b/docs/SUMMARY.md
@@ -82,6 +82,7 @@
   - [Release Cycle](development/releases.md)
   - [Git Usage](development/git.md)
   - [Testing]()
+    - [Demo scripts](development/demo.md)
   - [OpenTracing](opentracing.md)
   - [Database Schemas](development/database_schema.md)
   - [Experimental features](development/experimental_features.md)
diff --git a/docs/code_style.md b/docs/code_style.md
index 4d8e7c973d05..e7c9cd1a5e4f 100644
--- a/docs/code_style.md
+++ b/docs/code_style.md
@@ -172,6 +172,6 @@ frobber:
 ```
 
 Note that the sample configuration is generated from the synapse code
-and is maintained by a script, `scripts-dev/generate_sample_config`.
+and is maintained by a script, `scripts-dev/generate_sample_config.sh`.
 Making sure that the output from this script matches the desired format
 is left as an exercise for the reader!
diff --git a/docs/development/contributing_guide.md b/docs/development/contributing_guide.md
index 8448685952dc..071202e1965f 100644
--- a/docs/development/contributing_guide.md
+++ b/docs/development/contributing_guide.md
@@ -458,6 +458,17 @@ Git allows you to add this signoff automatically when using the `-s`
 flag to `git commit`, which uses the name and email set in your
 `user.name` and `user.email` git configs.
 
+### Private Sign off
+
+If you would like to provide your legal name privately to the Matrix.org
+Foundation (instead of in a public commit or comment), you can do so
+by emailing your legal name and a link to the pull request to
+[dco@matrix.org](mailto:dco@matrix.org?subject=Private%20sign%20off).
+It helps to include "sign off" or similar in the subject line. You will then
+be instructed further.
+
+Once private sign off is complete, doing so for future contributions will not
+be required.
 
 # 10. Turn feedback into better code.
 
diff --git a/docs/development/database_schema.md b/docs/development/database_schema.md
index a767d3af9fd3..d996a7caa2c6 100644
--- a/docs/development/database_schema.md
+++ b/docs/development/database_schema.md
@@ -158,9 +158,9 @@ same as integers.
 There are three separate aspects to this:
 
  * Any new boolean column must be added to the `BOOLEAN_COLUMNS` list in
-   `scripts/synapse_port_db`. This tells the port script to cast the integer
-   value from SQLite to a boolean before writing the value to the postgres
-   database.
+   `synapse/_scripts/synapse_port_db.py`. This tells the port script to cast
+   the integer value from SQLite to a boolean before writing the value to the
+   postgres database.
 
  * Before SQLite 3.23, `TRUE` and `FALSE` were not recognised as constants by
    SQLite, and the `IS [NOT] TRUE`/`IS [NOT] FALSE` operators were not
diff --git a/docs/development/demo.md b/docs/development/demo.md
new file mode 100644
index 000000000000..4277252ceb60
--- /dev/null
+++ b/docs/development/demo.md
@@ -0,0 +1,41 @@
+# Synapse demo setup
+
+**DO NOT USE THESE DEMO SERVERS IN PRODUCTION**
+
+Requires you to have a [Synapse development environment setup](https://matrix-org.github.io/synapse/develop/development/contributing_guide.html#4-install-the-dependencies).
+
+The demo setup allows running three federation Synapse servers, with server
+names `localhost:8080`, `localhost:8081`, and `localhost:8082`.
+
+You can access them via any Matrix client over HTTP at `localhost:8080`,
+`localhost:8081`, and `localhost:8082` or over HTTPS at `localhost:8480`,
+`localhost:8481`, and `localhost:8482`.
+
+To enable the servers to communicate, self-signed SSL certificates are generated
+and the servers are configured in a highly insecure way, including:
+
+* Not checking certificates over federation.
+* Not verifying keys.
+
+The servers are configured to store their data under `demo/8080`, `demo/8081`, and
+`demo/8082`. This includes configuration, logs, SQLite databases, and media.
+
+Note that when joining a public room on a different HS via "#foo:bar.net", then
+you are (in the current impl) joining a room with room_id "foo". This means that
+it won't work if your HS already has a room with that name.
+
+## Using the demo scripts
+
+There's three main scripts with straightforward purposes:
+
+* `start.sh` will start the Synapse servers, generating any missing configuration.
+  * This accepts a single parameter `--no-rate-limit` to "disable" rate limits
+    (they actually still exist, but are very high).
+* `stop.sh` will stop the Synapse servers.
+* `clean.sh` will delete the configuration, databases, log files, etc.
+
+To start a completely new set of servers, run:
+
+```sh
+./demo/stop.sh; ./demo/clean.sh && ./demo/start.sh
+```
diff --git a/docs/development/room-dag-concepts.md b/docs/development/room-dag-concepts.md
index cbc7cf29491c..3eb4d5acc463 100644
--- a/docs/development/room-dag-concepts.md
+++ b/docs/development/room-dag-concepts.md
@@ -30,37 +30,72 @@ rather than skipping any that arrived late; whereas if you're looking at a
 historical section of timeline (i.e. `/messages`), you want to see the best
 representation of the state of the room as others were seeing it at the time.
 
+## Outliers
 
-## Forward extremity
+We mark an event as an `outlier` when we haven't figured out the state for the
+room at that point in the DAG yet. They are "floating" events that we haven't
+yet correlated to the DAG.
 
-Most-recent-in-time events in the DAG which are not referenced by any other events' `prev_events` yet.
+Outliers typically arise when we fetch the auth chain or state for a given
+event. When that happens, we just grab the events in the state/auth chain,
+without calculating the state at those events, or backfilling their
+`prev_events`.
 
-The forward extremities of a room are used as the `prev_events` when the next event is sent.
+So, typically, we won't have the `prev_events` of an `outlier` in the database,
+(though it's entirely possible that we *might* have them for some other
+reason). Other things that make outliers different from regular events:
 
+ * We don't have state for them, so there should be no entry in
+   `event_to_state_groups` for an outlier. (In practice this isn't always
+   the case, though I'm not sure why: see https://github.com/matrix-org/synapse/issues/12201).
 
-## Backward extremity
+ * We don't record entries for them in the `event_edges`,
+   `event_forward_extremeties` or `event_backward_extremities` tables.
 
-The current marker of where we have backfilled up to and will generally be the
-`prev_events` of the oldest-in-time events we have in the DAG. This gives a starting point when
-backfilling history.
+Since outliers are not tied into the DAG, they do not normally form part of the
+timeline sent down to clients via `/sync` or `/messages`; however there is an
+exception:
 
-When we persist a non-outlier event, we clear it as a backward extremity and set
-all of its `prev_events` as the new backward extremities if they aren't already
-persisted in the `events` table.
+### Out-of-band membership events
 
+A special case of outlier events are some membership events for federated rooms
+that we aren't full members of. For example:
 
-## Outliers
+ * invites received over federation, before we join the room
+ * *rejections* for said invites
+ * knock events for rooms that we would like to join but have not yet joined.
 
-We mark an event as an `outlier` when we haven't figured out the state for the
-room at that point in the DAG yet.
+In all the above cases, we don't have the state for the room, which is why they
+are treated as outliers. They are a bit special though, in that they are
+proactively sent to clients via `/sync`.
 
-We won't *necessarily* have the `prev_events` of an `outlier` in the database,
-but it's entirely possible that we *might*.
+## Forward extremity
+
+Most-recent-in-time events in the DAG which are not referenced by any other
+events' `prev_events` yet. (In this definition, outliers, rejected events, and
+soft-failed events don't count.)
+
+The forward extremities of a room (or at least, a subset of them, if there are
+more than ten) are used as the `prev_events` when the next event is sent.
+
+The "current state" of a room (ie: the state which would be used if we
+generated a new event) is, therefore, the resolution of the room states
+at each of the forward extremities.
+
+## Backward extremity
+
+The current marker of where we have backfilled up to and will generally be the
+`prev_events` of the oldest-in-time events we have in the DAG. This gives a starting point when
+backfilling history.
 
-For example, when we fetch the event auth chain or state for a given event, we
-mark all of those claimed auth events as outliers because we haven't done the
-state calculation ourself.
+Note that, unlike forward extremities, we typically don't have any backward
+extremity events themselves in the database - or, if we do, they will be "outliers" (see
+above). Either way, we don't expect to have the room state at a backward extremity.
 
+When we persist a non-outlier event, if it was previously a backward extremity,
+we clear it as a backward extremity and set all of its `prev_events` as the new
+backward extremities if they aren't already persisted as non-outliers. This
+therefore keeps the backward extremities up-to-date.
 
 ## State groups
 
diff --git a/docs/federate.md b/docs/federate.md
index 5107f995be98..df4c87da51e2 100644
--- a/docs/federate.md
+++ b/docs/federate.md
@@ -63,4 +63,5 @@ release of Synapse.
 
 If you want to get up and running quickly with a trio of homeservers in a
 private federation, there is a script in the `demo` directory. This is mainly
-useful just for development purposes. See [demo/README](https://github.com/matrix-org/synapse/tree/develop/demo/).
+useful just for development purposes. See
+[demo scripts](https://matrix-org.github.io/synapse/develop/development/demo.html).
diff --git a/docs/modules/third_party_rules_callbacks.md b/docs/modules/third_party_rules_callbacks.md
index 09ac838107b8..1d3c39967faa 100644
--- a/docs/modules/third_party_rules_callbacks.md
+++ b/docs/modules/third_party_rules_callbacks.md
@@ -148,6 +148,49 @@ deny an incoming event, see [`check_event_for_spam`](spam_checker_callbacks.md#c
 
 If multiple modules implement this callback, Synapse runs them all in order.
 
+### `check_can_shutdown_room`
+
+_First introduced in Synapse v1.55.0_
+
+```python
+async def check_can_shutdown_room(
+    user_id: str, room_id: str,
+) -> bool:
+```
+
+Called when an admin user requests the shutdown of a room. The module must return a
+boolean indicating whether the shutdown can go through. If the callback returns `False`,
+the shutdown will not proceed and the caller will see a `M_FORBIDDEN` error.
+
+If multiple modules implement this callback, they will be considered in order. If a
+callback returns `True`, Synapse falls through to the next one. The value of the first
+callback that does not return `True` will be used. If this happens, Synapse will not call
+any of the subsequent implementations of this callback.
+
+### `check_can_deactivate_user`
+
+_First introduced in Synapse v1.55.0_
+
+```python
+async def check_can_deactivate_user(
+    user_id: str, by_admin: bool,
+) -> bool:
+```
+
+Called when the deactivation of a user is requested. User deactivation can be
+performed by an admin or the user themselves, so developers are encouraged to check the
+requester when implementing this callback. The module must return a
+boolean indicating whether the deactivation can go through. If the callback returns `False`,
+the deactivation will not proceed and the caller will see a `M_FORBIDDEN` error.
+
+The module is passed two parameters, `user_id` which is the ID of the user being deactivated, and `by_admin` which is `True` if the request is made by a serve admin, and `False` otherwise.
+
+If multiple modules implement this callback, they will be considered in order. If a
+callback returns `True`, Synapse falls through to the next one. The value of the first
+callback that does not return `True` will be used. If this happens, Synapse will not call
+any of the subsequent implementations of this callback.
+
+
 ### `on_profile_update`
 
 _First introduced in Synapse v1.54.0_
diff --git a/docs/other/running_synapse_on_single_board_computers.md b/docs/other/running_synapse_on_single_board_computers.md
index ea14afa8b2df..dcf96f0056ba 100644
--- a/docs/other/running_synapse_on_single_board_computers.md
+++ b/docs/other/running_synapse_on_single_board_computers.md
@@ -31,28 +31,29 @@ Anything that requires modifying the device list [#7721](https://github.com/matr
 Put the below in a new file at /etc/matrix-synapse/conf.d/sbc.yaml to override the defaults in homeserver.yaml.
 
 ```
-# Set to false to disable presence tracking on this homeserver.
+# Disable presence tracking, which is currently fairly resource intensive
+# More info: https://github.com/matrix-org/synapse/issues/9478
 use_presence: false
 
-# When this is enabled, the room "complexity" will be checked before a user
-# joins a new remote room. If it is above the complexity limit, the server will
-# disallow joining, or will instantly leave.
+# Set a small complexity limit, preventing users from joining large rooms
+# which may be resource-intensive to remain a part of.
+#
+# Note that this will not prevent users from joining smaller rooms that
+# eventually become complex.
 limit_remote_rooms:
-  # Uncomment to enable room complexity checking.
-  #enabled: true
+  enabled: true
   complexity: 3.0
 
 # Database configuration
 database:
+  # Use postgres for the best performance
   name: psycopg2
   args:
     user: matrix-synapse
-    # Generate a long, secure one with a password manager
+    # Generate a long, secure password using a password manager
     password: hunter2
     database: matrix-synapse
     host: localhost
-    cp_min: 5
-    cp_max: 10
 ```
 
 Currently the complexity is measured by [current_state_events / 500](https://github.com/matrix-org/synapse/blob/v1.20.1/synapse/storage/databases/main/events_worker.py#L986). You can find join times and your most complex rooms like this:
diff --git a/docs/postgres.md b/docs/postgres.md
index 0562021da526..de4e2ba4b756 100644
--- a/docs/postgres.md
+++ b/docs/postgres.md
@@ -153,9 +153,9 @@ database file (typically `homeserver.db`) to another location. Once the
 copy is complete, restart synapse. For instance:
 
 ```sh
-./synctl stop
+synctl stop
 cp homeserver.db homeserver.db.snapshot
-./synctl start
+synctl start
 ```
 
 Copy the old config file into a new config file:
@@ -192,10 +192,10 @@ Once that has completed, change the synapse config to point at the
 PostgreSQL database configuration file `homeserver-postgres.yaml`:
 
 ```sh
-./synctl stop
+synctl stop
 mv homeserver.yaml homeserver-old-sqlite.yaml
 mv homeserver-postgres.yaml homeserver.yaml
-./synctl start
+synctl start
 ```
 
 Synapse should now be running against PostgreSQL.
diff --git a/docs/sample_config.yaml b/docs/sample_config.yaml
index 6f3623c88ab9..36c6c56e58f7 100644
--- a/docs/sample_config.yaml
+++ b/docs/sample_config.yaml
@@ -1947,8 +1947,14 @@ saml2_config:
 #
 #             localpart_template: Jinja2 template for the localpart of the MXID.
 #                 If this is not set, the user will be prompted to choose their
-#                 own username (see 'sso_auth_account_details.html' in the 'sso'
-#                 section of this file).
+#                 own username (see the documentation for the
+#                 'sso_auth_account_details.html' template). This template can
+#                 use the 'localpart_from_email' filter.
+#
+#             confirm_localpart: Whether to prompt the user to validate (or
+#                 change) the generated localpart (see the documentation for the
+#                 'sso_auth_account_details.html' template), instead of
+#                 registering the account right away.
 #
 #             display_name_template: Jinja2 template for the display name to set
 #                 on first login. If unset, no displayname will be set.
@@ -2729,3 +2735,35 @@ redis:
   # Optional password if configured on the Redis instance
   #
   #password: <secret_password>
+
+
+## Background Updates ##
+
+# Background updates are database updates that are run in the background in batches.
+# The duration, minimum batch size, default batch size, whether to sleep between batches and if so, how long to
+# sleep can all be configured. This is helpful to speed up or slow down the updates.
+#
+background_updates:
+    # How long in milliseconds to run a batch of background updates for. Defaults to 100. Uncomment and set
+    # a time to change the default.
+    #
+    #background_update_duration_ms: 500
+
+    # Whether to sleep between updates. Defaults to True. Uncomment to change the default.
+    #
+    #sleep_enabled: false
+
+    # If sleeping between updates, how long in milliseconds to sleep for. Defaults to 1000. Uncomment
+    # and set a duration to change the default.
+    #
+    #sleep_duration_ms: 300
+
+    # Minimum size a batch of background updates can be. Must be greater than 0. Defaults to 1. Uncomment and
+    # set a size to change the default.
+    #
+    #min_batch_size: 10
+
+    # The batch size to use for the first iteration of a new background update. The default is 100.
+    # Uncomment and set a size to change the default.
+    #
+    #default_batch_size: 50
diff --git a/docs/templates.md b/docs/templates.md
index 2b66e9d86294..f87692a4538d 100644
--- a/docs/templates.md
+++ b/docs/templates.md
@@ -36,6 +36,13 @@ Turns a `mxc://` URL for media content into an HTTP(S) one using the homeserver'
 
 Example: `message.sender_avatar_url|mxc_to_http(32,32)`
 
+```python
+localpart_from_email(address: str) -> str
+```
+
+Returns the local part of an email address (e.g. `alice` in `alice@example.com`).
+
+Example: `user.email_address|localpart_from_email`
 
 ## Email templates
 
@@ -176,8 +183,11 @@ Below are the templates Synapse will look for when generating pages related to S
              for the brand of the IdP
     * `user_attributes`: an object containing details about the user that
       we received from the IdP. May have the following attributes:
-        * display_name: the user's display_name
-        * emails: a list of email addresses
+        * `display_name`: the user's display name
+        * `emails`: a list of email addresses
+        * `localpart`: the local part of the Matrix user ID to register,
+          if `localpart_template` is set in the mapping provider configuration (empty
+          string if not)
   The template should render a form which submits the following fields:
     * `username`: the localpart of the user's chosen user id
 * `sso_new_user_consent.html`: HTML page allowing the user to consent to the
diff --git a/docs/turn-howto.md b/docs/turn-howto.md
index eba7ca6124a5..3a2cd04e36a9 100644
--- a/docs/turn-howto.md
+++ b/docs/turn-howto.md
@@ -238,8 +238,9 @@ After updating the homeserver configuration, you must restart synapse:
 
   * If you use synctl:
     ```sh
-    cd /where/you/run/synapse
-    ./synctl restart
+    # Depending on how Synapse is installed, synctl may already be on
+    # your PATH. If not, you may need to activate a virtual environment.
+    synctl restart
     ```
   * If you use systemd:
     ```sh
diff --git a/docs/upgrade.md b/docs/upgrade.md
index f9be3ac6bc15..f9ac605e7b29 100644
--- a/docs/upgrade.md
+++ b/docs/upgrade.md
@@ -47,7 +47,7 @@ this document.
     3.  Restart Synapse:
 
         ```bash
-        ./synctl restart
+        synctl restart
         ```
 
 To check whether your update was successful, you can check the running
@@ -85,6 +85,49 @@ process, for example:
     dpkg -i matrix-synapse-py3_1.3.0+stretch1_amd64.deb
     ```
 
+# Upgrading to v1.56.0
+
+## Groups/communities feature has been deprecated
+
+The non-standard groups/communities feature in Synapse has been deprecated and will
+be disabled by default in Synapse v1.58.0.
+
+You can test disabling it by adding the following to your homeserver configuration:
+
+```yaml
+experimental_features:
+  groups_enabled: false
+```
+
+# Upgrading to v1.55.0
+
+## `synctl` script has been moved
+
+The `synctl` script
+[has been made](https://github.com/matrix-org/synapse/pull/12140) an
+[entry point](https://packaging.python.org/en/latest/specifications/entry-points/)
+and no longer exists at the root of Synapse's source tree. If you wish to use
+`synctl` to manage your homeserver, you should invoke `synctl` directly, e.g. 
+`synctl start` instead of `./synctl start` or `/path/to/synctl start`. 
+
+You will need to ensure `synctl` is on your `PATH`.
+  - This is automatically the case when using
+    [Debian packages](https://packages.matrix.org/debian/) or
+    [docker images](https://hub.docker.com/r/matrixdotorg/synapse)
+    provided by Matrix.org.
+  - When installing from a wheel, sdist, or PyPI, a `synctl` executable is added 
+    to your Python installation's `bin`. This should be on your `PATH`
+    automatically, though you might need to activate a virtual environment
+    depending on how you installed Synapse.
+
+
+## Compatibility dropped for Mjolnir 1.3.1 and earlier
+
+Synapse v1.55.0 drops support for Mjolnir 1.3.1 and earlier.
+If you use the Mjolnir module to moderate your homeserver,
+please upgrade Mjolnir to version 1.3.2 or later before upgrading Synapse.
+
+
 # Upgrading to v1.54.0
 
 ## Legacy structured logging configuration removal
diff --git a/docs/usage/administration/admin_api/README.md b/docs/usage/administration/admin_api/README.md
index 2fca96f8be4e..3cbedc5dfa30 100644
--- a/docs/usage/administration/admin_api/README.md
+++ b/docs/usage/administration/admin_api/README.md
@@ -12,7 +12,7 @@ UPDATE users SET admin = 1 WHERE name = '@foo:bar.com';
 ```
 
 A new server admin user can also be created using the `register_new_matrix_user`
-command. This is a script that is located in the `scripts/` directory, or possibly
+command. This is a script that is distributed as part of synapse. It is possibly
 already on your `$PATH` depending on how Synapse was installed.
 
 Finding your user's `access_token` is client-dependent, but will usually be shown in the client's settings.
diff --git a/docs/workers.md b/docs/workers.md
index b0f8599ef062..8751134e654d 100644
--- a/docs/workers.md
+++ b/docs/workers.md
@@ -351,8 +351,11 @@ is only supported with Redis-based replication.)
 
 To enable this, the worker must have a HTTP replication listener configured,
 have a `worker_name` and be listed in the `instance_map` config. The same worker
-can handle multiple streams. For example, to move event persistence off to a
-dedicated worker, the shared configuration would include:
+can handle multiple streams, but unless otherwise documented, each stream can only
+have a single writer.
+
+For example, to move event persistence off to a dedicated worker, the shared
+configuration would include:
 
 ```yaml
 instance_map:
@@ -370,8 +373,8 @@ streams and the endpoints associated with them:
 
 ##### The `events` stream
 
-The `events` stream also experimentally supports having multiple writers, where
-work is sharded between them by room ID. Note that you *must* restart all worker
+The `events` stream experimentally supports having multiple writers, where work
+is sharded between them by room ID. Note that you *must* restart all worker
 instances when adding or removing event persisters. An example `stream_writers`
 configuration with multiple writers:
 
@@ -384,38 +387,38 @@ stream_writers:
 
 ##### The `typing` stream
 
-The following endpoints should be routed directly to the workers configured as
-stream writers for the `typing` stream:
+The following endpoints should be routed directly to the worker configured as
+the stream writer for the `typing` stream:
 
     ^/_matrix/client/(api/v1|r0|v3|unstable)/rooms/.*/typing
 
 ##### The `to_device` stream
 
-The following endpoints should be routed directly to the workers configured as
-stream writers for the `to_device` stream:
+The following endpoints should be routed directly to the worker configured as
+the stream writer for the `to_device` stream:
 
     ^/_matrix/client/(api/v1|r0|v3|unstable)/sendToDevice/
 
 ##### The `account_data` stream
 
-The following endpoints should be routed directly to the workers configured as
-stream writers for the `account_data` stream:
+The following endpoints should be routed directly to the worker configured as
+the stream writer for the `account_data` stream:
 
     ^/_matrix/client/(api/v1|r0|v3|unstable)/.*/tags
     ^/_matrix/client/(api/v1|r0|v3|unstable)/.*/account_data
 
 ##### The `receipts` stream
 
-The following endpoints should be routed directly to the workers configured as
-stream writers for the `receipts` stream:
+The following endpoints should be routed directly to the worker configured as
+the stream writer for the `receipts` stream:
 
     ^/_matrix/client/(api/v1|r0|v3|unstable)/rooms/.*/receipt
     ^/_matrix/client/(api/v1|r0|v3|unstable)/rooms/.*/read_markers
 
 ##### The `presence` stream
 
-The following endpoints should be routed directly to the workers configured as
-stream writers for the `presence` stream:
+The following endpoints should be routed directly to the worker configured as
+the stream writer for the `presence` stream:
 
     ^/_matrix/client/(api/v1|r0|v3|unstable)/presence/
 
diff --git a/mypy.ini b/mypy.ini
index 38ff78760931..f9c39fcaaee3 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -11,7 +11,7 @@ local_partial_types = True
 no_implicit_optional = True
 
 files =
-  scripts-dev/sign_json,
+  scripts-dev/,
   setup.py,
   synapse/,
   tests/
@@ -23,6 +23,20 @@ files =
 # https://docs.python.org/3/library/re.html#re.X
 exclude = (?x)
   ^(
+   |scripts-dev/build_debian_packages.py
+   |scripts-dev/check_signature.py
+   |scripts-dev/definitions.py
+   |scripts-dev/federation_client.py
+   |scripts-dev/hash_history.py
+   |scripts-dev/list_url_patterns.py
+   |scripts-dev/release.py
+   |scripts-dev/tail-synapse.py
+
+   |synapse/_scripts/export_signing_key.py
+   |synapse/_scripts/move_remote_media_to_new_store.py
+   |synapse/_scripts/synapse_port_db.py
+   |synapse/_scripts/update_synapse_database.py
+
    |synapse/storage/databases/__init__.py
    |synapse/storage/databases/main/__init__.py
    |synapse/storage/databases/main/cache.py
@@ -74,17 +88,8 @@ exclude = (?x)
    |tests/push/test_http.py
    |tests/push/test_presentable_names.py
    |tests/push/test_push_rule_evaluator.py
-   |tests/rest/client/test_account.py
-   |tests/rest/client/test_filter.py
-   |tests/rest/client/test_report_event.py
-   |tests/rest/client/test_rooms.py
-   |tests/rest/client/test_third_party_rules.py
    |tests/rest/client/test_transactions.py
-   |tests/rest/client/test_typing.py
-   |tests/rest/key/v2/test_remote_key_resource.py
-   |tests/rest/media/v1/test_base.py
    |tests/rest/media/v1/test_media_storage.py
-   |tests/rest/media/v1/test_url_preview.py
    |tests/scripts/test_new_matrix_user.py
    |tests/server.py
    |tests/server_notices/test_resource_limits_server_notices.py
@@ -246,10 +251,7 @@ disallow_untyped_defs = True
 [mypy-tests.storage.test_user_directory]
 disallow_untyped_defs = True
 
-[mypy-tests.rest.admin.*]
-disallow_untyped_defs = True
-
-[mypy-tests.rest.client.*]
+[mypy-tests.rest.*]
 disallow_untyped_defs = True
 
 [mypy-tests.federation.transport.test_client]
@@ -350,3 +352,6 @@ ignore_missing_imports = True
 
 [mypy-zope]
 ignore_missing_imports = True
+
+[mypy-incremental.*]
+ignore_missing_imports = True
diff --git a/scripts-dev/build_debian_packages b/scripts-dev/build_debian_packages.py
similarity index 100%
rename from scripts-dev/build_debian_packages
rename to scripts-dev/build_debian_packages.py
diff --git a/scripts-dev/check-newsfragment b/scripts-dev/check-newsfragment.sh
similarity index 100%
rename from scripts-dev/check-newsfragment
rename to scripts-dev/check-newsfragment.sh
diff --git a/scripts-dev/complement.sh b/scripts-dev/complement.sh
index 0aecb3daf158..0a79a4063f5a 100755
--- a/scripts-dev/complement.sh
+++ b/scripts-dev/complement.sh
@@ -71,4 +71,4 @@ fi
 
 # Run the tests!
 echo "Images built; running complement"
-go test -v -tags synapse_blacklist,msc2403 -count=1 $EXTRA_COMPLEMENT_ARGS ./tests/...
+go test -v -tags synapse_blacklist,msc2403,msc2716,msc3030 -count=1 $EXTRA_COMPLEMENT_ARGS ./tests/...
diff --git a/scripts-dev/generate_sample_config b/scripts-dev/generate_sample_config
deleted file mode 100755
index 4cd1d1d5b829..000000000000
--- a/scripts-dev/generate_sample_config
+++ /dev/null
@@ -1,28 +0,0 @@
-#!/usr/bin/env bash
-#
-# Update/check the docs/sample_config.yaml
-
-set -e
-
-cd "$(dirname "$0")/.."
-
-SAMPLE_CONFIG="docs/sample_config.yaml"
-SAMPLE_LOG_CONFIG="docs/sample_log_config.yaml"
-
-check() {
-    diff -u "$SAMPLE_LOG_CONFIG" <(./scripts/generate_log_config) >/dev/null || return 1
-}
-
-if [ "$1" == "--check" ]; then
-    diff -u "$SAMPLE_CONFIG" <(./scripts/generate_config --header-file docs/.sample_config_header.yaml) >/dev/null || {
-        echo -e "\e[1m\e[31m$SAMPLE_CONFIG is not up-to-date. Regenerate it with \`scripts-dev/generate_sample_config\`.\e[0m" >&2
-        exit 1
-    }
-    diff -u "$SAMPLE_LOG_CONFIG" <(./scripts/generate_log_config) >/dev/null || {
-        echo -e "\e[1m\e[31m$SAMPLE_LOG_CONFIG is not up-to-date. Regenerate it with \`scripts-dev/generate_sample_config\`.\e[0m" >&2
-        exit 1
-    }
-else
-    ./scripts/generate_config --header-file docs/.sample_config_header.yaml -o "$SAMPLE_CONFIG"
-    ./scripts/generate_log_config -o "$SAMPLE_LOG_CONFIG"
-fi
diff --git a/scripts-dev/generate_sample_config.sh b/scripts-dev/generate_sample_config.sh
new file mode 100755
index 000000000000..375897eacb67
--- /dev/null
+++ b/scripts-dev/generate_sample_config.sh
@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+#
+# Update/check the docs/sample_config.yaml
+
+set -e
+
+cd "$(dirname "$0")/.."
+
+SAMPLE_CONFIG="docs/sample_config.yaml"
+SAMPLE_LOG_CONFIG="docs/sample_log_config.yaml"
+
+check() {
+    diff -u "$SAMPLE_LOG_CONFIG" <(synapse/_scripts/generate_log_config.py) >/dev/null || return 1
+}
+
+if [ "$1" == "--check" ]; then
+    diff -u "$SAMPLE_CONFIG" <(synapse/_scripts/generate_config.py --header-file docs/.sample_config_header.yaml) >/dev/null || {
+        echo -e "\e[1m\e[31m$SAMPLE_CONFIG is not up-to-date. Regenerate it with \`scripts-dev/generate_sample_config.sh\`.\e[0m" >&2
+        exit 1
+    }
+    diff -u "$SAMPLE_LOG_CONFIG" <(synapse/_scripts/generate_log_config.py) >/dev/null || {
+        echo -e "\e[1m\e[31m$SAMPLE_LOG_CONFIG is not up-to-date. Regenerate it with \`scripts-dev/generate_sample_config.sh\`.\e[0m" >&2
+        exit 1
+    }
+else
+    synapse/_scripts/generate_config.py --header-file docs/.sample_config_header.yaml -o "$SAMPLE_CONFIG"
+    synapse/_scripts/generate_log_config.py -o "$SAMPLE_LOG_CONFIG"
+fi
diff --git a/scripts-dev/lint.sh b/scripts-dev/lint.sh
index b6554a73c115..c063fafa973b 100755
--- a/scripts-dev/lint.sh
+++ b/scripts-dev/lint.sh
@@ -84,17 +84,8 @@ else
       files=(
           "synapse" "docker" "tests"
           # annoyingly, black doesn't find these so we have to list them
-          "scripts/export_signing_key"
-          "scripts/generate_config"
-          "scripts/generate_log_config"
-          "scripts/hash_password"
-          "scripts/register_new_matrix_user"
-          "scripts/synapse_port_db"
-          "scripts/update_synapse_database"
           "scripts-dev"
-          "scripts-dev/build_debian_packages"
-          "scripts-dev/sign_json"
-          "contrib" "synctl" "setup.py" "synmark" "stubs" ".ci"
+          "contrib" "setup.py" "synmark" "stubs" ".ci"
       )
   fi
 fi
diff --git a/scripts-dev/make_full_schema.sh b/scripts-dev/make_full_schema.sh
index c3c90f4ec637..f0e22d4ca25b 100755
--- a/scripts-dev/make_full_schema.sh
+++ b/scripts-dev/make_full_schema.sh
@@ -147,7 +147,7 @@ python -m synapse.app.homeserver --generate-keys -c "$SQLITE_CONFIG"
 
 # Make sure the SQLite3 database is using the latest schema and has no pending background update.
 echo "Running db background jobs..."
-scripts/update_synapse_database --database-config --run-background-updates "$SQLITE_CONFIG"
+synapse/_scripts/update_synapse_database.py --database-config --run-background-updates "$SQLITE_CONFIG"
 
 # Create the PostgreSQL database.
 echo "Creating postgres database..."
@@ -156,10 +156,10 @@ createdb --lc-collate=C --lc-ctype=C --template=template0 "$POSTGRES_DB_NAME"
 echo "Copying data from SQLite3 to Postgres with synapse_port_db..."
 if [ -z "$COVERAGE" ]; then
   # No coverage needed
-  scripts/synapse_port_db --sqlite-database "$SQLITE_DB" --postgres-config "$POSTGRES_CONFIG"
+  synapse/_scripts/synapse_port_db.py --sqlite-database "$SQLITE_DB" --postgres-config "$POSTGRES_CONFIG"
 else
   # Coverage desired
-  coverage run scripts/synapse_port_db --sqlite-database "$SQLITE_DB" --postgres-config "$POSTGRES_CONFIG"
+  coverage run synapse/_scripts/synapse_port_db.py --sqlite-database "$SQLITE_DB" --postgres-config "$POSTGRES_CONFIG"
 fi
 
 # Delete schema_version, applied_schema_deltas and applied_module_schemas tables
diff --git a/scripts-dev/sign_json b/scripts-dev/sign_json.py
similarity index 100%
rename from scripts-dev/sign_json
rename to scripts-dev/sign_json.py
diff --git a/scripts/register_new_matrix_user b/scripts/register_new_matrix_user
deleted file mode 100755
index 00104b9d62cb..000000000000
--- a/scripts/register_new_matrix_user
+++ /dev/null
@@ -1,19 +0,0 @@
-#!/usr/bin/env python
-# Copyright 2015, 2016 OpenMarket Ltd
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-from synapse._scripts.register_new_matrix_user import main
-
-if __name__ == "__main__":
-    main()
diff --git a/scripts/synapse_review_recent_signups b/scripts/synapse_review_recent_signups
deleted file mode 100755
index a36d46e14cde..000000000000
--- a/scripts/synapse_review_recent_signups
+++ /dev/null
@@ -1,19 +0,0 @@
-#!/usr/bin/env python
-# Copyright 2021 The Matrix.org Foundation C.I.C.
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-from synapse._scripts.review_recent_signups import main
-
-if __name__ == "__main__":
-    main()
diff --git a/scripts/sync_room_to_group.pl b/scripts/sync_room_to_group.pl
deleted file mode 100755
index f0c2dfadfa11..000000000000
--- a/scripts/sync_room_to_group.pl
+++ /dev/null
@@ -1,45 +0,0 @@
-#!/usr/bin/env perl
-
-use strict;
-use warnings;
-
-use JSON::XS;
-use LWP::UserAgent;
-use URI::Escape;
-
-if (@ARGV < 4) {
-    die "usage: $0 <homeserver url> <access_token> <room_id|room_alias> <group_id>\n";
-}
-
-my ($hs, $access_token, $room_id, $group_id) = @ARGV;
-my $ua = LWP::UserAgent->new();
-$ua->timeout(10);
-
-if ($room_id =~ /^#/) {
-    $room_id = uri_escape($room_id);
-    $room_id = decode_json($ua->get("${hs}/_matrix/client/r0/directory/room/${room_id}?access_token=${access_token}")->decoded_content)->{room_id};
-}
-
-my $room_users  = [ keys %{decode_json($ua->get("${hs}/_matrix/client/r0/rooms/${room_id}/joined_members?access_token=${access_token}")->decoded_content)->{joined}} ];
-my $group_users = [
-    (map { $_->{user_id} } @{decode_json($ua->get("${hs}/_matrix/client/unstable/groups/${group_id}/users?access_token=${access_token}" )->decoded_content)->{chunk}}),
-    (map { $_->{user_id} } @{decode_json($ua->get("${hs}/_matrix/client/unstable/groups/${group_id}/invited_users?access_token=${access_token}" )->decoded_content)->{chunk}}),
-];
-
-die "refusing to sync from empty room" unless (@$room_users);
-die "refusing to sync to empty group" unless (@$group_users);
-
-my $diff = {};
-foreach my $user (@$room_users) { $diff->{$user}++ }
-foreach my $user (@$group_users) { $diff->{$user}-- }
-
-foreach my $user (keys %$diff) {
-    if ($diff->{$user} == 1) {
-        warn "inviting $user";
-        print STDERR $ua->put("${hs}/_matrix/client/unstable/groups/${group_id}/admin/users/invite/${user}?access_token=${access_token}", Content=>'{}')->status_line."\n";
-    }
-    elsif ($diff->{$user} == -1) {
-        warn "removing $user";
-        print STDERR $ua->put("${hs}/_matrix/client/unstable/groups/${group_id}/admin/users/remove/${user}?access_token=${access_token}", Content=>'{}')->status_line."\n";
-    }
-}
diff --git a/setup.py b/setup.py
index 26f4650348d5..439ed75d7282 100755
--- a/setup.py
+++ b/setup.py
@@ -15,7 +15,6 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-import glob
 import os
 from typing import Any, Dict
 
@@ -153,8 +152,20 @@ def exec_file(path_segments):
     python_requires="~=3.7",
     entry_points={
         "console_scripts": [
+            # Application
             "synapse_homeserver = synapse.app.homeserver:main",
             "synapse_worker = synapse.app.generic_worker:main",
+            "synctl = synapse._scripts.synctl:main",
+            # Scripts
+            "export_signing_key = synapse._scripts.export_signing_key:main",
+            "generate_config = synapse._scripts.generate_config:main",
+            "generate_log_config = synapse._scripts.generate_log_config:main",
+            "generate_signing_key = synapse._scripts.generate_signing_key:main",
+            "hash_password = synapse._scripts.hash_password:main",
+            "register_new_matrix_user = synapse._scripts.register_new_matrix_user:main",
+            "synapse_port_db = synapse._scripts.synapse_port_db:main",
+            "synapse_review_recent_signups = synapse._scripts.review_recent_signups:main",
+            "update_synapse_database = synapse._scripts.update_synapse_database:main",
         ]
     },
     classifiers=[
@@ -167,6 +178,5 @@ def exec_file(path_segments):
         "Programming Language :: Python :: 3.9",
         "Programming Language :: Python :: 3.10",
     ],
-    scripts=["synctl"] + glob.glob("scripts/*"),
     cmdclass={"test": TestCommand},
 )
diff --git a/stubs/txredisapi.pyi b/stubs/txredisapi.pyi
index 429234d7ae7f..2d8ca018fbfc 100644
--- a/stubs/txredisapi.pyi
+++ b/stubs/txredisapi.pyi
@@ -20,7 +20,7 @@ from twisted.internet import protocol
 from twisted.internet.defer import Deferred
 
 class RedisProtocol(protocol.Protocol):
-    def publish(self, channel: str, message: bytes): ...
+    def publish(self, channel: str, message: bytes) -> "Deferred[None]": ...
     def ping(self) -> "Deferred[None]": ...
     def set(
         self,
@@ -52,11 +52,14 @@ def lazyConnection(
     convertNumbers: bool = ...,
 ) -> RedisProtocol: ...
 
-class ConnectionHandler: ...
+# ConnectionHandler doesn't actually inherit from RedisProtocol, but it proxies
+# most methods to it via ConnectionHandler.__getattr__.
+class ConnectionHandler(RedisProtocol):
+    def disconnect(self) -> "Deferred[None]": ...
 
 class RedisFactory(protocol.ReconnectingClientFactory):
     continueTrying: bool
-    handler: RedisProtocol
+    handler: ConnectionHandler
     pool: List[RedisProtocol]
     replyTimeout: Optional[int]
     def __init__(
diff --git a/synapse/__init__.py b/synapse/__init__.py
index c6727024f026..f0f224d0bb4e 100644
--- a/synapse/__init__.py
+++ b/synapse/__init__.py
@@ -25,6 +25,27 @@
     print("Synapse requires Python 3.7 or above.")
     sys.exit(1)
 
+# Allow using the asyncio reactor via env var.
+if bool(os.environ.get("SYNAPSE_ASYNC_IO_REACTOR", False)):
+    try:
+        from incremental import Version
+
+        import twisted
+
+        # We need a bugfix that is included in Twisted 21.2.0:
+        # https://twistedmatrix.com/trac/ticket/9787
+        if twisted.version < Version("Twisted", 21, 2, 0):
+            print("Using asyncio reactor requires Twisted>=21.2.0")
+            sys.exit(1)
+
+        import asyncio
+
+        from twisted.internet import asyncioreactor
+
+        asyncioreactor.install(asyncio.get_event_loop())
+    except ImportError:
+        pass
+
 # Twisted and canonicaljson will fail to import when this file is executed to
 # get the __version__ during a fresh install. That's OK and subsequent calls to
 # actually start Synapse will import these libraries fine.
@@ -47,7 +68,7 @@
 except ImportError:
     pass
 
-__version__ = "1.54.0"
+__version__ = "1.55.0"
 
 if bool(os.environ.get("SYNAPSE_TEST_PATCH_LOG_CONTEXTS", False)):
     # We import here so that we don't have to install a bunch of deps when
diff --git a/scripts/export_signing_key b/synapse/_scripts/export_signing_key.py
similarity index 99%
rename from scripts/export_signing_key
rename to synapse/_scripts/export_signing_key.py
index bf0139bd64b8..3d254348f165 100755
--- a/scripts/export_signing_key
+++ b/synapse/_scripts/export_signing_key.py
@@ -50,7 +50,7 @@ def format_for_config(public_key: nacl.signing.VerifyKey, expiry_ts: int):
     )
 
 
-if __name__ == "__main__":
+def main():
     parser = argparse.ArgumentParser()
 
     parser.add_argument(
@@ -85,7 +85,6 @@ def format_for_config(public_key: nacl.signing.VerifyKey, expiry_ts: int):
         else format_plain
     )
 
-    keys = []
     for file in args.key_file:
         try:
             res = read_signing_keys(file)
@@ -98,3 +97,7 @@ def format_for_config(public_key: nacl.signing.VerifyKey, expiry_ts: int):
             res = []
         for key in res:
             formatter(get_verify_key(key))
+
+
+if __name__ == "__main__":
+    main()
diff --git a/scripts/generate_config b/synapse/_scripts/generate_config.py
similarity index 98%
rename from scripts/generate_config
rename to synapse/_scripts/generate_config.py
index 931b40c045f3..75fce20b1234 100755
--- a/scripts/generate_config
+++ b/synapse/_scripts/generate_config.py
@@ -6,7 +6,8 @@
 
 from synapse.config.homeserver import HomeServerConfig
 
-if __name__ == "__main__":
+
+def main():
     parser = argparse.ArgumentParser()
     parser.add_argument(
         "--config-dir",
@@ -76,3 +77,7 @@
         shutil.copyfileobj(args.header_file, args.output_file)
 
     args.output_file.write(conf)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/scripts/generate_log_config b/synapse/_scripts/generate_log_config.py
similarity index 98%
rename from scripts/generate_log_config
rename to synapse/_scripts/generate_log_config.py
index e72a0dafb769..82fc7631401a 100755
--- a/scripts/generate_log_config
+++ b/synapse/_scripts/generate_log_config.py
@@ -19,7 +19,8 @@
 
 from synapse.config.logger import DEFAULT_LOG_CONFIG
 
-if __name__ == "__main__":
+
+def main():
     parser = argparse.ArgumentParser()
 
     parser.add_argument(
@@ -42,3 +43,7 @@
     out = args.output_file
     out.write(DEFAULT_LOG_CONFIG.substitute(log_file=args.log_file))
     out.flush()
+
+
+if __name__ == "__main__":
+    main()
diff --git a/scripts/generate_signing_key.py b/synapse/_scripts/generate_signing_key.py
similarity index 97%
rename from scripts/generate_signing_key.py
rename to synapse/_scripts/generate_signing_key.py
index 07df25a8099d..bc26d25bfd36 100755
--- a/scripts/generate_signing_key.py
+++ b/synapse/_scripts/generate_signing_key.py
@@ -19,7 +19,8 @@
 
 from synapse.util.stringutils import random_string
 
-if __name__ == "__main__":
+
+def main():
     parser = argparse.ArgumentParser()
 
     parser.add_argument(
@@ -34,3 +35,7 @@
     key_id = "a_" + random_string(4)
     key = (generate_signing_key(key_id),)
     write_signing_keys(args.output_file, key)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/scripts/hash_password b/synapse/_scripts/hash_password.py
similarity index 96%
rename from scripts/hash_password
rename to synapse/_scripts/hash_password.py
index 1d6fb0d70022..708640c7de8d 100755
--- a/scripts/hash_password
+++ b/synapse/_scripts/hash_password.py
@@ -8,9 +8,6 @@
 import bcrypt
 import yaml
 
-bcrypt_rounds = 12
-password_pepper = ""
-
 
 def prompt_for_pass():
     password = getpass.getpass("Password: ")
@@ -26,7 +23,10 @@ def prompt_for_pass():
     return password
 
 
-if __name__ == "__main__":
+def main():
+    bcrypt_rounds = 12
+    password_pepper = ""
+
     parser = argparse.ArgumentParser(
         description=(
             "Calculate the hash of a new password, so that passwords can be reset"
@@ -77,3 +77,7 @@ def prompt_for_pass():
     ).decode("ascii")
 
     print(hashed)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/scripts/move_remote_media_to_new_store.py b/synapse/_scripts/move_remote_media_to_new_store.py
similarity index 97%
rename from scripts/move_remote_media_to_new_store.py
rename to synapse/_scripts/move_remote_media_to_new_store.py
index 875aa4781f49..9667d95dfe44 100755
--- a/scripts/move_remote_media_to_new_store.py
+++ b/synapse/_scripts/move_remote_media_to_new_store.py
@@ -28,7 +28,7 @@
 
 To use, pipe the above into::
 
-    PYTHON_PATH=. ./scripts/move_remote_media_to_new_store.py <source repo> <dest repo>
+    PYTHON_PATH=. synapse/_scripts/move_remote_media_to_new_store.py <source repo> <dest repo>
 """
 
 import argparse
diff --git a/scripts/synapse_port_db b/synapse/_scripts/synapse_port_db.py
similarity index 99%
rename from scripts/synapse_port_db
rename to synapse/_scripts/synapse_port_db.py
index db354b3c8c5c..c38666da18e6 100755
--- a/scripts/synapse_port_db
+++ b/synapse/_scripts/synapse_port_db.py
@@ -1146,7 +1146,7 @@ def set_state(self, state):
 ##############################################
 
 
-if __name__ == "__main__":
+def main():
     parser = argparse.ArgumentParser(
         description="A script to port an existing synapse SQLite database to"
         " a new PostgreSQL database."
@@ -1251,3 +1251,7 @@ def run():
         sys.stderr.write(end_error)
 
         sys.exit(5)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/synctl b/synapse/_scripts/synctl.py
similarity index 100%
rename from synctl
rename to synapse/_scripts/synctl.py
diff --git a/scripts/update_synapse_database b/synapse/_scripts/update_synapse_database.py
similarity index 100%
rename from scripts/update_synapse_database
rename to synapse/_scripts/update_synapse_database.py
diff --git a/synapse/api/constants.py b/synapse/api/constants.py
index 36ace7c6134f..b0c08a074d83 100644
--- a/synapse/api/constants.py
+++ b/synapse/api/constants.py
@@ -178,7 +178,9 @@ class RelationTypes:
     ANNOTATION: Final = "m.annotation"
     REPLACE: Final = "m.replace"
     REFERENCE: Final = "m.reference"
-    THREAD: Final = "io.element.thread"
+    THREAD: Final = "m.thread"
+    # TODO Remove this in Synapse >= v1.57.0.
+    UNSTABLE_THREAD: Final = "io.element.thread"
 
 
 class LimitBlockingTypes:
diff --git a/synapse/api/filtering.py b/synapse/api/filtering.py
index cb532d723828..27e97d6f372d 100644
--- a/synapse/api/filtering.py
+++ b/synapse/api/filtering.py
@@ -88,7 +88,9 @@
         "org.matrix.labels": {"type": "array", "items": {"type": "string"}},
         "org.matrix.not_labels": {"type": "array", "items": {"type": "string"}},
         # MSC3440, filtering by event relations.
+        "related_by_senders": {"type": "array", "items": {"type": "string"}},
         "io.element.relation_senders": {"type": "array", "items": {"type": "string"}},
+        "related_by_rel_types": {"type": "array", "items": {"type": "string"}},
         "io.element.relation_types": {"type": "array", "items": {"type": "string"}},
     },
 }
@@ -318,19 +320,18 @@ def __init__(self, hs: "HomeServer", filter_json: JsonDict):
         self.labels = filter_json.get("org.matrix.labels", None)
         self.not_labels = filter_json.get("org.matrix.not_labels", [])
 
-        # Ideally these would be rejected at the endpoint if they were provided
-        # and not supported, but that would involve modifying the JSON schema
-        # based on the homeserver configuration.
+        self.related_by_senders = self.filter_json.get("related_by_senders", None)
+        self.related_by_rel_types = self.filter_json.get("related_by_rel_types", None)
+
+        # Fallback to the unstable prefix if the stable version is not given.
         if hs.config.experimental.msc3440_enabled:
-            self.relation_senders = self.filter_json.get(
+            self.related_by_senders = self.related_by_senders or self.filter_json.get(
                 "io.element.relation_senders", None
             )
-            self.relation_types = self.filter_json.get(
-                "io.element.relation_types", None
+            self.related_by_rel_types = (
+                self.related_by_rel_types
+                or self.filter_json.get("io.element.relation_types", None)
             )
-        else:
-            self.relation_senders = None
-            self.relation_types = None
 
     def filters_all_types(self) -> bool:
         return "*" in self.not_types
@@ -461,7 +462,7 @@ async def _check_event_relations(
         event_ids = [event.event_id for event in events if isinstance(event, EventBase)]  # type: ignore[attr-defined]
         event_ids_to_keep = set(
             await self._store.events_have_relations(
-                event_ids, self.relation_senders, self.relation_types
+                event_ids, self.related_by_senders, self.related_by_rel_types
             )
         )
 
@@ -474,7 +475,7 @@ async def _check_event_relations(
     async def filter(self, events: Iterable[FilterEvent]) -> List[FilterEvent]:
         result = [event for event in events if self._check(event)]
 
-        if self.relation_senders or self.relation_types:
+        if self.related_by_senders or self.related_by_rel_types:
             return await self._check_event_relations(result)
 
         return result
diff --git a/synapse/app/generic_worker.py b/synapse/app/generic_worker.py
index 1536a4272333..b6f510ed3058 100644
--- a/synapse/app/generic_worker.py
+++ b/synapse/app/generic_worker.py
@@ -322,7 +322,8 @@ def _listen_http(self, listener_config: ListenerConfig) -> None:
 
                     presence.register_servlets(self, resource)
 
-                    groups.register_servlets(self, resource)
+                    if self.config.experimental.groups_enabled:
+                        groups.register_servlets(self, resource)
 
                     resources.update({CLIENT_API_PREFIX: resource})
 
@@ -417,7 +418,7 @@ def start_listening(self) -> None:
             else:
                 logger.warning("Unsupported listener type: %s", listener.type)
 
-        self.get_tcp_replication().start_replication(self)
+        self.get_replication_command_handler().start_replication(self)
 
 
 def start(config_options: List[str]) -> None:
diff --git a/synapse/app/homeserver.py b/synapse/app/homeserver.py
index a6789a840ede..e4dc04c0b40f 100644
--- a/synapse/app/homeserver.py
+++ b/synapse/app/homeserver.py
@@ -273,7 +273,7 @@ def start_listening(self) -> None:
             # If redis is enabled we connect via the replication command handler
             # in the same way as the workers (since we're effectively a client
             # rather than a server).
-            self.get_tcp_replication().start_replication(self)
+            self.get_replication_command_handler().start_replication(self)
 
         for listener in self.config.server.listeners:
             if listener.type == "http":
diff --git a/synapse/appservice/__init__.py b/synapse/appservice/__init__.py
index 87f36531f454..caf9014540fb 100644
--- a/synapse/appservice/__init__.py
+++ b/synapse/appservice/__init__.py
@@ -175,27 +175,14 @@ def _is_exclusive(self, namespace_key: str, test_string: str) -> bool:
             return namespace.exclusive
         return False
 
-    async def _matches_user(self, event: EventBase, store: "DataStore") -> bool:
-        if self.is_interested_in_user(event.sender):
-            return True
-
-        # also check m.room.member state key
-        if event.type == EventTypes.Member and self.is_interested_in_user(
-            event.state_key
-        ):
-            return True
-
-        does_match = await self.matches_user_in_member_list(event.room_id, store)
-        return does_match
-
     @cached(num_args=1, cache_context=True)
-    async def matches_user_in_member_list(
+    async def _matches_user_in_member_list(
         self,
         room_id: str,
         store: "DataStore",
         cache_context: _CacheContext,
     ) -> bool:
-        """Check if this service is interested a room based upon it's membership
+        """Check if this service is interested a room based upon its membership
 
         Args:
             room_id: The room to check.
@@ -214,52 +201,115 @@ async def matches_user_in_member_list(
                 return True
         return False
 
-    def _matches_room_id(self, event: EventBase) -> bool:
-        if hasattr(event, "room_id"):
-            return self.is_interested_in_room(event.room_id)
-        return False
+    def is_interested_in_user(
+        self,
+        user_id: str,
+    ) -> bool:
+        """
+        Returns whether the application is interested in a given user ID.
+
+        The appservice is considered to be interested in a user if either: the
+        user ID is in the appservice's user namespace, or if the user is the
+        appservice's configured sender_localpart.
+
+        Args:
+            user_id: The ID of the user to check.
+
+        Returns:
+            True if the application service is interested in the user, False if not.
+        """
+        return (
+            # User is the appservice's sender_localpart user
+            user_id == self.sender
+            # User is in the appservice's user namespace
+            or self.is_user_in_namespace(user_id)
+        )
+
+    @cached(num_args=1, cache_context=True)
+    async def is_interested_in_room(
+        self,
+        room_id: str,
+        store: "DataStore",
+        cache_context: _CacheContext,
+    ) -> bool:
+        """
+        Returns whether the application service is interested in a given room ID.
+
+        The appservice is considered to be interested in the room if either: the ID or one
+        of the aliases of the room is in the appservice's room ID or alias namespace
+        respectively, or if one of the members of the room fall into the appservice's user
+        namespace.
+
+        Args:
+            room_id: The ID of the room to check.
+            store: The homeserver's datastore class.
+
+        Returns:
+            True if the application service is interested in the room, False if not.
+        """
+        # Check if we have interest in this room ID
+        if self.is_room_id_in_namespace(room_id):
+            return True
 
-    async def _matches_aliases(self, event: EventBase, store: "DataStore") -> bool:
-        alias_list = await store.get_aliases_for_room(event.room_id)
+        # likewise with the room's aliases (if it has any)
+        alias_list = await store.get_aliases_for_room(room_id)
         for alias in alias_list:
-            if self.is_interested_in_alias(alias):
+            if self.is_room_alias_in_namespace(alias):
                 return True
 
-        return False
+        # And finally, perform an expensive check on whether any of the
+        # users in the room match the appservice's user namespace
+        return await self._matches_user_in_member_list(
+            room_id, store, on_invalidate=cache_context.invalidate
+        )
 
-    async def is_interested(self, event: EventBase, store: "DataStore") -> bool:
+    @cached(num_args=1, cache_context=True)
+    async def is_interested_in_event(
+        self,
+        event_id: str,
+        event: EventBase,
+        store: "DataStore",
+        cache_context: _CacheContext,
+    ) -> bool:
         """Check if this service is interested in this event.
 
         Args:
+            event_id: The ID of the event to check. This is purely used for simplifying the
+                caching of calls to this method.
             event: The event to check.
             store: The datastore to query.
 
         Returns:
-            True if this service would like to know about this event.
+            True if this service would like to know about this event, otherwise False.
         """
-        # Do cheap checks first
-        if self._matches_room_id(event):
-            return True
-
         # Beeper Hack
         # Don't bother sending events for bridged users, the bridge presumably already knows this happened.
         if event and event.sender.startswith("@_"):
             return False
 
-        # This will check the namespaces first before
-        # checking the store, so should be run before _matches_aliases
-        if await self._matches_user(event, store):
+        # Check if we're interested in this event's sender by namespace (or if they're the
+        # sender_localpart user)
+        if self.is_interested_in_user(event.sender):
+            return True
+
+        # additionally, if this is a membership event, perform the same checks on
+        # the user it references
+        if event.type == EventTypes.Member and self.is_interested_in_user(
+            event.state_key
+        ):
             return True
 
-        # This will check the store, so should be run last
-        if await self._matches_aliases(event, store):
+        # This will check the datastore, so should be run last
+        if await self.is_interested_in_room(
+            event.room_id, store, on_invalidate=cache_context.invalidate
+        ):
             return True
 
         return False
 
-    @cached(num_args=1)
+    @cached(num_args=1, cache_context=True)
     async def is_interested_in_presence(
-        self, user_id: UserID, store: "DataStore"
+        self, user_id: UserID, store: "DataStore", cache_context: _CacheContext
     ) -> bool:
         """Check if this service is interested a user's presence
 
@@ -277,20 +327,19 @@ async def is_interested_in_presence(
 
         # Then find out if the appservice is interested in any of those rooms
         for room_id in room_ids:
-            if await self.matches_user_in_member_list(room_id, store):
+            if await self.is_interested_in_room(
+                room_id, store, on_invalidate=cache_context.invalidate
+            ):
                 return True
         return False
 
-    def is_interested_in_user(self, user_id: str) -> bool:
-        return (
-            bool(self._matches_regex(ApplicationService.NS_USERS, user_id))
-            or user_id == self.sender
-        )
+    def is_user_in_namespace(self, user_id: str) -> bool:
+        return bool(self._matches_regex(ApplicationService.NS_USERS, user_id))
 
-    def is_interested_in_alias(self, alias: str) -> bool:
+    def is_room_alias_in_namespace(self, alias: str) -> bool:
         return bool(self._matches_regex(ApplicationService.NS_ALIASES, alias))
 
-    def is_interested_in_room(self, room_id: str) -> bool:
+    def is_room_id_in_namespace(self, room_id: str) -> bool:
         return bool(self._matches_regex(ApplicationService.NS_ROOMS, room_id))
 
     def is_exclusive_user(self, user_id: str) -> bool:
diff --git a/synapse/appservice/api.py b/synapse/appservice/api.py
index a0ea958af62a..98fe354014c4 100644
--- a/synapse/appservice/api.py
+++ b/synapse/appservice/api.py
@@ -25,7 +25,7 @@
     TransactionUnusedFallbackKeys,
 )
 from synapse.events import EventBase
-from synapse.events.utils import serialize_event
+from synapse.events.utils import SerializeEventConfig, serialize_event
 from synapse.http.client import SimpleHttpClient
 from synapse.types import JsonDict, ThirdPartyInstanceID
 from synapse.util.caches.response_cache import ResponseCache
@@ -321,16 +321,18 @@ def _serialize(
             serialize_event(
                 e,
                 time_now,
-                as_client_event=True,
-                # If this is an invite or a knock membership event, and we're interested
-                # in this user, then include any stripped state alongside the event.
-                include_stripped_room_state=(
-                    e.type == EventTypes.Member
-                    and (
-                        e.membership == Membership.INVITE
-                        or e.membership == Membership.KNOCK
-                    )
-                    and service.is_interested_in_user(e.state_key)
+                config=SerializeEventConfig(
+                    as_client_event=True,
+                    # If this is an invite or a knock membership event, and we're interested
+                    # in this user, then include any stripped state alongside the event.
+                    include_stripped_room_state=(
+                        e.type == EventTypes.Member
+                        and (
+                            e.membership == Membership.INVITE
+                            or e.membership == Membership.KNOCK
+                        )
+                        and service.is_interested_in_user(e.state_key)
+                    ),
                 ),
             )
             for e in events
diff --git a/synapse/config/_base.py b/synapse/config/_base.py
index 1265738dc12e..8e19e2fc2668 100644
--- a/synapse/config/_base.py
+++ b/synapse/config/_base.py
@@ -383,7 +383,7 @@ def generate_config(
         Build a default configuration file
 
         This is used when the user explicitly asks us to generate a config file
-        (eg with --generate_config).
+        (eg with --generate-config).
 
         Args:
             config_dir_path: The path where the config files are kept. Used to
diff --git a/synapse/config/_base.pyi b/synapse/config/_base.pyi
index 1eb5f5a68cf8..363d8b45545e 100644
--- a/synapse/config/_base.pyi
+++ b/synapse/config/_base.pyi
@@ -19,6 +19,7 @@ from synapse.config import (
     api,
     appservice,
     auth,
+    background_updates,
     cache,
     captcha,
     cas,
@@ -113,6 +114,7 @@ class RootConfig:
     caches: cache.CacheConfig
     federation: federation.FederationConfig
     retention: retention.RetentionConfig
+    background_updates: background_updates.BackgroundUpdateConfig
 
     config_classes: List[Type["Config"]] = ...
     def __init__(self) -> None: ...
diff --git a/synapse/config/background_updates.py b/synapse/config/background_updates.py
new file mode 100644
index 000000000000..f6cdeacc4b19
--- /dev/null
+++ b/synapse/config/background_updates.py
@@ -0,0 +1,68 @@
+# Copyright 2022 Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from ._base import Config
+
+
+class BackgroundUpdateConfig(Config):
+    section = "background_updates"
+
+    def generate_config_section(self, **kwargs) -> str:
+        return """\
+        ## Background Updates ##
+
+        # Background updates are database updates that are run in the background in batches.
+        # The duration, minimum batch size, default batch size, whether to sleep between batches and if so, how long to
+        # sleep can all be configured. This is helpful to speed up or slow down the updates.
+        #
+        background_updates:
+            # How long in milliseconds to run a batch of background updates for. Defaults to 100. Uncomment and set
+            # a time to change the default.
+            #
+            #background_update_duration_ms: 500
+
+            # Whether to sleep between updates. Defaults to True. Uncomment to change the default.
+            #
+            #sleep_enabled: false
+
+            # If sleeping between updates, how long in milliseconds to sleep for. Defaults to 1000. Uncomment
+            # and set a duration to change the default.
+            #
+            #sleep_duration_ms: 300
+
+            # Minimum size a batch of background updates can be. Must be greater than 0. Defaults to 1. Uncomment and
+            # set a size to change the default.
+            #
+            #min_batch_size: 10
+
+            # The batch size to use for the first iteration of a new background update. The default is 100.
+            # Uncomment and set a size to change the default.
+            #
+            #default_batch_size: 50
+        """
+
+    def read_config(self, config, **kwargs) -> None:
+        bg_update_config = config.get("background_updates") or {}
+
+        self.update_duration_ms = bg_update_config.get(
+            "background_update_duration_ms", 100
+        )
+
+        self.sleep_enabled = bg_update_config.get("sleep_enabled", True)
+
+        self.sleep_duration_ms = bg_update_config.get("sleep_duration_ms", 1000)
+
+        self.min_batch_size = bg_update_config.get("min_batch_size", 1)
+
+        self.default_batch_size = bg_update_config.get("default_batch_size", 100)
diff --git a/synapse/config/experimental.py b/synapse/config/experimental.py
index 61efa01d7869..8e4a00ec1ced 100644
--- a/synapse/config/experimental.py
+++ b/synapse/config/experimental.py
@@ -76,3 +76,6 @@ def read_config(self, config: JsonDict, **kwargs):
 
         # MSC3720 (Account status endpoint)
         self.msc3720_enabled: bool = experimental.get("msc3720_enabled", False)
+
+        # The deprecated groups feature.
+        self.groups_enabled: bool = experimental.get("groups_enabled", True)
diff --git a/synapse/config/homeserver.py b/synapse/config/homeserver.py
index 001605c265fb..a4ec70690802 100644
--- a/synapse/config/homeserver.py
+++ b/synapse/config/homeserver.py
@@ -16,6 +16,7 @@
 from .api import ApiConfig
 from .appservice import AppServiceConfig
 from .auth import AuthConfig
+from .background_updates import BackgroundUpdateConfig
 from .cache import CacheConfig
 from .captcha import CaptchaConfig
 from .cas import CasConfig
@@ -99,4 +100,5 @@ class HomeServerConfig(RootConfig):
         WorkerConfig,
         RedisConfig,
         ExperimentalConfig,
+        BackgroundUpdateConfig,
     ]
diff --git a/synapse/config/oidc.py b/synapse/config/oidc.py
index f7e4f9ef22b1..5d571651cbc9 100644
--- a/synapse/config/oidc.py
+++ b/synapse/config/oidc.py
@@ -182,8 +182,14 @@ def generate_config_section(self, config_dir_path, server_name, **kwargs) -> str
         #
         #             localpart_template: Jinja2 template for the localpart of the MXID.
         #                 If this is not set, the user will be prompted to choose their
-        #                 own username (see 'sso_auth_account_details.html' in the 'sso'
-        #                 section of this file).
+        #                 own username (see the documentation for the
+        #                 'sso_auth_account_details.html' template). This template can
+        #                 use the 'localpart_from_email' filter.
+        #
+        #             confirm_localpart: Whether to prompt the user to validate (or
+        #                 change) the generated localpart (see the documentation for the
+        #                 'sso_auth_account_details.html' template), instead of
+        #                 registering the account right away.
         #
         #             display_name_template: Jinja2 template for the display name to set
         #                 on first login. If unset, no displayname will be set.
diff --git a/synapse/events/spamcheck.py b/synapse/events/spamcheck.py
index 04afd48274e1..60904a55f5c0 100644
--- a/synapse/events/spamcheck.py
+++ b/synapse/events/spamcheck.py
@@ -245,8 +245,8 @@ async def check_event_for_spam(
         """Checks if a given event is considered "spammy" by this server.
 
         If the server considers an event spammy, then it will be rejected if
-        sent by a local user. If it is sent by a user on another server, then
-        users receive a blank event.
+        sent by a local user. If it is sent by a user on another server, the
+        event is soft-failed.
 
         Args:
             event: the event to be checked
diff --git a/synapse/events/third_party_rules.py b/synapse/events/third_party_rules.py
index ede72ee87631..bfca454f510d 100644
--- a/synapse/events/third_party_rules.py
+++ b/synapse/events/third_party_rules.py
@@ -38,6 +38,8 @@
     [str, StateMap[EventBase], str], Awaitable[bool]
 ]
 ON_NEW_EVENT_CALLBACK = Callable[[EventBase, StateMap[EventBase]], Awaitable]
+CHECK_CAN_SHUTDOWN_ROOM_CALLBACK = Callable[[str, str], Awaitable[bool]]
+CHECK_CAN_DEACTIVATE_USER_CALLBACK = Callable[[str, bool], Awaitable[bool]]
 ON_PROFILE_UPDATE_CALLBACK = Callable[[str, ProfileInfo, bool, bool], Awaitable]
 ON_USER_DEACTIVATION_STATUS_CHANGED_CALLBACK = Callable[[str, bool, bool], Awaitable]
 
@@ -157,6 +159,12 @@ def __init__(self, hs: "HomeServer"):
             CHECK_VISIBILITY_CAN_BE_MODIFIED_CALLBACK
         ] = []
         self._on_new_event_callbacks: List[ON_NEW_EVENT_CALLBACK] = []
+        self._check_can_shutdown_room_callbacks: List[
+            CHECK_CAN_SHUTDOWN_ROOM_CALLBACK
+        ] = []
+        self._check_can_deactivate_user_callbacks: List[
+            CHECK_CAN_DEACTIVATE_USER_CALLBACK
+        ] = []
         self._on_profile_update_callbacks: List[ON_PROFILE_UPDATE_CALLBACK] = []
         self._on_user_deactivation_status_changed_callbacks: List[
             ON_USER_DEACTIVATION_STATUS_CHANGED_CALLBACK
@@ -173,6 +181,8 @@ def register_third_party_rules_callbacks(
             CHECK_VISIBILITY_CAN_BE_MODIFIED_CALLBACK
         ] = None,
         on_new_event: Optional[ON_NEW_EVENT_CALLBACK] = None,
+        check_can_shutdown_room: Optional[CHECK_CAN_SHUTDOWN_ROOM_CALLBACK] = None,
+        check_can_deactivate_user: Optional[CHECK_CAN_DEACTIVATE_USER_CALLBACK] = None,
         on_profile_update: Optional[ON_PROFILE_UPDATE_CALLBACK] = None,
         on_user_deactivation_status_changed: Optional[
             ON_USER_DEACTIVATION_STATUS_CHANGED_CALLBACK
@@ -198,6 +208,11 @@ def register_third_party_rules_callbacks(
         if on_new_event is not None:
             self._on_new_event_callbacks.append(on_new_event)
 
+        if check_can_shutdown_room is not None:
+            self._check_can_shutdown_room_callbacks.append(check_can_shutdown_room)
+
+        if check_can_deactivate_user is not None:
+            self._check_can_deactivate_user_callbacks.append(check_can_deactivate_user)
         if on_profile_update is not None:
             self._on_profile_update_callbacks.append(on_profile_update)
 
@@ -369,6 +384,46 @@ async def on_new_event(self, event_id: str) -> None:
                     "Failed to run module API callback %s: %s", callback, e
                 )
 
+    async def check_can_shutdown_room(self, user_id: str, room_id: str) -> bool:
+        """Intercept requests to shutdown a room. If `False` is returned, the
+         room must not be shut down.
+
+        Args:
+            requester: The ID of the user requesting the shutdown.
+            room_id: The ID of the room.
+        """
+        for callback in self._check_can_shutdown_room_callbacks:
+            try:
+                if await callback(user_id, room_id) is False:
+                    return False
+            except Exception as e:
+                logger.exception(
+                    "Failed to run module API callback %s: %s", callback, e
+                )
+        return True
+
+    async def check_can_deactivate_user(
+        self,
+        user_id: str,
+        by_admin: bool,
+    ) -> bool:
+        """Intercept requests to deactivate a user. If `False` is returned, the
+        user should not be deactivated.
+
+        Args:
+            requester
+            user_id: The ID of the room.
+        """
+        for callback in self._check_can_deactivate_user_callbacks:
+            try:
+                if await callback(user_id, by_admin) is False:
+                    return False
+            except Exception as e:
+                logger.exception(
+                    "Failed to run module API callback %s: %s", callback, e
+                )
+        return True
+
     async def _get_state_map_for_room(self, room_id: str) -> StateMap[EventBase]:
         """Given a room ID, return the state events of that room.
 
diff --git a/synapse/events/utils.py b/synapse/events/utils.py
index 9386fa29ddd3..a0520068e0f9 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -26,6 +26,7 @@
     Union,
 )
 
+import attr
 from frozendict import frozendict
 
 from synapse.api.constants import EventContentFields, EventTypes, RelationTypes
@@ -37,6 +38,7 @@
 from . import EventBase
 
 if TYPE_CHECKING:
+    from synapse.server import HomeServer
     from synapse.storage.databases.main.relations import BundledAggregations
 
 
@@ -303,29 +305,37 @@ def format_event_for_client_v2_without_room_id(d: JsonDict) -> JsonDict:
     return d
 
 
+@attr.s(slots=True, frozen=True, auto_attribs=True)
+class SerializeEventConfig:
+    as_client_event: bool = True
+    # Function to convert from federation format to client format
+    event_format: Callable[[JsonDict], JsonDict] = format_event_for_client_v1
+    # ID of the user's auth token - used for namespacing of transaction IDs
+    token_id: Optional[int] = None
+    # List of event fields to include. If empty, all fields will be returned.
+    only_event_fields: Optional[List[str]] = None
+    # Some events can have stripped room state stored in the `unsigned` field.
+    # This is required for invite and knock functionality. If this option is
+    # False, that state will be removed from the event before it is returned.
+    # Otherwise, it will be kept.
+    include_stripped_room_state: bool = False
+
+
+_DEFAULT_SERIALIZE_EVENT_CONFIG = SerializeEventConfig()
+
+
 def serialize_event(
     e: Union[JsonDict, EventBase],
     time_now_ms: int,
     *,
-    as_client_event: bool = True,
-    event_format: Callable[[JsonDict], JsonDict] = format_event_for_client_v1,
-    token_id: Optional[str] = None,
-    only_event_fields: Optional[List[str]] = None,
-    include_stripped_room_state: bool = False,
+    config: SerializeEventConfig = _DEFAULT_SERIALIZE_EVENT_CONFIG,
 ) -> JsonDict:
     """Serialize event for clients
 
     Args:
         e
         time_now_ms
-        as_client_event
-        event_format
-        token_id
-        only_event_fields
-        include_stripped_room_state: Some events can have stripped room state
-            stored in the `unsigned` field. This is required for invite and knock
-            functionality. If this option is False, that state will be removed from the
-            event before it is returned. Otherwise, it will be kept.
+        config: Event serialization config
 
     Returns:
         The serialized event dictionary.
@@ -348,11 +358,11 @@ def serialize_event(
 
     if "redacted_because" in e.unsigned:
         d["unsigned"]["redacted_because"] = serialize_event(
-            e.unsigned["redacted_because"], time_now_ms, event_format=event_format
+            e.unsigned["redacted_because"], time_now_ms, config=config
         )
 
-    if token_id is not None:
-        if token_id == getattr(e.internal_metadata, "token_id", None):
+    if config.token_id is not None:
+        if config.token_id == getattr(e.internal_metadata, "token_id", None):
             txn_id = getattr(e.internal_metadata, "txn_id", None)
             if txn_id is not None:
                 d["unsigned"]["transaction_id"] = txn_id
@@ -361,13 +371,14 @@ def serialize_event(
     # that are meant to provide metadata about a room to an invitee/knocker. They are
     # intended to only be included in specific circumstances, such as down sync, and
     # should not be included in any other case.
-    if not include_stripped_room_state:
+    if not config.include_stripped_room_state:
         d["unsigned"].pop("invite_room_state", None)
         d["unsigned"].pop("knock_room_state", None)
 
-    if as_client_event:
-        d = event_format(d)
+    if config.as_client_event:
+        d = config.event_format(d)
 
+    only_event_fields = config.only_event_fields
     if only_event_fields:
         if not isinstance(only_event_fields, list) or not all(
             isinstance(f, str) for f in only_event_fields
@@ -385,23 +396,26 @@ class EventClientSerializer:
     clients.
     """
 
+    def __init__(self, hs: "HomeServer"):
+        self._msc3440_enabled = hs.config.experimental.msc3440_enabled
+
     def serialize_event(
         self,
         event: Union[JsonDict, EventBase],
         time_now: int,
         *,
+        config: SerializeEventConfig = _DEFAULT_SERIALIZE_EVENT_CONFIG,
         bundle_aggregations: Optional[Dict[str, "BundledAggregations"]] = None,
-        **kwargs: Any,
     ) -> JsonDict:
         """Serializes a single event.
 
         Args:
             event: The event being serialized.
             time_now: The current time in milliseconds
+            config: Event serialization config
             bundle_aggregations: Whether to include the bundled aggregations for this
                 event. Only applies to non-state events. (State events never include
                 bundled aggregations.)
-            **kwargs: Arguments to pass to `serialize_event`
 
         Returns:
             The serialized event
@@ -410,7 +424,7 @@ def serialize_event(
         if not isinstance(event, EventBase):
             return event
 
-        serialized_event = serialize_event(event, time_now, **kwargs)
+        serialized_event = serialize_event(event, time_now, config=config)
 
         # Check if there are any bundled aggregations to include with the event.
         if bundle_aggregations:
@@ -419,6 +433,7 @@ def serialize_event(
                 self._inject_bundled_aggregations(
                     event,
                     time_now,
+                    config,
                     bundle_aggregations[event.event_id],
                     serialized_event,
                 )
@@ -456,6 +471,7 @@ def _inject_bundled_aggregations(
         self,
         event: EventBase,
         time_now: int,
+        config: SerializeEventConfig,
         aggregations: "BundledAggregations",
         serialized_event: JsonDict,
     ) -> None:
@@ -466,6 +482,7 @@ def _inject_bundled_aggregations(
             time_now: The current time in milliseconds
             aggregations: The bundled aggregation to serialize.
             serialized_event: The serialized event which may be modified.
+            config: Event serialization config
 
         """
         serialized_aggregations = {}
@@ -493,8 +510,8 @@ def _inject_bundled_aggregations(
             thread = aggregations.thread
 
             # Don't bundle aggregations as this could recurse forever.
-            serialized_latest_event = self.serialize_event(
-                thread.latest_event, time_now, bundle_aggregations=None
+            serialized_latest_event = serialize_event(
+                thread.latest_event, time_now, config=config
             )
             # Manually apply an edit, if one exists.
             if thread.latest_edit:
@@ -502,33 +519,53 @@ def _inject_bundled_aggregations(
                     thread.latest_event, serialized_latest_event, thread.latest_edit
                 )
 
-            serialized_aggregations[RelationTypes.THREAD] = {
+            thread_summary = {
                 "latest_event": serialized_latest_event,
                 "count": thread.count,
                 "current_user_participated": thread.current_user_participated,
             }
+            serialized_aggregations[RelationTypes.THREAD] = thread_summary
+            if self._msc3440_enabled:
+                serialized_aggregations[RelationTypes.UNSTABLE_THREAD] = thread_summary
 
         # Include the bundled aggregations in the event.
         if serialized_aggregations:
-            serialized_event["unsigned"].setdefault("m.relations", {}).update(
-                serialized_aggregations
-            )
+            # There is likely already an "unsigned" field, but a filter might
+            # have stripped it off (via the event_fields option). The server is
+            # allowed to return additional fields, so add it back.
+            serialized_event.setdefault("unsigned", {}).setdefault(
+                "m.relations", {}
+            ).update(serialized_aggregations)
 
     def serialize_events(
-        self, events: Iterable[Union[JsonDict, EventBase]], time_now: int, **kwargs: Any
+        self,
+        events: Iterable[Union[JsonDict, EventBase]],
+        time_now: int,
+        *,
+        config: SerializeEventConfig = _DEFAULT_SERIALIZE_EVENT_CONFIG,
+        bundle_aggregations: Optional[Dict[str, "BundledAggregations"]] = None,
     ) -> List[JsonDict]:
         """Serializes multiple events.
 
         Args:
             event
             time_now: The current time in milliseconds
-            **kwargs: Arguments to pass to `serialize_event`
+            config: Event serialization config
+            bundle_aggregations: Whether to include the bundled aggregations for this
+                event. Only applies to non-state events. (State events never include
+                bundled aggregations.)
 
         Returns:
             The list of serialized events
         """
         return [
-            self.serialize_event(event, time_now=time_now, **kwargs) for event in events
+            self.serialize_event(
+                event,
+                time_now,
+                config=config,
+                bundle_aggregations=bundle_aggregations,
+            )
+            for event in events
         ]
 
 
diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py
index 64e595e748f4..467275b98c3c 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -1428,7 +1428,7 @@ async def send_request(
 
             # Validate children_state of the room.
             children_state = room.pop("children_state", [])
-            if not isinstance(children_state, Sequence):
+            if not isinstance(children_state, list):
                 raise InvalidResponseError("'room.children_state' must be a list")
             if any(not isinstance(e, dict) for e in children_state):
                 raise InvalidResponseError("Invalid event in 'children_state' list")
@@ -1440,14 +1440,14 @@ async def send_request(
 
             # Validate the children rooms.
             children = res.get("children", [])
-            if not isinstance(children, Sequence):
+            if not isinstance(children, list):
                 raise InvalidResponseError("'children' must be a list")
             if any(not isinstance(r, dict) for r in children):
                 raise InvalidResponseError("Invalid room in 'children' list")
 
             # Validate the inaccessible children.
             inaccessible_children = res.get("inaccessible_children", [])
-            if not isinstance(inaccessible_children, Sequence):
+            if not isinstance(inaccessible_children, list):
                 raise InvalidResponseError("'inaccessible_children' must be a list")
             if any(not isinstance(r, str) for r in inaccessible_children):
                 raise InvalidResponseError(
@@ -1630,7 +1630,7 @@ def _validate_hierarchy_event(d: JsonDict) -> None:
         raise ValueError("Invalid event: 'content' must be a dict")
 
     via = content.get("via")
-    if not isinstance(via, Sequence):
+    if not isinstance(via, list):
         raise ValueError("Invalid event: 'via' must be a list")
     if any(not isinstance(v, str) for v in via):
         raise ValueError("Invalid event: 'via' must be a list of strings")
diff --git a/synapse/federation/send_queue.py b/synapse/federation/send_queue.py
index 0d7c4f506758..d720b5fd3fe2 100644
--- a/synapse/federation/send_queue.py
+++ b/synapse/federation/send_queue.py
@@ -244,7 +244,7 @@ def send_presence_to_destinations(
 
         self.notifier.on_new_replication_data()
 
-    def send_device_messages(self, destination: str) -> None:
+    def send_device_messages(self, destination: str, immediate: bool = False) -> None:
         """As per FederationSender"""
         # We don't need to replicate this as it gets sent down a different
         # stream.
diff --git a/synapse/federation/sender/__init__.py b/synapse/federation/sender/__init__.py
index 6106a486d10a..30e2421efc6d 100644
--- a/synapse/federation/sender/__init__.py
+++ b/synapse/federation/sender/__init__.py
@@ -118,7 +118,12 @@ def build_and_send_edu(
         raise NotImplementedError()
 
     @abc.abstractmethod
-    def send_device_messages(self, destination: str) -> None:
+    def send_device_messages(self, destination: str, immediate: bool = True) -> None:
+        """Tells the sender that a new device message is ready to be sent to the
+        destination. The `immediate` flag specifies whether the messages should
+        be tried to be sent immediately, or whether it can be delayed for a
+        short while (to aid performance).
+        """
         raise NotImplementedError()
 
     @abc.abstractmethod
@@ -146,9 +151,8 @@ async def get_replication_rows(
 
 
 @attr.s
-class _PresenceQueue:
-    """A queue of destinations that need to be woken up due to new presence
-    updates.
+class _DestinationWakeupQueue:
+    """A queue of destinations that need to be woken up due to new updates.
 
     Staggers waking up of per destination queues to ensure that we don't attempt
     to start TLS connections with many hosts all at once, leading to pinned CPU.
@@ -175,7 +179,7 @@ def add_to_queue(self, destination: str) -> None:
         if not self.processing:
             self._handle()
 
-    @wrap_as_background_process("_PresenceQueue.handle")
+    @wrap_as_background_process("_DestinationWakeupQueue.handle")
     async def _handle(self) -> None:
         """Background process to drain the queue."""
 
@@ -297,7 +301,7 @@ def __init__(self, hs: "HomeServer"):
 
         self._external_cache = hs.get_external_cache()
 
-        self._presence_queue = _PresenceQueue(self, self.clock)
+        self._destination_wakeup_queue = _DestinationWakeupQueue(self, self.clock)
 
     def _get_per_destination_queue(self, destination: str) -> PerDestinationQueue:
         """Get or create a PerDestinationQueue for the given destination
@@ -614,7 +618,7 @@ def send_presence_to_destinations(
                 states, start_loop=False
             )
 
-            self._presence_queue.add_to_queue(destination)
+            self._destination_wakeup_queue.add_to_queue(destination)
 
     def build_and_send_edu(
         self,
@@ -667,7 +671,7 @@ def send_edu(self, edu: Edu, key: Optional[Hashable]) -> None:
         else:
             queue.send_edu(edu)
 
-    def send_device_messages(self, destination: str) -> None:
+    def send_device_messages(self, destination: str, immediate: bool = False) -> None:
         if destination == self.server_name:
             logger.warning("Not sending device update to ourselves")
             return
@@ -677,7 +681,11 @@ def send_device_messages(self, destination: str) -> None:
         ):
             return
 
-        self._get_per_destination_queue(destination).attempt_new_transaction()
+        if immediate:
+            self._get_per_destination_queue(destination).attempt_new_transaction()
+        else:
+            self._get_per_destination_queue(destination).mark_new_data()
+            self._destination_wakeup_queue.add_to_queue(destination)
 
     def wake_destination(self, destination: str) -> None:
         """Called when we want to retry sending transactions to a remote.
diff --git a/synapse/federation/sender/per_destination_queue.py b/synapse/federation/sender/per_destination_queue.py
index c8768f22bc6b..d80f0ac5e8c3 100644
--- a/synapse/federation/sender/per_destination_queue.py
+++ b/synapse/federation/sender/per_destination_queue.py
@@ -219,6 +219,16 @@ def send_edu(self, edu: Edu) -> None:
         self._pending_edus.append(edu)
         self.attempt_new_transaction()
 
+    def mark_new_data(self) -> None:
+        """Marks that the destination has new data to send, without starting a
+        new transaction.
+
+        If a transaction loop is already in progress then a new transcation will
+        be attempted when the current one finishes.
+        """
+
+        self._new_data_to_send = True
+
     def attempt_new_transaction(self) -> None:
         """Try to start a new transaction to this destination
 
diff --git a/synapse/federation/transport/server/__init__.py b/synapse/federation/transport/server/__init__.py
index 67a634790712..71b2f90eb920 100644
--- a/synapse/federation/transport/server/__init__.py
+++ b/synapse/federation/transport/server/__init__.py
@@ -289,7 +289,7 @@ async def on_GET(
         return 200, {"sub": user_id}
 
 
-DEFAULT_SERVLET_GROUPS: Dict[str, Iterable[Type[BaseFederationServlet]]] = {
+SERVLET_GROUPS: Dict[str, Iterable[Type[BaseFederationServlet]]] = {
     "federation": FEDERATION_SERVLET_CLASSES,
     "room_list": (PublicRoomList,),
     "group_server": GROUP_SERVER_SERVLET_CLASSES,
@@ -298,6 +298,10 @@ async def on_GET(
     "openid": (OpenIdUserInfo,),
 }
 
+DEFAULT_SERVLET_GROUPS = ("federation", "room_list", "openid")
+
+GROUP_SERVLET_GROUPS = ("group_server", "group_local", "group_attestation")
+
 
 def register_servlets(
     hs: "HomeServer",
@@ -320,16 +324,19 @@ def register_servlets(
             Defaults to ``DEFAULT_SERVLET_GROUPS``.
     """
     if not servlet_groups:
-        servlet_groups = DEFAULT_SERVLET_GROUPS.keys()
+        servlet_groups = DEFAULT_SERVLET_GROUPS
+        # Only allow the groups servlets if the deprecated groups feature is enabled.
+        if hs.config.experimental.groups_enabled:
+            servlet_groups = servlet_groups + GROUP_SERVLET_GROUPS
 
     for servlet_group in servlet_groups:
         # Skip unknown servlet groups.
-        if servlet_group not in DEFAULT_SERVLET_GROUPS:
+        if servlet_group not in SERVLET_GROUPS:
             raise RuntimeError(
                 f"Attempting to register unknown federation servlet: '{servlet_group}'"
             )
 
-        for servletclass in DEFAULT_SERVLET_GROUPS[servlet_group]:
+        for servletclass in SERVLET_GROUPS[servlet_group]:
             # Only allow the `/timestamp_to_event` servlet if msc3030 is enabled
             if (
                 servletclass == FederationTimestampLookupServlet
diff --git a/synapse/federation/transport/server/_base.py b/synapse/federation/transport/server/_base.py
index 87e99c7ddf5b..2529dee613aa 100644
--- a/synapse/federation/transport/server/_base.py
+++ b/synapse/federation/transport/server/_base.py
@@ -63,7 +63,7 @@ def __init__(self, hs: "HomeServer"):
 
         self.replication_client = None
         if hs.config.worker.worker_app:
-            self.replication_client = hs.get_tcp_replication()
+            self.replication_client = hs.get_replication_command_handler()
 
     # A method just so we can pass 'self' as the authenticator to the Servlets
     async def authenticate_request(
diff --git a/synapse/handlers/appservice.py b/synapse/handlers/appservice.py
index e6461cc3c980..bd913e524e7b 100644
--- a/synapse/handlers/appservice.py
+++ b/synapse/handlers/appservice.py
@@ -571,7 +571,7 @@ async def query_room_alias_exists(
         room_alias_str = room_alias.to_string()
         services = self.store.get_app_services()
         alias_query_services = [
-            s for s in services if (s.is_interested_in_alias(room_alias_str))
+            s for s in services if (s.is_room_alias_in_namespace(room_alias_str))
         ]
         for alias_service in alias_query_services:
             is_known_alias = await self.appservice_api.query_alias(
@@ -660,7 +660,7 @@ async def _get_services_for_event(
         # inside of a list comprehension anymore.
         interested_list = []
         for s in services:
-            if await s.is_interested(event, self.store):
+            if await s.is_interested_in_event(event.event_id, event, self.store):
                 interested_list.append(s)
 
         return interested_list
diff --git a/synapse/handlers/deactivate_account.py b/synapse/handlers/deactivate_account.py
index 76ae768e6ef5..816e1a6d79c8 100644
--- a/synapse/handlers/deactivate_account.py
+++ b/synapse/handlers/deactivate_account.py
@@ -17,7 +17,7 @@
 
 from synapse.api.errors import SynapseError
 from synapse.metrics.background_process_metrics import run_as_background_process
-from synapse.types import Requester, UserID, create_requester
+from synapse.types import Codes, Requester, UserID, create_requester
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
@@ -42,6 +42,7 @@ def __init__(self, hs: "HomeServer"):
 
         # Flag that indicates whether the process to part users from rooms is running
         self._user_parter_running = False
+        self._third_party_rules = hs.get_third_party_event_rules()
 
         # Start the user parter loop so it can resume parting users from rooms where
         # it left off (if it has work left to do).
@@ -74,6 +75,15 @@ async def deactivate_account(
         Returns:
             True if identity server supports removing threepids, otherwise False.
         """
+
+        # Check if this user can be deactivated
+        if not await self._third_party_rules.check_can_deactivate_user(
+            user_id, by_admin
+        ):
+            raise SynapseError(
+                403, "Deactivation of this user is forbidden", Codes.FORBIDDEN
+            )
+
         # FIXME: Theoretically there is a race here wherein user resets
         # password using threepid.
 
diff --git a/synapse/handlers/device.py b/synapse/handlers/device.py
index 934b5bd7349b..d5ccaa0c37cc 100644
--- a/synapse/handlers/device.py
+++ b/synapse/handlers/device.py
@@ -371,7 +371,6 @@ async def delete_device(self, user_id: str, device_id: str) -> None:
                 log_kv(
                     {"reason": "User doesn't have device id.", "device_id": device_id}
                 )
-                pass
             else:
                 raise
 
@@ -414,7 +413,6 @@ async def delete_devices(self, user_id: str, device_ids: List[str]) -> None:
                 # no match
                 set_tag("error", True)
                 set_tag("reason", "User doesn't have that device id.")
-                pass
             else:
                 raise
 
@@ -506,7 +504,7 @@ async def notify_device_update(
                 "Sending device list update notif for %r to: %r", user_id, hosts
             )
             for host in hosts:
-                self.federation_sender.send_device_messages(host)
+                self.federation_sender.send_device_messages(host, immediate=False)
                 log_kv({"message": "sent device update to host", "host": host})
 
     async def notify_user_signature_update(
diff --git a/synapse/handlers/directory.py b/synapse/handlers/directory.py
index b7064c6624b7..33d827a45b33 100644
--- a/synapse/handlers/directory.py
+++ b/synapse/handlers/directory.py
@@ -119,7 +119,7 @@ async def create_association(
 
         service = requester.app_service
         if service:
-            if not service.is_interested_in_alias(room_alias_str):
+            if not service.is_room_alias_in_namespace(room_alias_str):
                 raise SynapseError(
                     400,
                     "This application service has not reserved this kind of alias.",
@@ -221,7 +221,7 @@ async def delete_association(
     async def delete_appservice_association(
         self, service: ApplicationService, room_alias: RoomAlias
     ) -> None:
-        if not service.is_interested_in_alias(room_alias.to_string()):
+        if not service.is_room_alias_in_namespace(room_alias.to_string()):
             raise SynapseError(
                 400,
                 "This application service has not reserved this kind of alias",
@@ -376,7 +376,7 @@ def can_modify_alias(self, alias: RoomAlias, user_id: Optional[str] = None) -> b
         # non-exclusive locks on the alias (or there are no interested services)
         services = self.store.get_app_services()
         interested_services = [
-            s for s in services if s.is_interested_in_alias(alias.to_string())
+            s for s in services if s.is_room_alias_in_namespace(alias.to_string())
         ]
 
         for service in interested_services:
diff --git a/synapse/handlers/events.py b/synapse/handlers/events.py
index 97e75e60c32e..d2ccb5c5d311 100644
--- a/synapse/handlers/events.py
+++ b/synapse/handlers/events.py
@@ -19,6 +19,7 @@
 from synapse.api.constants import EduTypes, EventTypes, Membership
 from synapse.api.errors import AuthError, SynapseError
 from synapse.events import EventBase
+from synapse.events.utils import SerializeEventConfig
 from synapse.handlers.presence import format_user_presence_state
 from synapse.streams.config import PaginationConfig
 from synapse.types import JsonDict, UserID
@@ -120,7 +121,7 @@ async def get_stream(
             chunks = self._event_serializer.serialize_events(
                 events,
                 time_now,
-                as_client_event=as_client_event,
+                config=SerializeEventConfig(as_client_event=as_client_event),
             )
 
             chunk = {
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index eb03a5accbac..db39aeabded6 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -23,8 +23,6 @@
 from signedjson.sign import verify_signed_json
 from unpaddedbase64 import decode_base64
 
-from twisted.internet import defer
-
 from synapse import event_auth
 from synapse.api.constants import EventContentFields, EventTypes, Membership
 from synapse.api.errors import (
@@ -45,11 +43,7 @@
 from synapse.events.validator import EventValidator
 from synapse.federation.federation_client import InvalidResponseError
 from synapse.http.servlet import assert_params_in_dict
-from synapse.logging.context import (
-    make_deferred_yieldable,
-    nested_logging_context,
-    preserve_fn,
-)
+from synapse.logging.context import nested_logging_context
 from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.replication.http.federation import (
     ReplicationCleanRoomRestServlet,
@@ -355,56 +349,8 @@ async def try_backfill(domains: List[str]) -> bool:
         if success:
             return True
 
-        # Huh, well *those* domains didn't work out. Lets try some domains
-        # from the time.
-
-        tried_domains = set(likely_domains)
-        tried_domains.add(self.server_name)
-
-        event_ids = list(extremities.keys())
-
-        logger.debug("calling resolve_state_groups in _maybe_backfill")
-        resolve = preserve_fn(self.state_handler.resolve_state_groups_for_events)
-        states_list = await make_deferred_yieldable(
-            defer.gatherResults(
-                [resolve(room_id, [e]) for e in event_ids], consumeErrors=True
-            )
-        )
-
-        # A map from event_id to state map of event_ids.
-        state_ids: Dict[str, StateMap[str]] = dict(
-            zip(event_ids, [s.state for s in states_list])
-        )
-
-        state_map = await self.store.get_events(
-            [e_id for ids in state_ids.values() for e_id in ids.values()],
-            get_prev_content=False,
-        )
-
-        # A map from event_id to state map of events.
-        state_events: Dict[str, StateMap[EventBase]] = {
-            key: {
-                k: state_map[e_id]
-                for k, e_id in state_dict.items()
-                if e_id in state_map
-            }
-            for key, state_dict in state_ids.items()
-        }
-
-        for e_id in event_ids:
-            likely_extremeties_domains = get_domains_from_state(state_events[e_id])
-
-            success = await try_backfill(
-                [
-                    dom
-                    for dom, _ in likely_extremeties_domains
-                    if dom not in tried_domains
-                ]
-            )
-            if success:
-                return True
-
-            tried_domains.update(dom for dom, _ in likely_extremeties_domains)
+        # TODO: we could also try servers which were previously in the room, but
+        #   are no longer.
 
         return False
 
diff --git a/synapse/handlers/initial_sync.py b/synapse/handlers/initial_sync.py
index 344f20f37cce..a7db8feb57eb 100644
--- a/synapse/handlers/initial_sync.py
+++ b/synapse/handlers/initial_sync.py
@@ -18,6 +18,7 @@
 from synapse.api.constants import EduTypes, EventTypes, Membership
 from synapse.api.errors import SynapseError
 from synapse.events import EventBase
+from synapse.events.utils import SerializeEventConfig
 from synapse.events.validator import EventValidator
 from synapse.handlers.presence import format_user_presence_state
 from synapse.handlers.receipts import ReceiptEventSource
@@ -152,10 +153,13 @@ async def _snapshot_all_rooms(
 
         public_room_ids = await self.store.get_public_room_ids()
 
-        limit = pagin_config.limit
-        if limit is None:
+        if pagin_config.limit is not None:
+            limit = pagin_config.limit
+        else:
             limit = 10
 
+        serializer_options = SerializeEventConfig(as_client_event=as_client_event)
+
         async def handle_room(event: RoomsForUser) -> None:
             d: JsonDict = {
                 "room_id": event.room_id,
@@ -173,7 +177,7 @@ async def handle_room(event: RoomsForUser) -> None:
                 d["invite"] = self._event_serializer.serialize_event(
                     invite_event,
                     time_now,
-                    as_client_event=as_client_event,
+                    config=serializer_options,
                 )
 
             rooms_ret.append(d)
@@ -225,7 +229,7 @@ async def handle_room(event: RoomsForUser) -> None:
                         self._event_serializer.serialize_events(
                             messages,
                             time_now=time_now,
-                            as_client_event=as_client_event,
+                            config=serializer_options,
                         )
                     ),
                     "start": await start_token.to_string(self.store),
@@ -235,7 +239,7 @@ async def handle_room(event: RoomsForUser) -> None:
                 d["state"] = self._event_serializer.serialize_events(
                     current_state.values(),
                     time_now=time_now,
-                    as_client_event=as_client_event,
+                    config=serializer_options,
                 )
 
                 account_data_events = []
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 68f3927a8e1a..9e812f3db219 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -1069,6 +1069,9 @@ async def _validate_event_relation(self, event: EventBase) -> None:
         if relation_type == RelationTypes.ANNOTATION:
             aggregation_key = relation["key"]
 
+            if len(aggregation_key) > 500:
+                raise SynapseError(400, "Aggregation key is too long")
+
             already_exists = await self.store.has_user_annotated_event(
                 relates_to, event.type, aggregation_key, event.sender
             )
@@ -1076,7 +1079,10 @@ async def _validate_event_relation(self, event: EventBase) -> None:
                 raise SynapseError(400, "Can't send same reaction twice")
 
         # Don't attempt to start a thread if the parent event is a relation.
-        elif relation_type == RelationTypes.THREAD:
+        elif (
+            relation_type == RelationTypes.THREAD
+            or relation_type == RelationTypes.UNSTABLE_THREAD
+        ):
             if await self.store.event_includes_relation(relates_to):
                 raise SynapseError(
                     400, "Cannot start threads from an event with a relation"
diff --git a/synapse/handlers/oidc.py b/synapse/handlers/oidc.py
index 593a2aac6691..724b9cfcb4bb 100644
--- a/synapse/handlers/oidc.py
+++ b/synapse/handlers/oidc.py
@@ -45,6 +45,7 @@
 from synapse.util import Clock, json_decoder
 from synapse.util.caches.cached_call import RetryOnExceptionCachedCall
 from synapse.util.macaroons import get_value_from_macaroon, satisfy_expiry
+from synapse.util.templates import _localpart_from_email_filter
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
@@ -1228,6 +1229,7 @@ class OidcSessionData:
 
 class UserAttributeDict(TypedDict):
     localpart: Optional[str]
+    confirm_localpart: bool
     display_name: Optional[str]
     emails: List[str]
 
@@ -1307,6 +1309,11 @@ def jinja_finalize(thing: Any) -> Any:
 
 
 env = Environment(finalize=jinja_finalize)
+env.filters.update(
+    {
+        "localpart_from_email": _localpart_from_email_filter,
+    }
+)
 
 
 @attr.s(slots=True, frozen=True, auto_attribs=True)
@@ -1316,6 +1323,7 @@ class JinjaOidcMappingConfig:
     display_name_template: Optional[Template]
     email_template: Optional[Template]
     extra_attributes: Dict[str, Template]
+    confirm_localpart: bool = False
 
 
 class JinjaOidcMappingProvider(OidcMappingProvider[JinjaOidcMappingConfig]):
@@ -1357,12 +1365,17 @@ def parse_template_config(option_name: str) -> Optional[Template]:
                         "invalid jinja template", path=["extra_attributes", key]
                     ) from e
 
+        confirm_localpart = config.get("confirm_localpart") or False
+        if not isinstance(confirm_localpart, bool):
+            raise ConfigError("must be a bool", path=["confirm_localpart"])
+
         return JinjaOidcMappingConfig(
             subject_claim=subject_claim,
             localpart_template=localpart_template,
             display_name_template=display_name_template,
             email_template=email_template,
             extra_attributes=extra_attributes,
+            confirm_localpart=confirm_localpart,
         )
 
     def get_remote_user_id(self, userinfo: UserInfo) -> str:
@@ -1398,7 +1411,10 @@ def render_template_field(template: Optional[Template]) -> Optional[str]:
             emails.append(email)
 
         return UserAttributeDict(
-            localpart=localpart, display_name=display_name, emails=emails
+            localpart=localpart,
+            display_name=display_name,
+            emails=emails,
+            confirm_localpart=self._config.confirm_localpart,
         )
 
     async def get_extra_attributes(self, userinfo: UserInfo, token: Token) -> JsonDict:
diff --git a/synapse/handlers/pagination.py b/synapse/handlers/pagination.py
index dba368764118..5cca7c53fbd6 100644
--- a/synapse/handlers/pagination.py
+++ b/synapse/handlers/pagination.py
@@ -24,6 +24,7 @@
 from synapse.api.constants import EventTypes, Membership
 from synapse.api.errors import SynapseError
 from synapse.api.filtering import Filter
+from synapse.events.utils import SerializeEventConfig
 from synapse.handlers.room import ShutdownRoomResponse
 from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.storage.state import StateFilter
@@ -353,7 +354,7 @@ async def _purge_history(
         """
         self._purges_in_progress_by_room.add(room_id)
         try:
-            with await self.pagination_lock.write(room_id):
+            async with self.pagination_lock.write(room_id):
                 await self.storage.purge_events.purge_history(
                     room_id, token, delete_local_events
                 )
@@ -411,7 +412,7 @@ async def purge_room(self, room_id: str, force: bool = False) -> None:
         """
         logger.info(f"[purge room] purging {room_id}, force={force}")
         purge_start = time.time()
-        with await self.pagination_lock.write(room_id):
+        async with self.pagination_lock.write(room_id):
             # first check that we have no users in this room
             if not force:
                 joined = await self.store.is_host_joined(room_id, self._server_name)
@@ -458,7 +459,7 @@ async def get_messages(
 
         room_token = from_token.room_key
 
-        with await self.pagination_lock.read(room_id):
+        async with self.pagination_lock.read(room_id):
             (
                 membership,
                 member_event_id,
@@ -552,13 +553,15 @@ async def get_messages(
 
         time_now = self.clock.time_msec()
 
+        serialize_options = SerializeEventConfig(as_client_event=as_client_event)
+
         chunk = {
             "chunk": (
                 self._event_serializer.serialize_events(
                     events,
                     time_now,
+                    config=serialize_options,
                     bundle_aggregations=aggregations,
-                    as_client_event=as_client_event,
                 )
             ),
             "start": await from_token.to_string(self.store),
@@ -567,7 +570,7 @@ async def get_messages(
 
         if state:
             chunk["state"] = self._event_serializer.serialize_events(
-                state, time_now, as_client_event=as_client_event
+                state, time_now, config=serialize_options
             )
 
         return chunk
@@ -623,7 +626,7 @@ async def _shutdown_and_purge_room(
 
         self._purges_in_progress_by_room.add(room_id)
         try:
-            with await self.pagination_lock.write(room_id):
+            async with self.pagination_lock.write(room_id):
                 self._delete_by_id[delete_id].status = DeleteStatus.STATUS_SHUTTING_DOWN
                 self._delete_by_id[
                     delete_id
diff --git a/synapse/handlers/presence.py b/synapse/handlers/presence.py
index c155098beeb8..34d9411bbf61 100644
--- a/synapse/handlers/presence.py
+++ b/synapse/handlers/presence.py
@@ -267,7 +267,6 @@ async def update_external_syncs_row(
             is_syncing: Whether or not the user is now syncing
             sync_time_msec: Time in ms when the user was last syncing
         """
-        pass
 
     async def update_external_syncs_clear(self, process_id: str) -> None:
         """Marks all users that had been marked as syncing by a given process
@@ -277,7 +276,6 @@ async def update_external_syncs_clear(self, process_id: str) -> None:
 
         This is a no-op when presence is handled by a different worker.
         """
-        pass
 
     async def process_replication_rows(
         self, stream_name: str, instance_name: str, token: int, rows: list
@@ -424,13 +422,13 @@ def __init__(self, hs: "HomeServer"):
 
     async def _on_shutdown(self) -> None:
         if self._presence_enabled:
-            self.hs.get_tcp_replication().send_command(
+            self.hs.get_replication_command_handler().send_command(
                 ClearUserSyncsCommand(self.instance_id)
             )
 
     def send_user_sync(self, user_id: str, is_syncing: bool, last_sync_ms: int) -> None:
         if self._presence_enabled:
-            self.hs.get_tcp_replication().send_user_sync(
+            self.hs.get_replication_command_handler().send_user_sync(
                 self.instance_id, user_id, is_syncing, last_sync_ms
             )
 
diff --git a/synapse/handlers/receipts.py b/synapse/handlers/receipts.py
index 5a7d0fdb70dc..d1a2fd2b1d4d 100644
--- a/synapse/handlers/receipts.py
+++ b/synapse/handlers/receipts.py
@@ -270,7 +270,7 @@ async def get_new_events_as(
         # Then filter down to rooms that the AS can read
         events = []
         for room_id, event in rooms_to_events.items():
-            if not await service.matches_user_in_member_list(room_id, self.store):
+            if not await service.is_interested_in_room(room_id, self.store):
                 continue
 
             events.append(event)
diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index 7b1224a3609e..8d51ffa033ed 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -1490,6 +1490,7 @@ def __init__(self, hs: "HomeServer"):
         self.room_member_handler = hs.get_room_member_handler()
         self._room_creation_handler = hs.get_room_creation_handler()
         self._replication = hs.get_replication_data_handler()
+        self._third_party_rules = hs.get_third_party_event_rules()
         self.event_creation_handler = hs.get_event_creation_handler()
         self.store = hs.get_datastores().main
 
@@ -1563,6 +1564,13 @@ async def shutdown_room(
         if not RoomID.is_valid(room_id):
             raise SynapseError(400, "%s is not a legal room ID" % (room_id,))
 
+        if not await self._third_party_rules.check_can_shutdown_room(
+            requester_user_id, room_id
+        ):
+            raise SynapseError(
+                403, "Shutdown of this room is forbidden", Codes.FORBIDDEN
+            )
+
         # Action the block first (even if the room doesn't exist yet)
         if block:
             # This will work even if the room is already blocked, but that is
diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index a582837cf0aa..7cbc484b0654 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -1736,8 +1736,8 @@ async def _generate_local_out_of_band_leave(
             txn_id=txn_id,
             prev_event_ids=prev_event_ids,
             auth_event_ids=auth_event_ids,
+            outlier=True,
         )
-        event.internal_metadata.outlier = True
         event.internal_metadata.out_of_band_membership = True
 
         result_event = await self.event_creation_handler.handle_new_client_event(
diff --git a/synapse/handlers/room_summary.py b/synapse/handlers/room_summary.py
index 55c2cbdba8bc..486145f48aca 100644
--- a/synapse/handlers/room_summary.py
+++ b/synapse/handlers/room_summary.py
@@ -295,7 +295,7 @@ async def _get_room_hierarchy(
             # inaccessible to the requesting user.
             if room_entry:
                 # Add the room (including the stripped m.space.child events).
-                rooms_result.append(room_entry.as_json())
+                rooms_result.append(room_entry.as_json(for_client=True))
 
                 # If this room is not at the max-depth, check if there are any
                 # children to process.
@@ -843,21 +843,32 @@ class _RoomEntry:
     # This may not include all children.
     children_state_events: Sequence[JsonDict] = ()
 
-    def as_json(self) -> JsonDict:
+    def as_json(self, for_client: bool = False) -> JsonDict:
         """
         Returns a JSON dictionary suitable for the room hierarchy endpoint.
 
         It returns the room summary including the stripped m.space.child events
         as a sub-key.
+
+        Args:
+            for_client: If true, any server-server only fields are stripped from
+                the result.
+
         """
         result = dict(self.room)
+
+        # Before returning to the client, remove the allowed_room_ids key, if it
+        # exists.
+        if for_client:
+            result.pop("allowed_room_ids", False)
+
         result["children_state"] = self.children_state_events
         return result
 
 
 def _has_valid_via(e: EventBase) -> bool:
     via = e.content.get("via")
-    if not via or not isinstance(via, Sequence):
+    if not via or not isinstance(via, list):
         return False
     for v in via:
         if not isinstance(v, str):
diff --git a/synapse/handlers/sso.py b/synapse/handlers/sso.py
index ff5b5169cac1..4f02a060d953 100644
--- a/synapse/handlers/sso.py
+++ b/synapse/handlers/sso.py
@@ -132,6 +132,7 @@ class UserAttributes:
     # if `None`, the mapper has not picked a userid, and the user should be prompted to
     # enter one.
     localpart: Optional[str]
+    confirm_localpart: bool = False
     display_name: Optional[str] = None
     emails: Collection[str] = attr.Factory(list)
 
@@ -561,9 +562,10 @@ def _get_url_for_next_new_user_step(
         # Must provide either attributes or session, not both
         assert (attributes is not None) != (session is not None)
 
-        if (attributes and attributes.localpart is None) or (
-            session and session.chosen_localpart is None
-        ):
+        if (
+            attributes
+            and (attributes.localpart is None or attributes.confirm_localpart is True)
+        ) or (session and session.chosen_localpart is None):
             return b"/_synapse/client/pick_username/account_details"
         elif self._consent_at_registration and not (
             session and session.terms_accepted_version
diff --git a/synapse/handlers/typing.py b/synapse/handlers/typing.py
index 843c68eb0fdf..6854428b7ca5 100644
--- a/synapse/handlers/typing.py
+++ b/synapse/handlers/typing.py
@@ -160,8 +160,9 @@ def process_replication_rows(
         """Should be called whenever we receive updates for typing stream."""
 
         if self._latest_room_serial > token:
-            # The master has gone backwards. To prevent inconsistent data, just
-            # clear everything.
+            # The typing worker has gone backwards (e.g. it may have restarted).
+            # To prevent inconsistent data, just clear everything.
+            logger.info("Typing handler stream went backwards; resetting")
             self._reset()
 
         # Set the latest serial token to whatever the server gave us.
@@ -486,9 +487,7 @@ async def get_new_events_as(
                 if handler._room_serials[room_id] <= from_key:
                     continue
 
-                if not await service.matches_user_in_member_list(
-                    room_id, self._main_store
-                ):
+                if not await service.is_interested_in_room(room_id, self._main_store):
                     continue
 
                 events.append(self._make_event_for(room_id))
diff --git a/synapse/http/matrixfederationclient.py b/synapse/http/matrixfederationclient.py
index 40bf1e06d602..6b98d865f5bb 100644
--- a/synapse/http/matrixfederationclient.py
+++ b/synapse/http/matrixfederationclient.py
@@ -120,7 +120,6 @@ def finish(self) -> T:
         """Called when response has finished streaming and the parser should
         return the final result (or error).
         """
-        pass
 
 
 @attr.s(slots=True, frozen=True, auto_attribs=True)
@@ -601,7 +600,6 @@ async def _send_request(
                             response.code,
                             response_phrase,
                         )
-                        pass
                     else:
                         logger.info(
                             "{%s} [%s] Got response headers: %d %s",
diff --git a/synapse/http/server.py b/synapse/http/server.py
index 09b412548968..31ca84188975 100644
--- a/synapse/http/server.py
+++ b/synapse/http/server.py
@@ -233,7 +233,6 @@ def register_paths(
             servlet_classname (str): The name of the handler to be used in prometheus
                 and opentracing logs.
         """
-        pass
 
 
 class _AsyncResource(resource.Resource, metaclass=abc.ABCMeta):
diff --git a/synapse/logging/context.py b/synapse/logging/context.py
index c31c2960ad95..88cd8a9e1c39 100644
--- a/synapse/logging/context.py
+++ b/synapse/logging/context.py
@@ -29,7 +29,6 @@
 from types import TracebackType
 from typing import (
     TYPE_CHECKING,
-    Any,
     Awaitable,
     Callable,
     Optional,
@@ -41,7 +40,7 @@
 )
 
 import attr
-from typing_extensions import Literal
+from typing_extensions import Literal, ParamSpec
 
 from twisted.internet import defer, threads
 from twisted.python.threadpool import ThreadPool
@@ -719,32 +718,33 @@ def nested_logging_context(suffix: str) -> LoggingContext:
     )
 
 
+P = ParamSpec("P")
 R = TypeVar("R")
 
 
 @overload
 def preserve_fn(  # type: ignore[misc]
-    f: Callable[..., Awaitable[R]],
-) -> Callable[..., "defer.Deferred[R]"]:
+    f: Callable[P, Awaitable[R]],
+) -> Callable[P, "defer.Deferred[R]"]:
     # The `type: ignore[misc]` above suppresses
     # "Overloaded function signatures 1 and 2 overlap with incompatible return types"
     ...
 
 
 @overload
-def preserve_fn(f: Callable[..., R]) -> Callable[..., "defer.Deferred[R]"]:
+def preserve_fn(f: Callable[P, R]) -> Callable[P, "defer.Deferred[R]"]:
     ...
 
 
 def preserve_fn(
     f: Union[
-        Callable[..., R],
-        Callable[..., Awaitable[R]],
+        Callable[P, R],
+        Callable[P, Awaitable[R]],
     ]
-) -> Callable[..., "defer.Deferred[R]"]:
+) -> Callable[P, "defer.Deferred[R]"]:
     """Function decorator which wraps the function with run_in_background"""
 
-    def g(*args: Any, **kwargs: Any) -> "defer.Deferred[R]":
+    def g(*args: P.args, **kwargs: P.kwargs) -> "defer.Deferred[R]":
         return run_in_background(f, *args, **kwargs)
 
     return g
@@ -752,7 +752,7 @@ def g(*args: Any, **kwargs: Any) -> "defer.Deferred[R]":
 
 @overload
 def run_in_background(  # type: ignore[misc]
-    f: Callable[..., Awaitable[R]], *args: Any, **kwargs: Any
+    f: Callable[P, Awaitable[R]], *args: P.args, **kwargs: P.kwargs
 ) -> "defer.Deferred[R]":
     # The `type: ignore[misc]` above suppresses
     # "Overloaded function signatures 1 and 2 overlap with incompatible return types"
@@ -761,18 +761,22 @@ def run_in_background(  # type: ignore[misc]
 
 @overload
 def run_in_background(
-    f: Callable[..., R], *args: Any, **kwargs: Any
+    f: Callable[P, R], *args: P.args, **kwargs: P.kwargs
 ) -> "defer.Deferred[R]":
     ...
 
 
-def run_in_background(
+def run_in_background(  # type: ignore[misc]
+    # The `type: ignore[misc]` above suppresses
+    # "Overloaded function implementation does not accept all possible arguments of signature 1"
+    # "Overloaded function implementation does not accept all possible arguments of signature 2"
+    # which seems like a bug in mypy.
     f: Union[
-        Callable[..., R],
-        Callable[..., Awaitable[R]],
+        Callable[P, R],
+        Callable[P, Awaitable[R]],
     ],
-    *args: Any,
-    **kwargs: Any,
+    *args: P.args,
+    **kwargs: P.kwargs,
 ) -> "defer.Deferred[R]":
     """Calls a function, ensuring that the current context is restored after
     return from the function, and that the sentinel context is set once the
@@ -872,7 +876,7 @@ def _set_context_cb(result: ResultT, context: LoggingContext) -> ResultT:
 
 
 def defer_to_thread(
-    reactor: "ISynapseReactor", f: Callable[..., R], *args: Any, **kwargs: Any
+    reactor: "ISynapseReactor", f: Callable[P, R], *args: P.args, **kwargs: P.kwargs
 ) -> "defer.Deferred[R]":
     """
     Calls the function `f` using a thread from the reactor's default threadpool and
@@ -908,9 +912,9 @@ def defer_to_thread(
 def defer_to_threadpool(
     reactor: "ISynapseReactor",
     threadpool: ThreadPool,
-    f: Callable[..., R],
-    *args: Any,
-    **kwargs: Any,
+    f: Callable[P, R],
+    *args: P.args,
+    **kwargs: P.kwargs,
 ) -> "defer.Deferred[R]":
     """
     A wrapper for twisted.internet.threads.deferToThreadpool, which handles
diff --git a/synapse/module_api/__init__.py b/synapse/module_api/__init__.py
index c42eeedd87ae..d735c1d4616e 100644
--- a/synapse/module_api/__init__.py
+++ b/synapse/module_api/__init__.py
@@ -54,6 +54,8 @@
     USER_MAY_SEND_3PID_INVITE_CALLBACK,
 )
 from synapse.events.third_party_rules import (
+    CHECK_CAN_DEACTIVATE_USER_CALLBACK,
+    CHECK_CAN_SHUTDOWN_ROOM_CALLBACK,
     CHECK_EVENT_ALLOWED_CALLBACK,
     CHECK_THREEPID_CAN_BE_INVITED_CALLBACK,
     CHECK_VISIBILITY_CAN_BE_MODIFIED_CALLBACK,
@@ -283,6 +285,8 @@ def register_third_party_rules_callbacks(
             CHECK_VISIBILITY_CAN_BE_MODIFIED_CALLBACK
         ] = None,
         on_new_event: Optional[ON_NEW_EVENT_CALLBACK] = None,
+        check_can_shutdown_room: Optional[CHECK_CAN_SHUTDOWN_ROOM_CALLBACK] = None,
+        check_can_deactivate_user: Optional[CHECK_CAN_DEACTIVATE_USER_CALLBACK] = None,
         on_profile_update: Optional[ON_PROFILE_UPDATE_CALLBACK] = None,
         on_user_deactivation_status_changed: Optional[
             ON_USER_DEACTIVATION_STATUS_CHANGED_CALLBACK
@@ -298,6 +302,8 @@ def register_third_party_rules_callbacks(
             check_threepid_can_be_invited=check_threepid_can_be_invited,
             check_visibility_can_be_modified=check_visibility_can_be_modified,
             on_new_event=on_new_event,
+            check_can_shutdown_room=check_can_shutdown_room,
+            check_can_deactivate_user=check_can_deactivate_user,
             on_profile_update=on_profile_update,
             on_user_deactivation_status_changed=on_user_deactivation_status_changed,
         )
diff --git a/synapse/push/baserules.py b/synapse/push/baserules.py
index 10bc08271b13..78267812d8df 100644
--- a/synapse/push/baserules.py
+++ b/synapse/push/baserules.py
@@ -172,13 +172,13 @@ def make_base_prepend_rules(
                 "kind": "event_match",
                 "key": "type",
                 "pattern": "m.room.member",
-                "_id": "_member",
+                "_cache_key": "_member",
             },
             {  # with membership = invite
                 "kind": "event_match",
                 "key": "content.membership",
                 "pattern": "invite",
-                "_id": "_invite_member",
+                "_cache_key": "_invite_member",
             },
             {  # matching the current user ID
                 "kind": "event_match",
@@ -189,7 +189,7 @@ def make_base_prepend_rules(
                 "kind": "event_match",
                 "key": "content.fi.mau.will_auto_accept",
                 "pattern": "true",
-                "_id": "_will_auto_accept",
+                "_cache_key": "_will_auto_accept",
             },
         ],
         "actions": ["dont_notify"],
@@ -203,13 +203,13 @@ def make_base_prepend_rules(
                 "kind": "event_match",
                 "key": "type",
                 "pattern": "m.room.member",
-                "_id": "_member",
+                "_cache_key": "_member",
             },
             {
                 "kind": "event_match",
                 "key": "content.membership",
                 "pattern": "invite",
-                "_id": "_invite_member",
+                "_cache_key": "_invite_member",
             },
             {"kind": "event_match", "key": "state_key", "pattern_type": "user_id"},
         ],
@@ -232,7 +232,7 @@ def make_base_prepend_rules(
                 "kind": "event_match",
                 "key": "type",
                 "pattern": "m.room.member",
-                "_id": "_member",
+                "_cache_key": "_member",
             }
         ],
         "actions": ["dont_notify"],
@@ -257,12 +257,12 @@ def make_base_prepend_rules(
                 "kind": "event_match",
                 "key": "content.body",
                 "pattern": "@room",
-                "_id": "_roomnotif_content",
+                "_cache_key": "_roomnotif_content",
             },
             {
                 "kind": "sender_notification_permission",
                 "key": "room",
-                "_id": "_roomnotif_pl",
+                "_cache_key": "_roomnotif_pl",
             },
         ],
         "actions": ["notify", {"set_tweak": "highlight", "value": True}],
@@ -274,13 +274,13 @@ def make_base_prepend_rules(
                 "kind": "event_match",
                 "key": "type",
                 "pattern": "m.room.tombstone",
-                "_id": "_tombstone",
+                "_cache_key": "_tombstone",
             },
             {
                 "kind": "event_match",
                 "key": "state_key",
                 "pattern": "",
-                "_id": "_tombstone_statekey",
+                "_cache_key": "_tombstone_statekey",
             },
         ],
         "actions": ["notify", {"set_tweak": "highlight", "value": True}],
@@ -299,7 +299,7 @@ def make_base_prepend_rules(
                 "kind": "event_match",
                 "key": "content.msgtype",
                 "pattern": "m.notice",
-                "_id": "_suppress_notices",
+                "_cache_key": "_suppress_notices",
             }
         ],
         "actions": ["dont_notify"],
@@ -311,7 +311,7 @@ def make_base_prepend_rules(
                 "kind": "event_match",
                 "key": "type",
                 "pattern": "m.call.invite",
-                "_id": "_call",
+                "_cache_key": "_call",
             }
         ],
         "actions": [
@@ -325,12 +325,12 @@ def make_base_prepend_rules(
     {
         "rule_id": "global/underride/.m.rule.room_one_to_one",
         "conditions": [
-            {"kind": "room_member_count", "is": "2", "_id": "member_count"},
+            {"kind": "room_member_count", "is": "2", "_cache_key": "member_count"},
             {
                 "kind": "event_match",
                 "key": "type",
                 "pattern": "m.room.message",
-                "_id": "_message",
+                "_cache_key": "_message",
             },
         ],
         "actions": [
@@ -344,12 +344,12 @@ def make_base_prepend_rules(
     {
         "rule_id": "global/underride/.m.rule.encrypted_room_one_to_one",
         "conditions": [
-            {"kind": "room_member_count", "is": "2", "_id": "member_count"},
+            {"kind": "room_member_count", "is": "2", "_cache_key": "member_count"},
             {
                 "kind": "event_match",
                 "key": "type",
                 "pattern": "m.room.encrypted",
-                "_id": "_encrypted",
+                "_cache_key": "_encrypted",
             },
         ],
         "actions": [
@@ -365,7 +365,7 @@ def make_base_prepend_rules(
                 "kind": "event_match",
                 "key": "type",
                 "pattern": "m.room.message",
-                "_id": "_message",
+                "_cache_key": "_message",
             }
         ],
         "actions": ["notify", {"set_tweak": "highlight", "value": False}],
@@ -379,7 +379,7 @@ def make_base_prepend_rules(
                 "kind": "event_match",
                 "key": "type",
                 "pattern": "m.room.encrypted",
-                "_id": "_encrypted",
+                "_cache_key": "_encrypted",
             }
         ],
         "actions": ["notify", {"set_tweak": "highlight", "value": False}],
@@ -391,19 +391,19 @@ def make_base_prepend_rules(
                 "kind": "event_match",
                 "key": "type",
                 "pattern": "im.vector.modular.widgets",
-                "_id": "_type_modular_widgets",
+                "_cache_key": "_type_modular_widgets",
             },
             {
                 "kind": "event_match",
                 "key": "content.type",
                 "pattern": "jitsi",
-                "_id": "_content_type_jitsi",
+                "_cache_key": "_content_type_jitsi",
             },
             {
                 "kind": "event_match",
                 "key": "state_key",
                 "pattern": "*",
-                "_id": "_is_state_event",
+                "_cache_key": "_is_state_event",
             },
         ],
         "actions": ["notify", {"set_tweak": "highlight", "value": False}],
@@ -416,13 +416,13 @@ def make_base_prepend_rules(
                 "kind": "event_match",
                 "key": "type",
                 "pattern": "m.reaction",
-                "_id": "_reaction",
+                "_cache_key": "_reaction",
             },
             # Only send reaction notifications for smaller rooms (under 20 members)
             {
                 "kind": "room_member_count",
                 "is": "<20",
-                "_id": "_member_count",
+                "_cache_key": "_member_count",
             },
             # Only send notification if the reaction is to your message
             {
diff --git a/synapse/push/bulk_push_rule_evaluator.py b/synapse/push/bulk_push_rule_evaluator.py
index 726474205438..bfa10c9713e7 100644
--- a/synapse/push/bulk_push_rule_evaluator.py
+++ b/synapse/push/bulk_push_rule_evaluator.py
@@ -279,17 +279,17 @@ def _condition_checker(
     cache: Dict[str, bool],
 ) -> bool:
     for cond in conditions:
-        _id = cond.get("_id", None)
-        if _id:
-            res = cache.get(_id, None)
+        _cache_key = cond.get("_cache_key", None)
+        if _cache_key:
+            res = cache.get(_cache_key, None)
             if res is False:
                 return False
             elif res is True:
                 continue
 
         res = evaluator.matches(cond, uid, display_name)
-        if _id:
-            cache[_id] = bool(res)
+        if _cache_key:
+            cache[_cache_key] = bool(res)
 
         if not res:
             return False
diff --git a/synapse/push/clientformat.py b/synapse/push/clientformat.py
index c5708cd8885b..63b22d50aea9 100644
--- a/synapse/push/clientformat.py
+++ b/synapse/push/clientformat.py
@@ -40,7 +40,7 @@ def format_push_rules_for_user(
 
         # Remove internal stuff.
         for c in r["conditions"]:
-            c.pop("_id", None)
+            c.pop("_cache_key", None)
 
             pattern_type = c.pop("pattern_type", None)
             if pattern_type == "user_id":
diff --git a/synapse/python_dependencies.py b/synapse/python_dependencies.py
index b40a7bbb76ca..1dd39f06cffb 100644
--- a/synapse/python_dependencies.py
+++ b/synapse/python_dependencies.py
@@ -76,7 +76,8 @@
     "netaddr>=0.7.18",
     "Jinja2>=2.9",
     "bleach>=1.4.3",
-    "typing-extensions>=3.7.4",
+    # We use `ParamSpec`, which was added in `typing-extensions` 3.10.0.0.
+    "typing-extensions>=3.10.0",
     # We enforce that we have a `cryptography` version that bundles an `openssl`
     # with the latest security patches.
     "cryptography>=3.4.7",
diff --git a/synapse/replication/slave/storage/client_ips.py b/synapse/replication/slave/storage/client_ips.py
index b5b84c09ae41..14706a081755 100644
--- a/synapse/replication/slave/storage/client_ips.py
+++ b/synapse/replication/slave/storage/client_ips.py
@@ -54,6 +54,6 @@ async def insert_client_ip(
 
         self.client_ip_last_seen.set(key, now)
 
-        self.hs.get_tcp_replication().send_user_ip(
+        self.hs.get_replication_command_handler().send_user_ip(
             user_id, access_token, ip, user_agent, device_id, now
         )
diff --git a/synapse/replication/tcp/client.py b/synapse/replication/tcp/client.py
index 1b8479b0b4ec..deeaaec4e66c 100644
--- a/synapse/replication/tcp/client.py
+++ b/synapse/replication/tcp/client.py
@@ -380,7 +380,7 @@ async def process_replication_rows(
             # changes.
             hosts = {row.entity for row in rows if not row.entity.startswith("@")}
             for host in hosts:
-                self.federation_sender.send_device_messages(host)
+                self.federation_sender.send_device_messages(host, immediate=False)
 
         elif stream_name == ToDeviceStream.NAME:
             # The to_device stream includes stuff to be pushed to both local
@@ -462,6 +462,8 @@ async def _save_and_send_ack(self) -> None:
 
                 # We ACK this token over replication so that the master can drop
                 # its in memory queues
-                self._hs.get_tcp_replication().send_federation_ack(current_position)
+                self._hs.get_replication_command_handler().send_federation_ack(
+                    current_position
+                )
         except Exception:
             logger.exception("Error updating federation stream position")
diff --git a/synapse/replication/tcp/external_cache.py b/synapse/replication/tcp/external_cache.py
index aaf91e5e0253..bf7d017968f9 100644
--- a/synapse/replication/tcp/external_cache.py
+++ b/synapse/replication/tcp/external_cache.py
@@ -21,7 +21,7 @@
 from synapse.util import json_decoder, json_encoder
 
 if TYPE_CHECKING:
-    from txredisapi import RedisProtocol
+    from txredisapi import ConnectionHandler
 
     from synapse.server import HomeServer
 
@@ -63,7 +63,7 @@ class ExternalCache:
     def __init__(self, hs: "HomeServer"):
         if hs.config.redis.redis_enabled:
             self._redis_connection: Optional[
-                "RedisProtocol"
+                "ConnectionHandler"
             ] = hs.get_outbound_redis_connection()
         else:
             self._redis_connection = None
diff --git a/synapse/replication/tcp/handler.py b/synapse/replication/tcp/handler.py
index 0d2013a3cfc5..b217c35f995d 100644
--- a/synapse/replication/tcp/handler.py
+++ b/synapse/replication/tcp/handler.py
@@ -295,9 +295,7 @@ async def _process_command(
             raise Exception("Unrecognised command %s in stream queue", cmd.NAME)
 
     def start_replication(self, hs: "HomeServer") -> None:
-        """Helper method to start a replication connection to the remote server
-        using TCP.
-        """
+        """Helper method to start replication."""
         if hs.config.redis.redis_enabled:
             from synapse.replication.tcp.redis import (
                 RedisDirectTcpReplicationClientFactory,
@@ -711,7 +709,7 @@ def send_remote_server_up(self, server: str) -> None:
         self.send_command(RemoteServerUpCommand(server))
 
     def stream_update(self, stream_name: str, token: Optional[int], data: Any) -> None:
-        """Called when a new update is available to stream to clients.
+        """Called when a new update is available to stream to Redis subscribers.
 
         We need to check if the client is interested in the stream or not
         """
diff --git a/synapse/replication/tcp/redis.py b/synapse/replication/tcp/redis.py
index 3170f7c59b04..989c5be0327e 100644
--- a/synapse/replication/tcp/redis.py
+++ b/synapse/replication/tcp/redis.py
@@ -93,7 +93,7 @@ class RedisSubscriber(txredisapi.SubscriberProtocol):
 
     synapse_handler: "ReplicationCommandHandler"
     synapse_stream_name: str
-    synapse_outbound_redis_connection: txredisapi.RedisProtocol
+    synapse_outbound_redis_connection: txredisapi.ConnectionHandler
 
     def __init__(self, *args: Any, **kwargs: Any):
         super().__init__(*args, **kwargs)
@@ -313,7 +313,7 @@ class RedisDirectTcpReplicationClientFactory(SynapseRedisFactory):
     protocol = RedisSubscriber
 
     def __init__(
-        self, hs: "HomeServer", outbound_redis_connection: txredisapi.RedisProtocol
+        self, hs: "HomeServer", outbound_redis_connection: txredisapi.ConnectionHandler
     ):
 
         super().__init__(
@@ -325,7 +325,7 @@ def __init__(
             password=hs.config.redis.redis_password,
         )
 
-        self.synapse_handler = hs.get_tcp_replication()
+        self.synapse_handler = hs.get_replication_command_handler()
         self.synapse_stream_name = hs.hostname
 
         self.synapse_outbound_redis_connection = outbound_redis_connection
@@ -353,7 +353,7 @@ def lazyConnection(
     reconnect: bool = True,
     password: Optional[str] = None,
     replyTimeout: int = 30,
-) -> txredisapi.RedisProtocol:
+) -> txredisapi.ConnectionHandler:
     """Creates a connection to Redis that is lazily set up and reconnects if the
     connections is lost.
     """
diff --git a/synapse/replication/tcp/resource.py b/synapse/replication/tcp/resource.py
index 494e42a2be8f..c6870df8f954 100644
--- a/synapse/replication/tcp/resource.py
+++ b/synapse/replication/tcp/resource.py
@@ -44,7 +44,7 @@ class ReplicationStreamProtocolFactory(ServerFactory):
     """Factory for new replication connections."""
 
     def __init__(self, hs: "HomeServer"):
-        self.command_handler = hs.get_tcp_replication()
+        self.command_handler = hs.get_replication_command_handler()
         self.clock = hs.get_clock()
         self.server_name = hs.config.server.server_name
 
@@ -67,8 +67,8 @@ def buildProtocol(self, addr: IAddress) -> ServerReplicationStreamProtocol:
 class ReplicationStreamer:
     """Handles replication connections.
 
-    This needs to be poked when new replication data may be available. When new
-    data is available it will propagate to all connected clients.
+    This needs to be poked when new replication data may be available.
+    When new data is available it will propagate to all Redis subscribers.
     """
 
     def __init__(self, hs: "HomeServer"):
@@ -85,7 +85,7 @@ def __init__(self, hs: "HomeServer"):
         self.is_looping = False
         self.pending_updates = False
 
-        self.command_handler = hs.get_tcp_replication()
+        self.command_handler = hs.get_replication_command_handler()
 
         # Set of streams to replicate.
         self.streams = self.command_handler.get_streams_to_replicate()
@@ -109,7 +109,7 @@ def __init__(self, hs: "HomeServer"):
 
     def on_notifier_poke(self) -> None:
         """Checks if there is actually any new data and sends it to the
-        connections if there are.
+        Redis subscribers if there are.
 
         This should get called each time new data is available, even if it
         is currently being executed, so that nothing gets missed
diff --git a/synapse/replication/tcp/streams/_base.py b/synapse/replication/tcp/streams/_base.py
index 23d631a76944..495f2f0285ba 100644
--- a/synapse/replication/tcp/streams/_base.py
+++ b/synapse/replication/tcp/streams/_base.py
@@ -316,7 +316,19 @@ def __init__(self, hs: "HomeServer"):
 class TypingStream(Stream):
     @attr.s(slots=True, frozen=True, auto_attribs=True)
     class TypingStreamRow:
+        """
+        An entry in the typing stream.
+        Describes all the users that are 'typing' right now in one room.
+
+        When a user stops typing, it will be streamed as a new update with that
+        user absent; you can think of the `user_ids` list as overwriting the
+        entire list that was there previously.
+        """
+
+        # The room that this update is for.
         room_id: str
+
+        # All the users that are 'typing' right now in the specified room.
         user_ids: List[str]
 
     NAME = "typing"
diff --git a/synapse/res/templates/sso_auth_account_details.html b/synapse/res/templates/sso_auth_account_details.html
index 00e1dcdbb866..1ba850369a32 100644
--- a/synapse/res/templates/sso_auth_account_details.html
+++ b/synapse/res/templates/sso_auth_account_details.html
@@ -130,22 +130,22 @@
   </head>
   <body>
     <header>
-      <h1>Your account is nearly ready</h1>
-      <p>Check your details before creating an account on {{ server_name }}</p>
+      <h1>Create your account</h1>
+      <p>This is required. Continue to create your account on {{ server_name }}. You can't change this later.</p>
     </header>
     <main>
       <form method="post" class="form__input" id="form">
         <div class="username_input" id="username_input">
-          <label for="field-username">Username</label>
+          <label for="field-username">Username (required)</label>
           <div class="prefix">@</div>
-          <input type="text" name="username" id="field-username" autofocus>
+          <input type="text" name="username" id="field-username" value="{{ user_attributes.localpart }}" autofocus>
           <div class="postfix">:{{ server_name }}</div>
         </div>
         <output for="username_input" id="field-username-output"></output>
         <input type="submit" value="Continue" class="primary-button">
         {% if user_attributes.avatar_url or user_attributes.display_name or user_attributes.emails %}
         <section class="idp-pick-details">
-          <h2>{% if idp.idp_icon %}<img src="{{ idp.idp_icon | mxc_to_http(24, 24) }}"/>{% endif %}Information from {{ idp.idp_name }}</h2>
+          <h2>{% if idp.idp_icon %}<img src="{{ idp.idp_icon | mxc_to_http(24, 24) }}"/>{% endif %}Optional data from {{ idp.idp_name }}</h2>
           {% if user_attributes.avatar_url %}
           <label class="idp-detail idp-avatar" for="idp-avatar">
             <div class="check-row">
diff --git a/synapse/res/templates/sso_auth_account_details.js b/synapse/res/templates/sso_auth_account_details.js
index 3c45df9078f2..82438519a219 100644
--- a/synapse/res/templates/sso_auth_account_details.js
+++ b/synapse/res/templates/sso_auth_account_details.js
@@ -62,7 +62,7 @@ function validateUsername(username) {
     usernameField.parentElement.classList.remove("invalid");
     usernameOutput.classList.remove("error");
     if (!username) {
-        return reportError("Please provide a username");
+        return reportError("This is required. Please provide a username");
     }
     if (username.length > 255) {
         return reportError("Too long, please choose something shorter");
diff --git a/synapse/res/templates/sso_footer.html b/synapse/res/templates/sso_footer.html
index 588a3d508d6f..b46e0d83fe13 100644
--- a/synapse/res/templates/sso_footer.html
+++ b/synapse/res/templates/sso_footer.html
@@ -15,5 +15,5 @@
               </g>
           </g>
       </svg>
-      <p>An open network for secure, decentralized communication.<br>© 2021 The Matrix.org Foundation C.I.C.</p>
+      <p>An open network for secure, decentralized communication.<br>© 2022 The Matrix.org Foundation C.I.C.</p>
 </footer>
\ No newline at end of file
diff --git a/synapse/rest/__init__.py b/synapse/rest/__init__.py
index cebdeecb8127..762808a5717b 100644
--- a/synapse/rest/__init__.py
+++ b/synapse/rest/__init__.py
@@ -118,7 +118,8 @@ def register_servlets(client_resource: HttpServer, hs: "HomeServer") -> None:
         thirdparty.register_servlets(hs, client_resource)
         sendtodevice.register_servlets(hs, client_resource)
         user_directory.register_servlets(hs, client_resource)
-        groups.register_servlets(hs, client_resource)
+        if hs.config.experimental.groups_enabled:
+            groups.register_servlets(hs, client_resource)
         room_upgrade_rest_servlet.register_servlets(hs, client_resource)
         room_batch.register_servlets(hs, client_resource)
         capabilities.register_servlets(hs, client_resource)
diff --git a/synapse/rest/admin/__init__.py b/synapse/rest/admin/__init__.py
index 6de302f81352..cb4d55c89d78 100644
--- a/synapse/rest/admin/__init__.py
+++ b/synapse/rest/admin/__init__.py
@@ -293,7 +293,8 @@ def register_servlets_for_client_rest_resource(
     ResetPasswordRestServlet(hs).register(http_server)
     SearchUsersRestServlet(hs).register(http_server)
     UserRegisterServlet(hs).register(http_server)
-    DeleteGroupAdminRestServlet(hs).register(http_server)
+    if hs.config.experimental.groups_enabled:
+        DeleteGroupAdminRestServlet(hs).register(http_server)
     AccountValidityRenewServlet(hs).register(http_server)
 
     # Load the media repo ones if we're using them. Otherwise load the servlets which
diff --git a/synapse/rest/admin/rooms.py b/synapse/rest/admin/rooms.py
index 5b7053966662..4a17ea9e8452 100644
--- a/synapse/rest/admin/rooms.py
+++ b/synapse/rest/admin/rooms.py
@@ -75,6 +75,7 @@ def __init__(self, hs: "HomeServer"):
         self._auth = hs.get_auth()
         self._store = hs.get_datastores().main
         self._pagination_handler = hs.get_pagination_handler()
+        self._third_party_rules = hs.get_third_party_event_rules()
 
     async def on_DELETE(
         self, request: SynapseRequest, room_id: str
@@ -114,6 +115,14 @@ async def on_DELETE(
                 HTTPStatus.BAD_REQUEST, "%s is not a legal room ID" % (room_id,)
             )
 
+        # Check this here, as otherwise we'll only fail after the background job has been started.
+        if not await self._third_party_rules.check_can_shutdown_room(
+            requester.user.to_string(), room_id
+        ):
+            raise SynapseError(
+                403, "Shutdown of this room is forbidden", Codes.FORBIDDEN
+            )
+
         delete_id = self._pagination_handler.start_shutdown_and_purge_room(
             room_id=room_id,
             new_room_user_id=content.get("new_room_user_id"),
diff --git a/synapse/rest/client/notifications.py b/synapse/rest/client/notifications.py
index 20377a9ac628..ff040de6b840 100644
--- a/synapse/rest/client/notifications.py
+++ b/synapse/rest/client/notifications.py
@@ -16,7 +16,10 @@
 from typing import TYPE_CHECKING, Tuple
 
 from synapse.api.constants import ReceiptTypes
-from synapse.events.utils import format_event_for_client_v2_without_room_id
+from synapse.events.utils import (
+    SerializeEventConfig,
+    format_event_for_client_v2_without_room_id,
+)
 from synapse.http.server import HttpServer
 from synapse.http.servlet import RestServlet, parse_integer, parse_string
 from synapse.http.site import SynapseRequest
@@ -75,7 +78,9 @@ async def on_GET(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
                     self._event_serializer.serialize_event(
                         notif_events[pa.event_id],
                         self.clock.time_msec(),
-                        event_format=format_event_for_client_v2_without_room_id,
+                        config=SerializeEventConfig(
+                            event_format=format_event_for_client_v2_without_room_id
+                        ),
                     )
                 ),
             }
diff --git a/synapse/rest/client/relations.py b/synapse/rest/client/relations.py
index 487ea38b55cc..d9a6be43f793 100644
--- a/synapse/rest/client/relations.py
+++ b/synapse/rest/client/relations.py
@@ -27,50 +27,15 @@
 from synapse.http.servlet import RestServlet, parse_integer, parse_string
 from synapse.http.site import SynapseRequest
 from synapse.rest.client._base import client_patterns
-from synapse.storage.relations import (
-    AggregationPaginationToken,
-    PaginationChunk,
-    RelationPaginationToken,
-)
-from synapse.types import JsonDict, RoomStreamToken, StreamToken
+from synapse.storage.relations import AggregationPaginationToken
+from synapse.types import JsonDict, StreamToken
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
-    from synapse.storage.databases.main import DataStore
 
 logger = logging.getLogger(__name__)
 
 
-async def _parse_token(
-    store: "DataStore", token: Optional[str]
-) -> Optional[StreamToken]:
-    """
-    For backwards compatibility support RelationPaginationToken, but new pagination
-    tokens are generated as full StreamTokens, to be compatible with /sync and /messages.
-    """
-    if not token:
-        return None
-    # Luckily the format for StreamToken and RelationPaginationToken differ enough
-    # that they can easily be separated. An "_" appears in the serialization of
-    # RoomStreamToken (as part of StreamToken), but RelationPaginationToken uses
-    # "-" only for separators.
-    if "_" in token:
-        return await StreamToken.from_string(store, token)
-    else:
-        relation_token = RelationPaginationToken.from_string(token)
-        return StreamToken(
-            room_key=RoomStreamToken(relation_token.topological, relation_token.stream),
-            presence_key=0,
-            typing_key=0,
-            receipt_key=0,
-            account_data_key=0,
-            push_rules_key=0,
-            to_device_key=0,
-            device_list_key=0,
-            groups_key=0,
-        )
-
-
 class RelationPaginationServlet(RestServlet):
     """API to paginate relations on an event by topological ordering, optionally
     filtered by relation type and event type.
@@ -117,24 +82,25 @@ async def on_GET(
         from_token_str = parse_string(request, "from")
         to_token_str = parse_string(request, "to")
 
-        if event.internal_metadata.is_redacted():
-            # If the event is redacted, return an empty list of relations
-            pagination_chunk = PaginationChunk(chunk=[])
-        else:
-            # Return the relations
-            from_token = await _parse_token(self.store, from_token_str)
-            to_token = await _parse_token(self.store, to_token_str)
-
-            pagination_chunk = await self.store.get_relations_for_event(
-                event_id=parent_id,
-                room_id=room_id,
-                relation_type=relation_type,
-                event_type=event_type,
-                limit=limit,
-                direction=direction,
-                from_token=from_token,
-                to_token=to_token,
-            )
+        # Return the relations
+        from_token = None
+        if from_token_str:
+            from_token = await StreamToken.from_string(self.store, from_token_str)
+        to_token = None
+        if to_token_str:
+            to_token = await StreamToken.from_string(self.store, to_token_str)
+
+        pagination_chunk = await self.store.get_relations_for_event(
+            event_id=parent_id,
+            event=event,
+            room_id=room_id,
+            relation_type=relation_type,
+            event_type=event_type,
+            limit=limit,
+            direction=direction,
+            from_token=from_token,
+            to_token=to_token,
+        )
 
         events = await self.store.get_events_as_list(
             [c["event_id"] for c in pagination_chunk.chunk]
@@ -224,27 +190,23 @@ async def on_GET(
         from_token_str = parse_string(request, "from")
         to_token_str = parse_string(request, "to")
 
-        if event.internal_metadata.is_redacted():
-            # If the event is redacted, return an empty list of relations
-            pagination_chunk = PaginationChunk(chunk=[])
-        else:
-            # Return the relations
-            from_token = None
-            if from_token_str:
-                from_token = AggregationPaginationToken.from_string(from_token_str)
-
-            to_token = None
-            if to_token_str:
-                to_token = AggregationPaginationToken.from_string(to_token_str)
-
-            pagination_chunk = await self.store.get_aggregation_groups_for_event(
-                event_id=parent_id,
-                room_id=room_id,
-                event_type=event_type,
-                limit=limit,
-                from_token=from_token,
-                to_token=to_token,
-            )
+        # Return the relations
+        from_token = None
+        if from_token_str:
+            from_token = AggregationPaginationToken.from_string(from_token_str)
+
+        to_token = None
+        if to_token_str:
+            to_token = AggregationPaginationToken.from_string(to_token_str)
+
+        pagination_chunk = await self.store.get_aggregation_groups_for_event(
+            event_id=parent_id,
+            room_id=room_id,
+            event_type=event_type,
+            limit=limit,
+            from_token=from_token,
+            to_token=to_token,
+        )
 
         return 200, await pagination_chunk.to_dict(self.store)
 
@@ -317,11 +279,16 @@ async def on_GET(
         from_token_str = parse_string(request, "from")
         to_token_str = parse_string(request, "to")
 
-        from_token = await _parse_token(self.store, from_token_str)
-        to_token = await _parse_token(self.store, to_token_str)
+        from_token = None
+        if from_token_str:
+            from_token = await StreamToken.from_string(self.store, from_token_str)
+        to_token = None
+        if to_token_str:
+            to_token = await StreamToken.from_string(self.store, to_token_str)
 
         result = await self.store.get_relations_for_event(
             event_id=parent_id,
+            event=event,
             room_id=room_id,
             relation_type=relation_type,
             event_type=event_type,
diff --git a/synapse/rest/client/sync.py b/synapse/rest/client/sync.py
index f3018ff69077..53c385a86cc1 100644
--- a/synapse/rest/client/sync.py
+++ b/synapse/rest/client/sync.py
@@ -14,24 +14,14 @@
 import itertools
 import logging
 from collections import defaultdict
-from typing import (
-    TYPE_CHECKING,
-    Any,
-    Callable,
-    Dict,
-    Iterable,
-    List,
-    Optional,
-    Tuple,
-    Union,
-)
+from typing import TYPE_CHECKING, Any, Dict, List, Optional, Tuple, Union
 
 from synapse.api.constants import Membership, PresenceState
 from synapse.api.errors import Codes, StoreError, SynapseError
 from synapse.api.filtering import FilterCollection
 from synapse.api.presence import UserPresenceState
-from synapse.events import EventBase
 from synapse.events.utils import (
+    SerializeEventConfig,
     format_event_for_client_v2_without_room_id,
     format_event_raw,
 )
@@ -48,7 +38,6 @@
 from synapse.http.servlet import RestServlet, parse_boolean, parse_integer, parse_string
 from synapse.http.site import SynapseRequest
 from synapse.logging.opentracing import trace
-from synapse.storage.databases.main.relations import BundledAggregations
 from synapse.types import JsonDict, StreamToken
 from synapse.util import json_decoder
 
@@ -239,28 +228,31 @@ async def encode_response(
         else:
             raise Exception("Unknown event format %s" % (filter.event_format,))
 
+        serialize_options = SerializeEventConfig(
+            event_format=event_formatter,
+            token_id=access_token_id,
+            only_event_fields=filter.event_fields,
+        )
+        stripped_serialize_options = SerializeEventConfig(
+            event_format=event_formatter,
+            token_id=access_token_id,
+            include_stripped_room_state=True,
+        )
+
         joined = await self.encode_joined(
-            sync_result.joined,
-            time_now,
-            access_token_id,
-            filter.event_fields,
-            event_formatter,
+            sync_result.joined, time_now, serialize_options
         )
 
         invited = await self.encode_invited(
-            sync_result.invited, time_now, access_token_id, event_formatter
+            sync_result.invited, time_now, stripped_serialize_options
         )
 
         knocked = await self.encode_knocked(
-            sync_result.knocked, time_now, access_token_id, event_formatter
+            sync_result.knocked, time_now, stripped_serialize_options
         )
 
         archived = await self.encode_archived(
-            sync_result.archived,
-            time_now,
-            access_token_id,
-            filter.event_fields,
-            event_formatter,
+            sync_result.archived, time_now, serialize_options
         )
 
         logger.debug("building sync response dict")
@@ -339,9 +331,7 @@ async def encode_joined(
         self,
         rooms: List[JoinedSyncResult],
         time_now: int,
-        token_id: Optional[int],
-        event_fields: List[str],
-        event_formatter: Callable[[JsonDict], JsonDict],
+        serialize_options: SerializeEventConfig,
     ) -> JsonDict:
         """
         Encode the joined rooms in a sync result
@@ -349,24 +339,14 @@ async def encode_joined(
         Args:
             rooms: list of sync results for rooms this user is joined to
             time_now: current time - used as a baseline for age calculations
-            token_id: ID of the user's auth token - used for namespacing
-                of transaction IDs
-            event_fields: List of event fields to include. If empty,
-                all fields will be returned.
-            event_formatter: function to convert from federation format
-                to client format
+            serialize_options: Event serializer options
         Returns:
             The joined rooms list, in our response format
         """
         joined = {}
         for room in rooms:
             joined[room.room_id] = await self.encode_room(
-                room,
-                time_now,
-                token_id,
-                joined=True,
-                only_fields=event_fields,
-                event_formatter=event_formatter,
+                room, time_now, joined=True, serialize_options=serialize_options
             )
 
         return joined
@@ -376,8 +356,7 @@ async def encode_invited(
         self,
         rooms: List[InvitedSyncResult],
         time_now: int,
-        token_id: Optional[int],
-        event_formatter: Callable[[JsonDict], JsonDict],
+        serialize_options: SerializeEventConfig,
     ) -> JsonDict:
         """
         Encode the invited rooms in a sync result
@@ -385,10 +364,7 @@ async def encode_invited(
         Args:
             rooms: list of sync results for rooms this user is invited to
             time_now: current time - used as a baseline for age calculations
-            token_id: ID of the user's auth token - used for namespacing
-                of transaction IDs
-            event_formatter: function to convert from federation format
-                to client format
+            serialize_options: Event serializer options
 
         Returns:
             The invited rooms list, in our response format
@@ -396,11 +372,7 @@ async def encode_invited(
         invited = {}
         for room in rooms:
             invite = self._event_serializer.serialize_event(
-                room.invite,
-                time_now,
-                token_id=token_id,
-                event_format=event_formatter,
-                include_stripped_room_state=True,
+                room.invite, time_now, config=serialize_options
             )
             unsigned = dict(invite.get("unsigned", {}))
             invite["unsigned"] = unsigned
@@ -415,8 +387,7 @@ async def encode_knocked(
         self,
         rooms: List[KnockedSyncResult],
         time_now: int,
-        token_id: Optional[int],
-        event_formatter: Callable[[Dict], Dict],
+        serialize_options: SerializeEventConfig,
     ) -> Dict[str, Dict[str, Any]]:
         """
         Encode the rooms we've knocked on in a sync result.
@@ -424,8 +395,7 @@ async def encode_knocked(
         Args:
             rooms: list of sync results for rooms this user is knocking on
             time_now: current time - used as a baseline for age calculations
-            token_id: ID of the user's auth token - used for namespacing of transaction IDs
-            event_formatter: function to convert from federation format to client format
+            serialize_options: Event serializer options
 
         Returns:
             The list of rooms the user has knocked on, in our response format.
@@ -433,11 +403,7 @@ async def encode_knocked(
         knocked = {}
         for room in rooms:
             knock = self._event_serializer.serialize_event(
-                room.knock,
-                time_now,
-                token_id=token_id,
-                event_format=event_formatter,
-                include_stripped_room_state=True,
+                room.knock, time_now, config=serialize_options
             )
 
             # Extract the `unsigned` key from the knock event.
@@ -470,9 +436,7 @@ async def encode_archived(
         self,
         rooms: List[ArchivedSyncResult],
         time_now: int,
-        token_id: Optional[int],
-        event_fields: List[str],
-        event_formatter: Callable[[JsonDict], JsonDict],
+        serialize_options: SerializeEventConfig,
     ) -> JsonDict:
         """
         Encode the archived rooms in a sync result
@@ -480,23 +444,14 @@ async def encode_archived(
         Args:
             rooms: list of sync results for rooms this user is joined to
             time_now: current time - used as a baseline for age calculations
-            token_id: ID of the user's auth token - used for namespacing
-                of transaction IDs
-            event_fields: List of event fields to include. If empty,
-                all fields will be returned.
-            event_formatter: function to convert from federation format to client format
+            serialize_options: Event serializer options
         Returns:
             The archived rooms list, in our response format
         """
         joined = {}
         for room in rooms:
             joined[room.room_id] = await self.encode_room(
-                room,
-                time_now,
-                token_id,
-                joined=False,
-                only_fields=event_fields,
-                event_formatter=event_formatter,
+                room, time_now, joined=False, serialize_options=serialize_options
             )
 
         return joined
@@ -505,10 +460,8 @@ async def encode_room(
         self,
         room: Union[JoinedSyncResult, ArchivedSyncResult],
         time_now: int,
-        token_id: Optional[int],
         joined: bool,
-        only_fields: Optional[List[str]],
-        event_formatter: Callable[[JsonDict], JsonDict],
+        serialize_options: SerializeEventConfig,
     ) -> JsonDict:
         """
         Args:
@@ -524,20 +477,6 @@ async def encode_room(
         Returns:
             The room, encoded in our response format
         """
-
-        def serialize(
-            events: Iterable[EventBase],
-            aggregations: Optional[Dict[str, BundledAggregations]] = None,
-        ) -> List[JsonDict]:
-            return self._event_serializer.serialize_events(
-                events,
-                time_now=time_now,
-                bundle_aggregations=aggregations,
-                token_id=token_id,
-                event_format=event_formatter,
-                only_event_fields=only_fields,
-            )
-
         state_dict = room.state
         timeline_events = room.timeline.events
 
@@ -554,9 +493,14 @@ def serialize(
                     event.room_id,
                 )
 
-        serialized_state = serialize(state_events)
-        serialized_timeline = serialize(
-            timeline_events, room.timeline.bundled_aggregations
+        serialized_state = self._event_serializer.serialize_events(
+            state_events, time_now, config=serialize_options
+        )
+        serialized_timeline = self._event_serializer.serialize_events(
+            timeline_events,
+            time_now,
+            config=serialize_options,
+            bundle_aggregations=room.timeline.bundled_aggregations,
         )
 
         account_data = room.account_data
diff --git a/synapse/rest/client/versions.py b/synapse/rest/client/versions.py
index 2e5d0e4e2258..9a65aa484360 100644
--- a/synapse/rest/client/versions.py
+++ b/synapse/rest/client/versions.py
@@ -101,6 +101,7 @@ def on_GET(self, request: Request) -> Tuple[int, JsonDict]:
                     "org.matrix.msc3030": self.config.experimental.msc3030_enabled,
                     # Adds support for thread relations, per MSC3440.
                     "org.matrix.msc3440": self.config.experimental.msc3440_enabled,
+                    "org.matrix.msc3440.stable": True,  # TODO: remove when "v1.3" is added above
                 },
             },
         )
diff --git a/synapse/rest/media/v1/_base.py b/synapse/rest/media/v1/_base.py
index 9b40fd8a6c23..c35d42fab89d 100644
--- a/synapse/rest/media/v1/_base.py
+++ b/synapse/rest/media/v1/_base.py
@@ -298,7 +298,6 @@ def write_to_consumer(self, consumer: IConsumer) -> Awaitable:
         Returns:
             Resolves once the response has finished being written
         """
-        pass
 
     def __enter__(self) -> None:
         pass
diff --git a/synapse/rest/media/v1/storage_provider.py b/synapse/rest/media/v1/storage_provider.py
index 18bf977d3d9f..1c9b71d69c77 100644
--- a/synapse/rest/media/v1/storage_provider.py
+++ b/synapse/rest/media/v1/storage_provider.py
@@ -16,7 +16,7 @@
 import logging
 import os
 import shutil
-from typing import TYPE_CHECKING, Optional
+from typing import TYPE_CHECKING, Callable, Optional
 
 from synapse.config._base import Config
 from synapse.logging.context import defer_to_thread, run_in_background
@@ -150,8 +150,13 @@ async def store_file(self, path: str, file_info: FileInfo) -> None:
         dirname = os.path.dirname(backup_fname)
         os.makedirs(dirname, exist_ok=True)
 
+        # mypy needs help inferring the type of the second parameter, which is generic
+        shutil_copyfile: Callable[[str, str], str] = shutil.copyfile
         await defer_to_thread(
-            self.hs.get_reactor(), shutil.copyfile, primary_fname, backup_fname
+            self.hs.get_reactor(),
+            shutil_copyfile,
+            primary_fname,
+            backup_fname,
         )
 
     async def fetch(self, path: str, file_info: FileInfo) -> Optional[Responder]:
diff --git a/synapse/rest/synapse/client/pick_username.py b/synapse/rest/synapse/client/pick_username.py
index 28ae08349705..6338fbaaa96d 100644
--- a/synapse/rest/synapse/client/pick_username.py
+++ b/synapse/rest/synapse/client/pick_username.py
@@ -92,12 +92,20 @@ async def _async_render_GET(self, request: Request) -> None:
             self._sso_handler.render_error(request, "bad_session", e.msg, code=e.code)
             return
 
+        # The configuration might mandate going through this step to validate an
+        # automatically generated localpart, so session.chosen_localpart might already
+        # be set.
+        localpart = ""
+        if session.chosen_localpart is not None:
+            localpart = session.chosen_localpart
+
         idp_id = session.auth_provider_id
         template_params = {
             "idp": self._sso_handler.get_identity_providers()[idp_id],
             "user_attributes": {
                 "display_name": session.display_name,
                 "emails": session.emails,
+                "localpart": localpart,
             },
         }
 
diff --git a/synapse/server.py b/synapse/server.py
index b5e2a319bcef..2fcf18a7a69a 100644
--- a/synapse/server.py
+++ b/synapse/server.py
@@ -145,7 +145,7 @@
 logger = logging.getLogger(__name__)
 
 if TYPE_CHECKING:
-    from txredisapi import RedisProtocol
+    from txredisapi import ConnectionHandler
 
     from synapse.handlers.oidc import OidcHandler
     from synapse.handlers.saml import SamlHandler
@@ -328,7 +328,6 @@ def start_listening(self) -> None:
         Does nothing in this base class; overridden in derived classes to start the
         appropriate listeners.
         """
-        pass
 
     def setup_background_tasks(self) -> None:
         """
@@ -639,7 +638,7 @@ def get_read_marker_handler(self) -> ReadMarkerHandler:
         return ReadMarkerHandler(self)
 
     @cache_in_self
-    def get_tcp_replication(self) -> ReplicationCommandHandler:
+    def get_replication_command_handler(self) -> ReplicationCommandHandler:
         return ReplicationCommandHandler(self)
 
     @cache_in_self
@@ -754,7 +753,7 @@ def get_oidc_handler(self) -> "OidcHandler":
 
     @cache_in_self
     def get_event_client_serializer(self) -> EventClientSerializer:
-        return EventClientSerializer()
+        return EventClientSerializer(self)
 
     @cache_in_self
     def get_password_policy_handler(self) -> PasswordPolicyHandler:
@@ -807,7 +806,7 @@ def get_account_handler(self) -> AccountHandler:
         return AccountHandler(self)
 
     @cache_in_self
-    def get_outbound_redis_connection(self) -> "RedisProtocol":
+    def get_outbound_redis_connection(self) -> "ConnectionHandler":
         """
         The Redis connection used for replication.
 
diff --git a/synapse/state/__init__.py b/synapse/state/__init__.py
index 6babd5963cc1..21888cc8c561 100644
--- a/synapse/state/__init__.py
+++ b/synapse/state/__init__.py
@@ -194,7 +194,7 @@ async def get_current_state(
         }
 
     async def get_current_state_ids(
-        self, room_id: str, latest_event_ids: Optional[Iterable[str]] = None
+        self, room_id: str, latest_event_ids: Optional[Collection[str]] = None
     ) -> StateMap[str]:
         """Get the current state, or the state at a set of events, for a room
 
@@ -243,7 +243,7 @@ async def get_current_hosts_in_room(self, room_id: str) -> Set[str]:
         return await self.get_hosts_in_room_at_events(room_id, event_ids)
 
     async def get_hosts_in_room_at_events(
-        self, room_id: str, event_ids: Iterable[str]
+        self, room_id: str, event_ids: Collection[str]
     ) -> Set[str]:
         """Get the hosts that were in a room at the given event ids
 
@@ -404,7 +404,7 @@ async def compute_event_context(
 
     @measure_func()
     async def resolve_state_groups_for_events(
-        self, room_id: str, event_ids: Iterable[str]
+        self, room_id: str, event_ids: Collection[str]
     ) -> _StateCacheEntry:
         """Given a list of event_ids this method fetches the state at each
         event, resolves conflicts between them and returns them.
diff --git a/synapse/storage/background_updates.py b/synapse/storage/background_updates.py
index d64910aded33..08c6eabc6d1a 100644
--- a/synapse/storage/background_updates.py
+++ b/synapse/storage/background_updates.py
@@ -60,18 +60,19 @@ class _BackgroundUpdateHandler:
 
 
 class _BackgroundUpdateContextManager:
-    BACKGROUND_UPDATE_INTERVAL_MS = 1000
-    BACKGROUND_UPDATE_DURATION_MS = 100
-
-    def __init__(self, sleep: bool, clock: Clock):
+    def __init__(
+        self, sleep: bool, clock: Clock, sleep_duration_ms: int, update_duration: int
+    ):
         self._sleep = sleep
         self._clock = clock
+        self._sleep_duration_ms = sleep_duration_ms
+        self._update_duration_ms = update_duration
 
     async def __aenter__(self) -> int:
         if self._sleep:
-            await self._clock.sleep(self.BACKGROUND_UPDATE_INTERVAL_MS / 1000)
+            await self._clock.sleep(self._sleep_duration_ms / 1000)
 
-        return self.BACKGROUND_UPDATE_DURATION_MS
+        return self._update_duration_ms
 
     async def __aexit__(self, *exc) -> None:
         pass
@@ -102,10 +103,12 @@ def average_items_per_ms(self) -> Optional[float]:
         Returns:
             A duration in ms as a float
         """
-        if self.avg_duration_ms == 0:
-            return 0
-        elif self.total_item_count == 0:
+        # We want to return None if this is the first background update item
+        if self.total_item_count == 0:
             return None
+        # Avoid dividing by zero
+        elif self.avg_duration_ms == 0:
+            return 0
         else:
             # Use the exponential moving average so that we can adapt to
             # changes in how long the update process takes.
@@ -131,9 +134,6 @@ class BackgroundUpdater:
     process and autotuning the batch size.
     """
 
-    MINIMUM_BACKGROUND_BATCH_SIZE = 1
-    DEFAULT_BACKGROUND_BATCH_SIZE = 100
-
     def __init__(self, hs: "HomeServer", database: "DatabasePool"):
         self._clock = hs.get_clock()
         self.db_pool = database
@@ -158,6 +158,14 @@ def __init__(self, hs: "HomeServer", database: "DatabasePool"):
         # enable/disable background updates via the admin API.
         self.enabled = True
 
+        self.minimum_background_batch_size = hs.config.background_updates.min_batch_size
+        self.default_background_batch_size = (
+            hs.config.background_updates.default_batch_size
+        )
+        self.update_duration_ms = hs.config.background_updates.update_duration_ms
+        self.sleep_duration_ms = hs.config.background_updates.sleep_duration_ms
+        self.sleep_enabled = hs.config.background_updates.sleep_enabled
+
     def register_update_controller_callbacks(
         self,
         on_update: ON_UPDATE_CALLBACK,
@@ -214,7 +222,9 @@ def _get_context_manager_for_update(
         if self._on_update_callback is not None:
             return self._on_update_callback(update_name, database_name, oneshot)
 
-        return _BackgroundUpdateContextManager(sleep, self._clock)
+        return _BackgroundUpdateContextManager(
+            sleep, self._clock, self.sleep_duration_ms, self.update_duration_ms
+        )
 
     async def _default_batch_size(self, update_name: str, database_name: str) -> int:
         """The batch size to use for the first iteration of a new background
@@ -223,7 +233,7 @@ async def _default_batch_size(self, update_name: str, database_name: str) -> int
         if self._default_batch_size_callback is not None:
             return await self._default_batch_size_callback(update_name, database_name)
 
-        return self.DEFAULT_BACKGROUND_BATCH_SIZE
+        return self.default_background_batch_size
 
     async def _min_batch_size(self, update_name: str, database_name: str) -> int:
         """A lower bound on the batch size of a new background update.
@@ -233,7 +243,7 @@ async def _min_batch_size(self, update_name: str, database_name: str) -> int:
         if self._min_batch_size_callback is not None:
             return await self._min_batch_size_callback(update_name, database_name)
 
-        return self.MINIMUM_BACKGROUND_BATCH_SIZE
+        return self.minimum_background_batch_size
 
     def get_current_update(self) -> Optional[BackgroundUpdatePerformance]:
         """Returns the current background update, if any."""
@@ -252,9 +262,12 @@ def start_doing_background_updates(self) -> None:
         if self.enabled:
             # if we start a new background update, not all updates are done.
             self._all_done = False
-            run_as_background_process("background_updates", self.run_background_updates)
+            sleep = self.sleep_enabled
+            run_as_background_process(
+                "background_updates", self.run_background_updates, sleep
+            )
 
-    async def run_background_updates(self, sleep: bool = True) -> None:
+    async def run_background_updates(self, sleep: bool) -> None:
         if self._running or not self.enabled:
             return
 
diff --git a/synapse/storage/databases/main/cache.py b/synapse/storage/databases/main/cache.py
index c428dd5596af..d6a2df1afeb6 100644
--- a/synapse/storage/databases/main/cache.py
+++ b/synapse/storage/databases/main/cache.py
@@ -191,6 +191,10 @@ def _invalidate_caches_for_event(
 
         if redacts:
             self._invalidate_get_event_cache(redacts)
+            # Caches which might leak edits must be invalidated for the event being
+            # redacted.
+            self.get_relations_for_event.invalidate((redacts,))
+            self.get_applicable_edit.invalidate((redacts,))
 
         if etype == EventTypes.Member:
             self._membership_stream_cache.entity_has_changed(state_key, stream_ordering)
@@ -200,6 +204,8 @@ def _invalidate_caches_for_event(
             self.get_relations_for_event.invalidate((relates_to,))
             self.get_aggregation_groups_for_event.invalidate((relates_to,))
             self.get_applicable_edit.invalidate((relates_to,))
+            self.get_thread_summary.invalidate((relates_to,))
+            self.get_thread_participated.invalidate((relates_to,))
 
     async def invalidate_cache_and_stream(self, cache_name: str, keys: Tuple[Any, ...]):
         """Invalidates the cache and adds it to the cache stream so slaves
diff --git a/synapse/storage/databases/main/deviceinbox.py b/synapse/storage/databases/main/deviceinbox.py
index 1392363de15a..b4a1b041b1f8 100644
--- a/synapse/storage/databases/main/deviceinbox.py
+++ b/synapse/storage/databases/main/deviceinbox.py
@@ -298,6 +298,9 @@ async def _get_device_messages(
                 # This user has new messages sent to them. Query messages for them
                 user_ids_to_query.add(user_id)
 
+        if not user_ids_to_query:
+            return {}, to_stream_id
+
         def get_device_messages_txn(txn: LoggingTransaction):
             # Build a query to select messages from any of the given devices that
             # are between the given stream id bounds.
diff --git a/synapse/storage/databases/main/events.py b/synapse/storage/databases/main/events.py
index ca2a9ba9d116..1f60aef180d0 100644
--- a/synapse/storage/databases/main/events.py
+++ b/synapse/storage/databases/main/events.py
@@ -1518,7 +1518,7 @@ def _update_metadata_tables_txn(
                 )
 
                 # Remove from relations table.
-                self._handle_redaction(txn, event.redacts)
+                self._handle_redact_relations(txn, event.redacts)
 
         # Update the event_forward_extremities, event_backward_extremities and
         # event_edges tables.
@@ -1619,9 +1619,12 @@ def prefill():
 
         txn.call_after(prefill)
 
-    def _store_redaction(self, txn, event):
-        # invalidate the cache for the redacted event
+    def _store_redaction(self, txn: LoggingTransaction, event: EventBase) -> None:
+        # Invalidate the caches for the redacted event, note that these caches
+        # are also cleared as part of event replication in _invalidate_caches_for_event.
         txn.call_after(self.store._invalidate_get_event_cache, event.redacts)
+        txn.call_after(self.store.get_relations_for_event.invalidate, (event.redacts,))
+        txn.call_after(self.store.get_applicable_edit.invalidate, (event.redacts,))
 
         self.db_pool.simple_upsert_txn(
             txn,
@@ -1811,10 +1814,11 @@ def _handle_event_relations(
         if rel_type == RelationTypes.REPLACE:
             txn.call_after(self.store.get_applicable_edit.invalidate, (parent_id,))
 
-        if rel_type == RelationTypes.THREAD:
-            txn.call_after(
-                self.store.get_thread_summary.invalidate, (parent_id, event.room_id)
-            )
+        if (
+            rel_type == RelationTypes.THREAD
+            or rel_type == RelationTypes.UNSTABLE_THREAD
+        ):
+            txn.call_after(self.store.get_thread_summary.invalidate, (parent_id,))
             # It should be safe to only invalidate the cache if the user has not
             # previously participated in the thread, but that's difficult (and
             # potentially error-prone) so it is always invalidated.
@@ -1943,15 +1947,43 @@ def _handle_batch_event(self, txn: LoggingTransaction, event: EventBase):
 
         txn.execute(sql, (batch_id,))
 
-    def _handle_redaction(self, txn, redacted_event_id):
-        """Handles receiving a redaction and checking whether we need to remove
-        any redacted relations from the database.
+    def _handle_redact_relations(
+        self, txn: LoggingTransaction, redacted_event_id: str
+    ) -> None:
+        """Handles receiving a redaction and checking whether the redacted event
+        has any relations which must be removed from the database.
 
         Args:
             txn
-            redacted_event_id (str): The event that was redacted.
+            redacted_event_id: The event that was redacted.
         """
 
+        # Fetch the current relation of the event being redacted.
+        redacted_relates_to = self.db_pool.simple_select_one_onecol_txn(
+            txn,
+            table="event_relations",
+            keyvalues={"event_id": redacted_event_id},
+            retcol="relates_to_id",
+            allow_none=True,
+        )
+        # Any relation information for the related event must be cleared.
+        if redacted_relates_to is not None:
+            self.store._invalidate_cache_and_stream(
+                txn, self.store.get_relations_for_event, (redacted_relates_to,)
+            )
+            self.store._invalidate_cache_and_stream(
+                txn, self.store.get_aggregation_groups_for_event, (redacted_relates_to,)
+            )
+            self.store._invalidate_cache_and_stream(
+                txn, self.store.get_applicable_edit, (redacted_relates_to,)
+            )
+            self.store._invalidate_cache_and_stream(
+                txn, self.store.get_thread_summary, (redacted_relates_to,)
+            )
+            self.store._invalidate_cache_and_stream(
+                txn, self.store.get_thread_participated, (redacted_relates_to,)
+            )
+
         self.db_pool.simple_delete_txn(
             txn, table="event_relations", keyvalues={"event_id": redacted_event_id}
         )
diff --git a/synapse/storage/databases/main/events_worker.py b/synapse/storage/databases/main/events_worker.py
index 26784f755e40..59454a47dfdd 100644
--- a/synapse/storage/databases/main/events_worker.py
+++ b/synapse/storage/databases/main/events_worker.py
@@ -1286,7 +1286,7 @@ async def have_seen_events(
         )
         return {eid for ((_rid, eid), have_event) in res.items() if have_event}
 
-    @cachedList("have_seen_event", "keys")
+    @cachedList(cached_method_name="have_seen_event", list_name="keys")
     async def _have_seen_events_dict(
         self, keys: Iterable[Tuple[str, str]]
     ) -> Dict[Tuple[str, str], bool]:
@@ -1954,7 +1954,7 @@ def get_event_id_for_timestamp_txn(txn: LoggingTransaction) -> Optional[str]:
             get_event_id_for_timestamp_txn,
         )
 
-    @cachedList("is_partial_state_event", list_name="event_ids")
+    @cachedList(cached_method_name="is_partial_state_event", list_name="event_ids")
     async def get_partial_state_events(
         self, event_ids: Collection[str]
     ) -> Dict[str, bool]:
diff --git a/synapse/storage/databases/main/registration.py b/synapse/storage/databases/main/registration.py
index dc6665237abf..a698d10cc535 100644
--- a/synapse/storage/databases/main/registration.py
+++ b/synapse/storage/databases/main/registration.py
@@ -48,8 +48,6 @@ class ExternalIDReuseException(Exception):
     """Exception if writing an external id for a user fails,
     because this external id is given to an other user."""
 
-    pass
-
 
 @attr.s(frozen=True, slots=True, auto_attribs=True)
 class TokenLookupResult:
diff --git a/synapse/storage/databases/main/relations.py b/synapse/storage/databases/main/relations.py
index 36aa1092f602..c4869d64e663 100644
--- a/synapse/storage/databases/main/relations.py
+++ b/synapse/storage/databases/main/relations.py
@@ -91,10 +91,11 @@ def __init__(
 
         self._msc3440_enabled = hs.config.experimental.msc3440_enabled
 
-    @cached(tree=True)
+    @cached(uncached_args=("event",), tree=True)
     async def get_relations_for_event(
         self,
         event_id: str,
+        event: EventBase,
         room_id: str,
         relation_type: Optional[str] = None,
         event_type: Optional[str] = None,
@@ -108,6 +109,7 @@ async def get_relations_for_event(
 
         Args:
             event_id: Fetch events that relate to this event ID.
+            event: The matching EventBase to event_id.
             room_id: The room the event belongs to.
             relation_type: Only fetch events with this relation type, if given.
             event_type: Only fetch events with this event type, if given.
@@ -122,9 +124,13 @@ async def get_relations_for_event(
             List of event IDs that match relations requested. The rows are of
             the form `{"event_id": "..."}`.
         """
+        # We don't use `event_id`, it's there so that we can cache based on
+        # it. The `event_id` must match the `event.event_id`.
+        assert event.event_id == event_id
 
         where_clause = ["relates_to_id = ?", "room_id = ?"]
-        where_args: List[Union[str, int]] = [event_id, room_id]
+        where_args: List[Union[str, int]] = [event.event_id, room_id]
+        is_redacted = event.internal_metadata.is_redacted()
 
         if relation_type is not None:
             where_clause.append("relation_type = ?")
@@ -157,7 +163,7 @@ async def get_relations_for_event(
             order = "ASC"
 
         sql = """
-            SELECT event_id, topological_ordering, stream_ordering
+            SELECT event_id, relation_type, topological_ordering, stream_ordering
             FROM event_relations
             INNER JOIN events USING (event_id)
             WHERE %s
@@ -178,9 +184,12 @@ def _get_recent_references_for_event_txn(
             last_stream_id = None
             events = []
             for row in txn:
-                events.append({"event_id": row[0]})
-                last_topo_id = row[1]
-                last_stream_id = row[2]
+                # Do not include edits for redacted events as they leak event
+                # content.
+                if not is_redacted or row[1] != RelationTypes.REPLACE:
+                    events.append({"event_id": row[0]})
+                last_topo_id = row[2]
+                last_stream_id = row[3]
 
             # If there are more events, generate the next pagination key.
             next_token = None
@@ -499,7 +508,7 @@ def _get_thread_summaries_txn(
                         AND parent.room_id = child.room_id
                     WHERE
                         %s
-                        AND relation_type = ?
+                        AND %s
                     ORDER BY parent.event_id, child.topological_ordering DESC, child.stream_ordering DESC
                 """
             else:
@@ -514,16 +523,22 @@ def _get_thread_summaries_txn(
                         AND parent.room_id = child.room_id
                     WHERE
                         %s
-                        AND relation_type = ?
+                        AND %s
                     ORDER BY child.topological_ordering DESC, child.stream_ordering DESC
                 """
 
             clause, args = make_in_list_sql_clause(
                 txn.database_engine, "relates_to_id", event_ids
             )
-            args.append(RelationTypes.THREAD)
 
-            txn.execute(sql % (clause,), args)
+            if self._msc3440_enabled:
+                relations_clause = "(relation_type = ? OR relation_type = ?)"
+                args.extend((RelationTypes.THREAD, RelationTypes.UNSTABLE_THREAD))
+            else:
+                relations_clause = "relation_type = ?"
+                args.append(RelationTypes.THREAD)
+
+            txn.execute(sql % (clause, relations_clause), args)
             latest_event_ids = {}
             for parent_event_id, child_event_id in txn:
                 # Only consider the latest threaded reply (by topological ordering).
@@ -543,7 +558,7 @@ def _get_thread_summaries_txn(
                     AND parent.room_id = child.room_id
                 WHERE
                     %s
-                    AND relation_type = ?
+                    AND %s
                 GROUP BY parent.event_id
             """
 
@@ -552,9 +567,15 @@ def _get_thread_summaries_txn(
             clause, args = make_in_list_sql_clause(
                 txn.database_engine, "relates_to_id", latest_event_ids.keys()
             )
-            args.append(RelationTypes.THREAD)
 
-            txn.execute(sql % (clause,), args)
+            if self._msc3440_enabled:
+                relations_clause = "(relation_type = ? OR relation_type = ?)"
+                args.extend((RelationTypes.THREAD, RelationTypes.UNSTABLE_THREAD))
+            else:
+                relations_clause = "relation_type = ?"
+                args.append(RelationTypes.THREAD)
+
+            txn.execute(sql % (clause, relations_clause), args)
             counts = dict(cast(List[Tuple[str, int]], txn.fetchall()))
 
             return counts, latest_event_ids
@@ -617,16 +638,24 @@ def _get_thread_summary_txn(txn: LoggingTransaction) -> Set[str]:
                     AND parent.room_id = child.room_id
                 WHERE
                     %s
-                    AND relation_type = ?
+                    AND %s
                     AND child.sender = ?
             """
 
             clause, args = make_in_list_sql_clause(
                 txn.database_engine, "relates_to_id", event_ids
             )
-            args.extend((RelationTypes.THREAD, user_id))
 
-            txn.execute(sql % (clause,), args)
+            if self._msc3440_enabled:
+                relations_clause = "(relation_type = ? OR relation_type = ?)"
+                args.extend((RelationTypes.THREAD, RelationTypes.UNSTABLE_THREAD))
+            else:
+                relations_clause = "relation_type = ?"
+                args.append(RelationTypes.THREAD)
+
+            args.append(user_id)
+
+            txn.execute(sql % (clause, relations_clause), args)
             return {row[0] for row in txn.fetchall()}
 
         participated_threads = await self.db_pool.runInteraction(
@@ -776,7 +805,7 @@ async def _get_bundled_aggregation_for_event(
             )
 
         references = await self.get_relations_for_event(
-            event_id, room_id, RelationTypes.REFERENCE, direction="f"
+            event_id, event, room_id, RelationTypes.REFERENCE, direction="f"
         )
         if references.chunk:
             aggregations.references = await references.to_dict(cast("DataStore", self))
@@ -797,59 +826,51 @@ async def get_bundled_aggregations(
             A map of event ID to the bundled aggregation for the event. Not all
             events may have bundled aggregations in the results.
         """
-        # The already processed event IDs. Tracked separately from the result
-        # since the result omits events which do not have bundled aggregations.
-        seen_event_ids = set()
-
-        # State events and redacted events do not get bundled aggregations.
-        events = [
-            event
-            for event in events
-            if not event.is_state() and not event.internal_metadata.is_redacted()
-        ]
+        # De-duplicate events by ID to handle the same event requested multiple times.
+        #
+        # State events do not get bundled aggregations.
+        events_by_id = {
+            event.event_id: event for event in events if not event.is_state()
+        }
 
         # event ID -> bundled aggregation in non-serialized form.
         results: Dict[str, BundledAggregations] = {}
 
         # Fetch other relations per event.
-        for event in events:
-            # De-duplicate events by ID to handle the same event requested multiple
-            # times. The caches that _get_bundled_aggregation_for_event use should
-            # capture this, but best to reduce work.
-            if event.event_id in seen_event_ids:
-                continue
-            seen_event_ids.add(event.event_id)
-
+        for event in events_by_id.values():
             event_result = await self._get_bundled_aggregation_for_event(event, user_id)
             if event_result:
                 results[event.event_id] = event_result
 
-        # Fetch any edits.
-        edits = await self._get_applicable_edits(seen_event_ids)
+        # Fetch any edits (but not for redacted events).
+        edits = await self._get_applicable_edits(
+            [
+                event_id
+                for event_id, event in events_by_id.items()
+                if not event.internal_metadata.is_redacted()
+            ]
+        )
         for event_id, edit in edits.items():
             results.setdefault(event_id, BundledAggregations()).replace = edit
 
         # Fetch thread summaries.
-        if self._msc3440_enabled:
-            summaries = await self._get_thread_summaries(seen_event_ids)
-            # Only fetch participated for a limited selection based on what had
-            # summaries.
-            participated = await self._get_threads_participated(
-                summaries.keys(), user_id
-            )
-            for event_id, summary in summaries.items():
-                if summary:
-                    thread_count, latest_thread_event, edit = summary
-                    results.setdefault(
-                        event_id, BundledAggregations()
-                    ).thread = _ThreadAggregation(
-                        latest_event=latest_thread_event,
-                        latest_edit=edit,
-                        count=thread_count,
-                        # If there's a thread summary it must also exist in the
-                        # participated dictionary.
-                        current_user_participated=participated[event_id],
-                    )
+        summaries = await self._get_thread_summaries(events_by_id.keys())
+        # Only fetch participated for a limited selection based on what had
+        # summaries.
+        participated = await self._get_threads_participated(summaries.keys(), user_id)
+        for event_id, summary in summaries.items():
+            if summary:
+                thread_count, latest_thread_event, edit = summary
+                results.setdefault(
+                    event_id, BundledAggregations()
+                ).thread = _ThreadAggregation(
+                    latest_event=latest_thread_event,
+                    latest_edit=edit,
+                    count=thread_count,
+                    # If there's a thread summary it must also exist in the
+                    # participated dictionary.
+                    current_user_participated=participated[event_id],
+                )
 
         return results
 
diff --git a/synapse/storage/databases/main/roommember.py b/synapse/storage/databases/main/roommember.py
index e48ec5f495af..bef675b8453c 100644
--- a/synapse/storage/databases/main/roommember.py
+++ b/synapse/storage/databases/main/roommember.py
@@ -46,7 +46,7 @@
     ProfileInfo,
     RoomsForUser,
 )
-from synapse.types import PersistedEventPosition, StateMap, get_domain_from_id
+from synapse.types import PersistedEventPosition, get_domain_from_id
 from synapse.util.async_helpers import Linearizer
 from synapse.util.caches import intern_string
 from synapse.util.caches.descriptors import _CacheContext, cached, cachedList
@@ -273,7 +273,7 @@ def _get_room_summary_txn(txn):
             txn.execute(sql, (room_id,))
             res = {}
             for count, membership in txn:
-                summary = res.setdefault(membership, MemberSummary([], count))
+                res.setdefault(membership, MemberSummary([], count))
 
             # we order by membership and then fairly arbitrarily by event_id so
             # heroes are consistent
@@ -839,18 +839,14 @@ async def get_joined_hosts(self, room_id: str, state_entry):
 
         with Measure(self._clock, "get_joined_hosts"):
             return await self._get_joined_hosts(
-                room_id, state_group, state_entry.state, state_entry=state_entry
+                room_id, state_group, state_entry=state_entry
             )
 
     @cached(num_args=2, max_entries=10000, iterable=True)
     async def _get_joined_hosts(
-        self,
-        room_id: str,
-        state_group: int,
-        current_state_ids: StateMap[str],
-        state_entry: "_StateCacheEntry",
+        self, room_id: str, state_group: int, state_entry: "_StateCacheEntry"
     ) -> FrozenSet[str]:
-        # We don't use `state_group`, its there so that we can cache based on
+        # We don't use `state_group`, it's there so that we can cache based on
         # it. However, its important that its never None, since two
         # current_state's with a state_group of None are likely to be different.
         #
diff --git a/synapse/storage/databases/main/search.py b/synapse/storage/databases/main/search.py
index e23b1190726b..c5e9010c83b5 100644
--- a/synapse/storage/databases/main/search.py
+++ b/synapse/storage/databases/main/search.py
@@ -125,9 +125,6 @@ def __init__(
     ):
         super().__init__(database, db_conn, hs)
 
-        if not hs.config.server.enable_search:
-            return
-
         self.db_pool.updates.register_background_update_handler(
             self.EVENT_SEARCH_UPDATE_NAME, self._background_reindex_search
         )
@@ -243,9 +240,13 @@ def reindex_search_txn(txn):
 
             return len(event_search_rows)
 
-        result = await self.db_pool.runInteraction(
-            self.EVENT_SEARCH_UPDATE_NAME, reindex_search_txn
-        )
+        if self.hs.config.server.enable_search:
+            result = await self.db_pool.runInteraction(
+                self.EVENT_SEARCH_UPDATE_NAME, reindex_search_txn
+            )
+        else:
+            # Don't index anything if search is not enabled.
+            result = 0
 
         if not result:
             await self.db_pool.updates._end_background_update(
diff --git a/synapse/storage/databases/main/stream.py b/synapse/storage/databases/main/stream.py
index a898f847e7d5..39e1efe37348 100644
--- a/synapse/storage/databases/main/stream.py
+++ b/synapse/storage/databases/main/stream.py
@@ -325,21 +325,23 @@ def filter_to_clause(event_filter: Optional[Filter]) -> Tuple[str, List[str]]:
         args.extend(event_filter.labels)
 
     # Filter on relation_senders / relation types from the joined tables.
-    if event_filter.relation_senders:
+    if event_filter.related_by_senders:
         clauses.append(
             "(%s)"
             % " OR ".join(
-                "related_event.sender = ?" for _ in event_filter.relation_senders
+                "related_event.sender = ?" for _ in event_filter.related_by_senders
             )
         )
-        args.extend(event_filter.relation_senders)
+        args.extend(event_filter.related_by_senders)
 
-    if event_filter.relation_types:
+    if event_filter.related_by_rel_types:
         clauses.append(
             "(%s)"
-            % " OR ".join("relation_type = ?" for _ in event_filter.relation_types)
+            % " OR ".join(
+                "relation_type = ?" for _ in event_filter.related_by_rel_types
+            )
         )
-        args.extend(event_filter.relation_types)
+        args.extend(event_filter.related_by_rel_types)
 
     return " AND ".join(clauses), args
 
@@ -1203,7 +1205,7 @@ def _paginate_room_events_txn(
         # If there is a filter on relation_senders and relation_types join to the
         # relations table.
         if event_filter and (
-            event_filter.relation_senders or event_filter.relation_types
+            event_filter.related_by_senders or event_filter.related_by_rel_types
         ):
             # Filtering by relations could cause the same event to appear multiple
             # times (since there's no limit on the number of relations to an event).
@@ -1211,7 +1213,7 @@ def _paginate_room_events_txn(
             join_clause += """
                 LEFT JOIN event_relations AS relation ON (event.event_id = relation.relates_to_id)
             """
-            if event_filter.relation_senders:
+            if event_filter.related_by_senders:
                 join_clause += """
                     LEFT JOIN events AS related_event ON (relation.event_id = related_event.event_id)
                 """
diff --git a/synapse/storage/relations.py b/synapse/storage/relations.py
index 36ca2b827398..fba270150b63 100644
--- a/synapse/storage/relations.py
+++ b/synapse/storage/relations.py
@@ -54,37 +54,6 @@ async def to_dict(self, store: "DataStore") -> Dict[str, Any]:
         return d
 
 
-@attr.s(frozen=True, slots=True, auto_attribs=True)
-class RelationPaginationToken:
-    """Pagination token for relation pagination API.
-
-    As the results are in topological order, we can use the
-    `topological_ordering` and `stream_ordering` fields of the events at the
-    boundaries of the chunk as pagination tokens.
-
-    Attributes:
-        topological: The topological ordering of the boundary event
-        stream: The stream ordering of the boundary event.
-    """
-
-    topological: int
-    stream: int
-
-    @staticmethod
-    def from_string(string: str) -> "RelationPaginationToken":
-        try:
-            t, s = string.split("-")
-            return RelationPaginationToken(int(t), int(s))
-        except ValueError:
-            raise SynapseError(400, "Invalid relation pagination token")
-
-    async def to_string(self, store: "DataStore") -> str:
-        return "%d-%d" % (self.topological, self.stream)
-
-    def as_tuple(self) -> Tuple[Any, ...]:
-        return attr.astuple(self)
-
-
 @attr.s(frozen=True, slots=True, auto_attribs=True)
 class AggregationPaginationToken:
     """Pagination token for relation aggregation pagination API.
diff --git a/synapse/storage/schema/main/delta/30/as_users.py b/synapse/storage/schema/main/delta/30/as_users.py
index 22a7901e15df..4b4b166e37a6 100644
--- a/synapse/storage/schema/main/delta/30/as_users.py
+++ b/synapse/storage/schema/main/delta/30/as_users.py
@@ -36,7 +36,6 @@ def run_upgrade(cur, database_engine, config, *args, **kwargs):
         config_files = config.appservice.app_service_config_files
     except AttributeError:
         logger.warning("Could not get app_service_config_files from config")
-        pass
 
     appservices = load_appservices(config.server.server_name, config_files)
 
diff --git a/synapse/storage/state.py b/synapse/storage/state.py
index e79ecf64a0ec..86f1a5373bad 100644
--- a/synapse/storage/state.py
+++ b/synapse/storage/state.py
@@ -561,7 +561,7 @@ async def get_state_group_delta(
         return state_group_delta.prev_group, state_group_delta.delta_ids
 
     async def get_state_groups_ids(
-        self, _room_id: str, event_ids: Iterable[str]
+        self, _room_id: str, event_ids: Collection[str]
     ) -> Dict[int, MutableStateMap[str]]:
         """Get the event IDs of all the state for the state groups for the given events
 
@@ -596,7 +596,7 @@ async def get_state_ids_for_group(self, state_group: int) -> StateMap[str]:
         return group_to_state[state_group]
 
     async def get_state_groups(
-        self, room_id: str, event_ids: Iterable[str]
+        self, room_id: str, event_ids: Collection[str]
     ) -> Dict[int, List[EventBase]]:
         """Get the state groups for the given list of event_ids
 
@@ -648,7 +648,7 @@ def _get_state_groups_from_groups(
         return self.stores.state._get_state_groups_from_groups(groups, state_filter)
 
     async def get_state_for_events(
-        self, event_ids: Iterable[str], state_filter: Optional[StateFilter] = None
+        self, event_ids: Collection[str], state_filter: Optional[StateFilter] = None
     ) -> Dict[str, StateMap[EventBase]]:
         """Given a list of event_ids and type tuples, return a list of state
         dicts for each event.
@@ -684,7 +684,7 @@ async def get_state_for_events(
         return {event: event_to_state[event] for event in event_ids}
 
     async def get_state_ids_for_events(
-        self, event_ids: Iterable[str], state_filter: Optional[StateFilter] = None
+        self, event_ids: Collection[str], state_filter: Optional[StateFilter] = None
     ) -> Dict[str, StateMap[str]]:
         """
         Get the state dicts corresponding to a list of events, containing the event_ids
diff --git a/synapse/util/__init__.py b/synapse/util/__init__.py
index 58b4220ff355..d8046b7553cb 100644
--- a/synapse/util/__init__.py
+++ b/synapse/util/__init__.py
@@ -31,13 +31,6 @@
 if typing.TYPE_CHECKING:
     pass
 
-# FIXME Mjolnir imports glob_to_regex from this file, but it was moved to
-#       matrix_common.
-#       As a temporary workaround, we import glob_to_regex here for
-#       compatibility with current versions of Mjolnir.
-# See https://github.com/matrix-org/mjolnir/pull/174
-from matrix_common.regex import glob_to_regex  # noqa
-
 logger = logging.getLogger(__name__)
 
 
diff --git a/synapse/util/async_helpers.py b/synapse/util/async_helpers.py
index 60c03a66fd16..6a8e844d6365 100644
--- a/synapse/util/async_helpers.py
+++ b/synapse/util/async_helpers.py
@@ -18,9 +18,10 @@
 import inspect
 import itertools
 import logging
-from contextlib import contextmanager
+from contextlib import asynccontextmanager, contextmanager
 from typing import (
     Any,
+    AsyncIterator,
     Awaitable,
     Callable,
     Collection,
@@ -40,7 +41,7 @@
 )
 
 import attr
-from typing_extensions import ContextManager
+from typing_extensions import AsyncContextManager, Literal
 
 from twisted.internet import defer
 from twisted.internet.defer import CancelledError
@@ -96,6 +97,10 @@ class ObservableDeferred(Generic[_T], AbstractObservableDeferred[_T]):
 
     __slots__ = ["_deferred", "_observers", "_result"]
 
+    _deferred: "defer.Deferred[_T]"
+    _observers: Union[List["defer.Deferred[_T]"], Tuple[()]]
+    _result: Union[None, Tuple[Literal[True], _T], Tuple[Literal[False], Failure]]
+
     def __init__(self, deferred: "defer.Deferred[_T]", consumeErrors: bool = False):
         object.__setattr__(self, "_deferred", deferred)
         object.__setattr__(self, "_result", None)
@@ -158,12 +163,14 @@ def observe(self) -> "defer.Deferred[_T]":
         effect the underlying deferred.
         """
         if not self._result:
+            assert isinstance(self._observers, list)
             d: "defer.Deferred[_T]" = defer.Deferred()
             self._observers.append(d)
             return d
+        elif self._result[0]:
+            return defer.succeed(self._result[1])
         else:
-            success, res = self._result
-            return defer.succeed(res) if success else defer.fail(res)
+            return defer.fail(self._result[1])
 
     def observers(self) -> "Collection[defer.Deferred[_T]]":
         return self._observers
@@ -175,6 +182,8 @@ def has_succeeded(self) -> bool:
         return self._result is not None and self._result[0] is True
 
     def get_result(self) -> Union[_T, Failure]:
+        if self._result is None:
+            raise ValueError(f"{self!r} has no result yet")
         return self._result[1]
 
     def __getattr__(self, name: str) -> Any:
@@ -483,7 +492,7 @@ class ReadWriteLock:
 
     Example:
 
-        with await read_write_lock.read("test_key"):
+        async with read_write_lock.read("test_key"):
             # do some work
     """
 
@@ -506,22 +515,24 @@ def __init__(self) -> None:
         # Latest writer queued
         self.key_to_current_writer: Dict[str, defer.Deferred] = {}
 
-    async def read(self, key: str) -> ContextManager:
-        new_defer: "defer.Deferred[None]" = defer.Deferred()
-
-        curr_readers = self.key_to_current_readers.setdefault(key, set())
-        curr_writer = self.key_to_current_writer.get(key, None)
+    def read(self, key: str) -> AsyncContextManager:
+        @asynccontextmanager
+        async def _ctx_manager() -> AsyncIterator[None]:
+            new_defer: "defer.Deferred[None]" = defer.Deferred()
 
-        curr_readers.add(new_defer)
+            curr_readers = self.key_to_current_readers.setdefault(key, set())
+            curr_writer = self.key_to_current_writer.get(key, None)
 
-        # We wait for the latest writer to finish writing. We can safely ignore
-        # any existing readers... as they're readers.
-        if curr_writer:
-            await make_deferred_yieldable(curr_writer)
+            curr_readers.add(new_defer)
 
-        @contextmanager
-        def _ctx_manager() -> Iterator[None]:
             try:
+                # We wait for the latest writer to finish writing. We can safely ignore
+                # any existing readers... as they're readers.
+                # May raise a `CancelledError` if the `Deferred` wrapping us is
+                # cancelled. The `Deferred` we are waiting on must not be cancelled,
+                # since we do not own it.
+                if curr_writer:
+                    await make_deferred_yieldable(stop_cancellation(curr_writer))
                 yield
             finally:
                 with PreserveLoggingContext():
@@ -530,29 +541,35 @@ def _ctx_manager() -> Iterator[None]:
 
         return _ctx_manager()
 
-    async def write(self, key: str) -> ContextManager:
-        new_defer: "defer.Deferred[None]" = defer.Deferred()
+    def write(self, key: str) -> AsyncContextManager:
+        @asynccontextmanager
+        async def _ctx_manager() -> AsyncIterator[None]:
+            new_defer: "defer.Deferred[None]" = defer.Deferred()
 
-        curr_readers = self.key_to_current_readers.get(key, set())
-        curr_writer = self.key_to_current_writer.get(key, None)
+            curr_readers = self.key_to_current_readers.get(key, set())
+            curr_writer = self.key_to_current_writer.get(key, None)
 
-        # We wait on all latest readers and writer.
-        to_wait_on = list(curr_readers)
-        if curr_writer:
-            to_wait_on.append(curr_writer)
+            # We wait on all latest readers and writer.
+            to_wait_on = list(curr_readers)
+            if curr_writer:
+                to_wait_on.append(curr_writer)
 
-        # We can clear the list of current readers since the new writer waits
-        # for them to finish.
-        curr_readers.clear()
-        self.key_to_current_writer[key] = new_defer
+            # We can clear the list of current readers since `new_defer` waits
+            # for them to finish.
+            curr_readers.clear()
+            self.key_to_current_writer[key] = new_defer
 
-        await make_deferred_yieldable(defer.gatherResults(to_wait_on))
-
-        @contextmanager
-        def _ctx_manager() -> Iterator[None]:
+            to_wait_on_defer = defer.gatherResults(to_wait_on)
             try:
+                # Wait for all current readers and the latest writer to finish.
+                # May raise a `CancelledError` immediately after the wait if the
+                # `Deferred` wrapping us is cancelled. We must only release the lock
+                # once we have acquired it, hence the use of `delay_cancellation`
+                # rather than `stop_cancellation`.
+                await make_deferred_yieldable(delay_cancellation(to_wait_on_defer))
                 yield
             finally:
+                # Release the lock.
                 with PreserveLoggingContext():
                     new_defer.callback(None)
                 # `self.key_to_current_writer[key]` may be missing if there was another
@@ -678,12 +695,48 @@ def stop_cancellation(deferred: "defer.Deferred[T]") -> "defer.Deferred[T]":
             Synapse logcontext rules.
 
     Returns:
-        A new `Deferred`, which will contain the result of the original `Deferred`,
-        but will not propagate cancellation through to the original. When cancelled,
-        the new `Deferred` will fail with a `CancelledError` and will not follow the
-        Synapse logcontext rules. `make_deferred_yieldable` should be used to wrap
-        the new `Deferred`.
+        A new `Deferred`, which will contain the result of the original `Deferred`.
+        The new `Deferred` will not propagate cancellation through to the original.
+        When cancelled, the new `Deferred` will fail with a `CancelledError`.
+
+        The new `Deferred` will not follow the Synapse logcontext rules and should be
+        wrapped with `make_deferred_yieldable`.
     """
-    new_deferred: defer.Deferred[T] = defer.Deferred()
+    new_deferred: "defer.Deferred[T]" = defer.Deferred()
+    deferred.chainDeferred(new_deferred)
+    return new_deferred
+
+
+def delay_cancellation(deferred: "defer.Deferred[T]") -> "defer.Deferred[T]":
+    """Delay cancellation of a `Deferred` until it resolves.
+
+    Has the same effect as `stop_cancellation`, but the returned `Deferred` will not
+    resolve with a `CancelledError` until the original `Deferred` resolves.
+
+    Args:
+        deferred: The `Deferred` to protect against cancellation. May optionally follow
+            the Synapse logcontext rules.
+
+    Returns:
+        A new `Deferred`, which will contain the result of the original `Deferred`.
+        The new `Deferred` will not propagate cancellation through to the original.
+        When cancelled, the new `Deferred` will wait until the original `Deferred`
+        resolves before failing with a `CancelledError`.
+
+        The new `Deferred` will follow the Synapse logcontext rules if `deferred`
+        follows the Synapse logcontext rules. Otherwise the new `Deferred` should be
+        wrapped with `make_deferred_yieldable`.
+    """
+
+    def handle_cancel(new_deferred: "defer.Deferred[T]") -> None:
+        # before the new deferred is cancelled, we `pause` it to stop the cancellation
+        # propagating. we then `unpause` it once the wrapped deferred completes, to
+        # propagate the exception.
+        new_deferred.pause()
+        new_deferred.errback(Failure(CancelledError()))
+
+        deferred.addBoth(lambda _: new_deferred.unpause())
+
+    new_deferred: "defer.Deferred[T]" = defer.Deferred(handle_cancel)
     deferred.chainDeferred(new_deferred)
     return new_deferred
diff --git a/synapse/util/caches/descriptors.py b/synapse/util/caches/descriptors.py
index 1cdead02f14b..eda92d864dea 100644
--- a/synapse/util/caches/descriptors.py
+++ b/synapse/util/caches/descriptors.py
@@ -20,6 +20,7 @@
     Any,
     Awaitable,
     Callable,
+    Collection,
     Dict,
     Generic,
     Hashable,
@@ -40,6 +41,7 @@
 
 from synapse.logging.context import make_deferred_yieldable, preserve_fn
 from synapse.util import unwrapFirstError
+from synapse.util.async_helpers import delay_cancellation
 from synapse.util.caches.deferred_cache import DeferredCache
 from synapse.util.caches.lrucache import LruCache
 
@@ -69,6 +71,7 @@ def __init__(
         self,
         orig: Callable[..., Any],
         num_args: Optional[int],
+        uncached_args: Optional[Collection[str]] = None,
         cache_context: bool = False,
     ):
         self.orig = orig
@@ -76,6 +79,13 @@ def __init__(
         arg_spec = inspect.getfullargspec(orig)
         all_args = arg_spec.args
 
+        # There's no reason that keyword-only arguments couldn't be supported,
+        # but right now they're buggy so do not allow them.
+        if arg_spec.kwonlyargs:
+            raise ValueError(
+                "_CacheDescriptorBase does not support keyword-only arguments."
+            )
+
         if "cache_context" in all_args:
             if not cache_context:
                 raise ValueError(
@@ -88,6 +98,9 @@ def __init__(
                 " named `cache_context`"
             )
 
+        if num_args is not None and uncached_args is not None:
+            raise ValueError("Cannot provide both num_args and uncached_args")
+
         if num_args is None:
             num_args = len(all_args) - 1
             if cache_context:
@@ -105,6 +118,12 @@ def __init__(
         # list of the names of the args used as the cache key
         self.arg_names = all_args[1 : num_args + 1]
 
+        # If there are args to not cache on, filter them out (and fix the size of num_args).
+        if uncached_args is not None:
+            include_arg_in_cache_key = [n not in uncached_args for n in self.arg_names]
+        else:
+            include_arg_in_cache_key = [True] * len(self.arg_names)
+
         # self.arg_defaults is a map of arg name to its default value for each
         # argument that has a default value
         if arg_spec.defaults:
@@ -119,8 +138,8 @@ def __init__(
 
         self.add_cache_context = cache_context
 
-        self.cache_key_builder = get_cache_key_builder(
-            self.arg_names, self.arg_defaults
+        self.cache_key_builder = _get_cache_key_builder(
+            self.arg_names, include_arg_in_cache_key, self.arg_defaults
         )
 
 
@@ -130,8 +149,7 @@ class _LruCachedFunction(Generic[F]):
 
 
 def lru_cache(
-    max_entries: int = 1000,
-    cache_context: bool = False,
+    *, max_entries: int = 1000, cache_context: bool = False
 ) -> Callable[[F], _LruCachedFunction[F]]:
     """A method decorator that applies a memoizing cache around the function.
 
@@ -186,7 +204,9 @@ def __init__(
         max_entries: int = 1000,
         cache_context: bool = False,
     ):
-        super().__init__(orig, num_args=None, cache_context=cache_context)
+        super().__init__(
+            orig, num_args=None, uncached_args=None, cache_context=cache_context
+        )
         self.max_entries = max_entries
 
     def __get__(self, obj: Optional[Any], owner: Optional[Type]) -> Callable[..., Any]:
@@ -260,6 +280,9 @@ def foo(self, key, cache_context):
         num_args: number of positional arguments (excluding ``self`` and
             ``cache_context``) to use as cache keys. Defaults to all named
             args of the function.
+        uncached_args: a list of argument names to not use as the cache key.
+            (``self`` and ``cache_context`` are always ignored.) Cannot be used
+            with num_args.
         tree:
         cache_context:
         iterable:
@@ -273,12 +296,18 @@ def __init__(
         orig: Callable[..., Any],
         max_entries: int = 1000,
         num_args: Optional[int] = None,
+        uncached_args: Optional[Collection[str]] = None,
         tree: bool = False,
         cache_context: bool = False,
         iterable: bool = False,
         prune_unread_entries: bool = True,
     ):
-        super().__init__(orig, num_args=num_args, cache_context=cache_context)
+        super().__init__(
+            orig,
+            num_args=num_args,
+            uncached_args=uncached_args,
+            cache_context=cache_context,
+        )
 
         if tree and self.num_args < 2:
             raise RuntimeError(
@@ -322,6 +351,11 @@ def _wrapped(*args: Any, **kwargs: Any) -> Any:
                 ret = defer.maybeDeferred(preserve_fn(self.orig), obj, *args, **kwargs)
                 ret = cache.set(cache_key, ret, callback=invalidate_callback)
 
+                # We started a new call to `self.orig`, so we must always wait for it to
+                # complete. Otherwise we might mark our current logging context as
+                # finished while `self.orig` is still using it in the background.
+                ret = delay_cancellation(ret)
+
             return make_deferred_yieldable(ret)
 
         wrapped = cast(_CachedFunction, _wrapped)
@@ -369,7 +403,7 @@ def __init__(
                 but including list_name) to use as cache keys. Defaults to all
                 named args of the function.
         """
-        super().__init__(orig, num_args=num_args)
+        super().__init__(orig, num_args=num_args, uncached_args=None)
 
         self.list_name = list_name
 
@@ -482,6 +516,11 @@ def errback_all(f: Failure) -> None:
                 d = defer.gatherResults(cached_defers, consumeErrors=True).addCallbacks(
                     lambda _: results, unwrapFirstError
                 )
+                if missing:
+                    # We started a new call to `self.orig`, so we must always wait for it to
+                    # complete. Otherwise we might mark our current logging context as
+                    # finished while `self.orig` is still using it in the background.
+                    d = delay_cancellation(d)
                 return make_deferred_yieldable(d)
             else:
                 return defer.succeed(results)
@@ -530,8 +569,10 @@ def get_instance(
 
 
 def cached(
+    *,
     max_entries: int = 1000,
     num_args: Optional[int] = None,
+    uncached_args: Optional[Collection[str]] = None,
     tree: bool = False,
     cache_context: bool = False,
     iterable: bool = False,
@@ -541,6 +582,7 @@ def cached(
         orig,
         max_entries=max_entries,
         num_args=num_args,
+        uncached_args=uncached_args,
         tree=tree,
         cache_context=cache_context,
         iterable=iterable,
@@ -551,7 +593,7 @@ def cached(
 
 
 def cachedList(
-    cached_method_name: str, list_name: str, num_args: Optional[int] = None
+    *, cached_method_name: str, list_name: str, num_args: Optional[int] = None
 ) -> Callable[[F], _CachedFunction[F]]:
     """Creates a descriptor that wraps a function in a `CacheListDescriptor`.
 
@@ -590,13 +632,16 @@ def batch_do_something(self, first_arg, second_args):
     return cast(Callable[[F], _CachedFunction[F]], func)
 
 
-def get_cache_key_builder(
-    param_names: Sequence[str], param_defaults: Mapping[str, Any]
+def _get_cache_key_builder(
+    param_names: Sequence[str],
+    include_params: Sequence[bool],
+    param_defaults: Mapping[str, Any],
 ) -> Callable[[Sequence[Any], Mapping[str, Any]], CacheKey]:
     """Construct a function which will build cache keys suitable for a cached function
 
     Args:
         param_names: list of formal parameter names for the cached function
+        include_params: list of bools of whether to include the parameter name in the cache key
         param_defaults: a mapping from parameter name to default value for that param
 
     Returns:
@@ -608,6 +653,7 @@ def get_cache_key_builder(
 
     if len(param_names) == 1:
         nm = param_names[0]
+        assert include_params[0] is True
 
         def get_cache_key(args: Sequence[Any], kwargs: Mapping[str, Any]) -> CacheKey:
             if nm in kwargs:
@@ -620,13 +666,18 @@ def get_cache_key(args: Sequence[Any], kwargs: Mapping[str, Any]) -> CacheKey:
     else:
 
         def get_cache_key(args: Sequence[Any], kwargs: Mapping[str, Any]) -> CacheKey:
-            return tuple(_get_cache_key_gen(param_names, param_defaults, args, kwargs))
+            return tuple(
+                _get_cache_key_gen(
+                    param_names, include_params, param_defaults, args, kwargs
+                )
+            )
 
     return get_cache_key
 
 
 def _get_cache_key_gen(
     param_names: Iterable[str],
+    include_params: Iterable[bool],
     param_defaults: Mapping[str, Any],
     args: Sequence[Any],
     kwargs: Mapping[str, Any],
@@ -637,16 +688,18 @@ def _get_cache_key_gen(
     This is essentially the same operation as `inspect.getcallargs`, but optimised so
     that we don't need to inspect the target function for each call.
     """
-
     # We loop through each arg name, looking up if its in the `kwargs`,
     # otherwise using the next argument in `args`. If there are no more
     # args then we try looking the arg name up in the defaults.
     pos = 0
-    for nm in param_names:
+    for nm, inc in zip(param_names, include_params):
         if nm in kwargs:
-            yield kwargs[nm]
+            if inc:
+                yield kwargs[nm]
         elif pos < len(args):
-            yield args[pos]
+            if inc:
+                yield args[pos]
             pos += 1
         else:
-            yield param_defaults[nm]
+            if inc:
+                yield param_defaults[nm]
diff --git a/synapse/util/caches/treecache.py b/synapse/util/caches/treecache.py
index 563845f86769..e78305f78746 100644
--- a/synapse/util/caches/treecache.py
+++ b/synapse/util/caches/treecache.py
@@ -22,8 +22,6 @@ class TreeCacheNode(dict):
     leaves.
     """
 
-    pass
-
 
 class TreeCache:
     """
diff --git a/synapse/util/templates.py b/synapse/util/templates.py
index 12941065ca60..fb758b7180f2 100644
--- a/synapse/util/templates.py
+++ b/synapse/util/templates.py
@@ -64,6 +64,7 @@ def build_jinja_env(
         {
             "format_ts": _format_ts_filter,
             "mxc_to_http": _create_mxc_to_http_filter(config.server.public_baseurl),
+            "localpart_from_email": _localpart_from_email_filter,
         }
     )
 
@@ -112,3 +113,7 @@ def mxc_to_http_filter(
 
 def _format_ts_filter(value: int, format: str) -> str:
     return time.strftime(format, time.localtime(value / 1000))
+
+
+def _localpart_from_email_filter(address: str) -> str:
+    return address.rsplit("@", 1)[0]
diff --git a/synapse/visibility.py b/synapse/visibility.py
index 1b970ce479d0..281cbe4d8877 100644
--- a/synapse/visibility.py
+++ b/synapse/visibility.py
@@ -81,8 +81,9 @@ async def filter_events_for_client(
 
     types = ((EventTypes.RoomHistoryVisibility, ""), (EventTypes.Member, user_id))
 
+    # we exclude outliers at this point, and then handle them separately later
     event_id_to_state = await storage.state.get_state_for_events(
-        frozenset(e.event_id for e in events),
+        frozenset(e.event_id for e in events if not e.internal_metadata.outlier),
         state_filter=StateFilter.from_types(types),
     )
 
@@ -154,6 +155,17 @@ def allowed(event: EventBase) -> Optional[EventBase]:
         if event.event_id in always_include_ids:
             return event
 
+        # we need to handle outliers separately, since we don't have the room state.
+        if event.internal_metadata.outlier:
+            # Normally these can't be seen by clients, but we make an exception for
+            # for out-of-band membership events (eg, incoming invites, or rejections of
+            # said invite) for the user themselves.
+            if event.type == EventTypes.Member and event.state_key == user_id:
+                logger.debug("Returning out-of-band-membership event %s", event)
+                return event
+
+            return None
+
         state = event_id_to_state[event.event_id]
 
         # get the room_visibility at the time of the event.
@@ -198,6 +210,9 @@ def allowed(event: EventBase) -> Optional[EventBase]:
 
             # Always allow the user to see their own leave events, otherwise
             # they won't see the room disappear if they reject the invite
+            #
+            # (Note this doesn't work for out-of-band invite rejections, which don't
+            # have prev_state populated. They are handled above in the outlier code.)
             if membership == "leave" and (
                 prev_membership == "join" or prev_membership == "invite"
             ):
diff --git a/tests/appservice/test_appservice.py b/tests/appservice/test_appservice.py
index 9bd6275e92db..edc584d0cf50 100644
--- a/tests/appservice/test_appservice.py
+++ b/tests/appservice/test_appservice.py
@@ -36,7 +36,10 @@ def setUp(self):
             hostname="matrix.org",  # only used by get_groups_for_user
         )
         self.event = Mock(
-            type="m.something", room_id="!foo:bar", sender="@someone:somewhere"
+            event_id="$abc:xyz",
+            type="m.something",
+            room_id="!foo:bar",
+            sender="@someone:somewhere",
         )
 
         self.store = Mock()
@@ -50,7 +53,9 @@ def test_regex_user_id_prefix_match(self):
         self.assertTrue(
             (
                 yield defer.ensureDeferred(
-                    self.service.is_interested(self.event, self.store)
+                    self.service.is_interested_in_event(
+                        self.event.event_id, self.event, self.store
+                    )
                 )
             )
         )
@@ -62,7 +67,9 @@ def test_regex_user_id_prefix_no_match(self):
         self.assertFalse(
             (
                 yield defer.ensureDeferred(
-                    self.service.is_interested(self.event, self.store)
+                    self.service.is_interested_in_event(
+                        self.event.event_id, self.event, self.store
+                    )
                 )
             )
         )
@@ -76,7 +83,9 @@ def test_regex_room_member_is_checked(self):
         self.assertTrue(
             (
                 yield defer.ensureDeferred(
-                    self.service.is_interested(self.event, self.store)
+                    self.service.is_interested_in_event(
+                        self.event.event_id, self.event, self.store
+                    )
                 )
             )
         )
@@ -90,7 +99,9 @@ def test_regex_room_id_match(self):
         self.assertTrue(
             (
                 yield defer.ensureDeferred(
-                    self.service.is_interested(self.event, self.store)
+                    self.service.is_interested_in_event(
+                        self.event.event_id, self.event, self.store
+                    )
                 )
             )
         )
@@ -104,7 +115,9 @@ def test_regex_room_id_no_match(self):
         self.assertFalse(
             (
                 yield defer.ensureDeferred(
-                    self.service.is_interested(self.event, self.store)
+                    self.service.is_interested_in_event(
+                        self.event.event_id, self.event, self.store
+                    )
                 )
             )
         )
@@ -121,7 +134,9 @@ def test_regex_alias_match(self):
         self.assertTrue(
             (
                 yield defer.ensureDeferred(
-                    self.service.is_interested(self.event, self.store)
+                    self.service.is_interested_in_event(
+                        self.event.event_id, self.event, self.store
+                    )
                 )
             )
         )
@@ -174,7 +189,9 @@ def test_regex_alias_no_match(self):
         self.assertFalse(
             (
                 yield defer.ensureDeferred(
-                    self.service.is_interested(self.event, self.store)
+                    self.service.is_interested_in_event(
+                        self.event.event_id, self.event, self.store
+                    )
                 )
             )
         )
@@ -191,7 +208,9 @@ def test_regex_multiple_matches(self):
         self.assertTrue(
             (
                 yield defer.ensureDeferred(
-                    self.service.is_interested(self.event, self.store)
+                    self.service.is_interested_in_event(
+                        self.event.event_id, self.event, self.store
+                    )
                 )
             )
         )
@@ -207,7 +226,9 @@ def test_interested_in_self(self):
         self.assertTrue(
             (
                 yield defer.ensureDeferred(
-                    self.service.is_interested(self.event, self.store)
+                    self.service.is_interested_in_event(
+                        self.event.event_id, self.event, self.store
+                    )
                 )
             )
         )
@@ -225,7 +246,9 @@ def test_member_list_match(self):
         self.assertTrue(
             (
                 yield defer.ensureDeferred(
-                    self.service.is_interested(event=self.event, store=self.store)
+                    self.service.is_interested_in_event(
+                        self.event.event_id, self.event, self.store
+                    )
                 )
             )
         )
diff --git a/tests/config/test_background_update.py b/tests/config/test_background_update.py
new file mode 100644
index 000000000000..0c32c1ca299e
--- /dev/null
+++ b/tests/config/test_background_update.py
@@ -0,0 +1,58 @@
+# Copyright 2022 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+import yaml
+
+from synapse.storage.background_updates import BackgroundUpdater
+
+from tests.unittest import HomeserverTestCase, override_config
+
+
+class BackgroundUpdateConfigTestCase(HomeserverTestCase):
+    # Tests that the default values in the config are correctly loaded. Note that the default
+    # values are loaded when the corresponding config options are commented out, which is why there isn't
+    # a config specified here.
+    def test_default_configuration(self):
+        background_updater = BackgroundUpdater(
+            self.hs, self.hs.get_datastores().main.db_pool
+        )
+
+        self.assertEqual(background_updater.minimum_background_batch_size, 1)
+        self.assertEqual(background_updater.default_background_batch_size, 100)
+        self.assertEqual(background_updater.sleep_enabled, True)
+        self.assertEqual(background_updater.sleep_duration_ms, 1000)
+        self.assertEqual(background_updater.update_duration_ms, 100)
+
+    # Tests that non-default values for the config options are properly picked up and passed on.
+    @override_config(
+        yaml.safe_load(
+            """
+            background_updates:
+                background_update_duration_ms: 1000
+                sleep_enabled: false
+                sleep_duration_ms: 600
+                min_batch_size: 5
+                default_batch_size: 50
+            """
+        )
+    )
+    def test_custom_configuration(self):
+        background_updater = BackgroundUpdater(
+            self.hs, self.hs.get_datastores().main.db_pool
+        )
+
+        self.assertEqual(background_updater.minimum_background_batch_size, 5)
+        self.assertEqual(background_updater.default_background_batch_size, 50)
+        self.assertEqual(background_updater.sleep_enabled, False)
+        self.assertEqual(background_updater.sleep_duration_ms, 600)
+        self.assertEqual(background_updater.update_duration_ms, 1000)
diff --git a/tests/events/test_utils.py b/tests/events/test_utils.py
index 45e3395b3361..00ad19e446db 100644
--- a/tests/events/test_utils.py
+++ b/tests/events/test_utils.py
@@ -16,6 +16,7 @@
 from synapse.api.room_versions import RoomVersions
 from synapse.events import make_event_from_dict
 from synapse.events.utils import (
+    SerializeEventConfig,
     copy_power_levels_contents,
     prune_event,
     serialize_event,
@@ -392,7 +393,9 @@ def test_member(self):
 
 class SerializeEventTestCase(unittest.TestCase):
     def serialize(self, ev, fields):
-        return serialize_event(ev, 1479807801915, only_event_fields=fields)
+        return serialize_event(
+            ev, 1479807801915, config=SerializeEventConfig(only_event_fields=fields)
+        )
 
     def test_event_fields_works_with_keys(self):
         self.assertEqual(
diff --git a/tests/federation/test_federation_sender.py b/tests/federation/test_federation_sender.py
index 60e0c31f4384..e90592855ad9 100644
--- a/tests/federation/test_federation_sender.py
+++ b/tests/federation/test_federation_sender.py
@@ -201,9 +201,12 @@ def test_send_device_updates(self):
         self.assertEqual(len(self.edus), 1)
         stream_id = self.check_device_update_edu(self.edus.pop(0), u1, "D1", None)
 
+        # We queue up device list updates to be sent over federation, so we
+        # advance to clear the queue.
+        self.reactor.advance(1)
+
         # a second call should produce no new device EDUs
         self.hs.get_federation_sender().send_device_messages("host2")
-        self.pump()
         self.assertEqual(self.edus, [])
 
         # a second device
@@ -232,6 +235,10 @@ def test_upload_signatures(self):
         device1_signing_key = self.generate_and_upload_device_signing_key(u1, "D1")
         device2_signing_key = self.generate_and_upload_device_signing_key(u1, "D2")
 
+        # We queue up device list updates to be sent over federation, so we
+        # advance to clear the queue.
+        self.reactor.advance(1)
+
         # expect two more edus
         self.assertEqual(len(self.edus), 2)
         stream_id = self.check_device_update_edu(self.edus.pop(0), u1, "D1", stream_id)
@@ -265,6 +272,10 @@ def test_upload_signatures(self):
             e2e_handler.upload_signing_keys_for_user(u1, cross_signing_keys)
         )
 
+        # We queue up device list updates to be sent over federation, so we
+        # advance to clear the queue.
+        self.reactor.advance(1)
+
         # expect signing key update edu
         self.assertEqual(len(self.edus), 2)
         self.assertEqual(self.edus.pop(0)["edu_type"], "m.signing_key_update")
@@ -284,6 +295,10 @@ def test_upload_signatures(self):
         )
         self.assertEqual(ret["failures"], {})
 
+        # We queue up device list updates to be sent over federation, so we
+        # advance to clear the queue.
+        self.reactor.advance(1)
+
         # expect two edus, in one or two transactions. We don't know what order the
         # devices will be updated.
         self.assertEqual(len(self.edus), 2)
@@ -307,6 +322,10 @@ def test_delete_devices(self):
         self.login("user", "pass", device_id="D2")
         self.login("user", "pass", device_id="D3")
 
+        # We queue up device list updates to be sent over federation, so we
+        # advance to clear the queue.
+        self.reactor.advance(1)
+
         # expect three edus
         self.assertEqual(len(self.edus), 3)
         stream_id = self.check_device_update_edu(self.edus.pop(0), u1, "D1", None)
@@ -318,6 +337,10 @@ def test_delete_devices(self):
             self.hs.get_device_handler().delete_devices(u1, ["D1", "D2", "D3"])
         )
 
+        # We queue up device list updates to be sent over federation, so we
+        # advance to clear the queue.
+        self.reactor.advance(1)
+
         # expect three edus, in an unknown order
         self.assertEqual(len(self.edus), 3)
         for edu in self.edus:
@@ -350,12 +373,19 @@ def test_unreachable_server(self):
             self.hs.get_device_handler().delete_devices(u1, ["D1", "D2", "D3"])
         )
 
+        # We queue up device list updates to be sent over federation, so we
+        # advance to clear the queue.
+        self.reactor.advance(1)
+
         self.assertGreaterEqual(mock_send_txn.call_count, 4)
 
         # recover the server
         mock_send_txn.side_effect = self.record_transaction
         self.hs.get_federation_sender().send_device_messages("host2")
-        self.pump()
+
+        # We queue up device list updates to be sent over federation, so we
+        # advance to clear the queue.
+        self.reactor.advance(1)
 
         # for each device, there should be a single update
         self.assertEqual(len(self.edus), 3)
@@ -390,6 +420,10 @@ def test_prune_outbound_device_pokes1(self):
             self.hs.get_device_handler().delete_devices(u1, ["D1", "D2", "D3"])
         )
 
+        # We queue up device list updates to be sent over federation, so we
+        # advance to clear the queue.
+        self.reactor.advance(1)
+
         self.assertGreaterEqual(mock_send_txn.call_count, 4)
 
         # run the prune job
@@ -401,7 +435,10 @@ def test_prune_outbound_device_pokes1(self):
         # recover the server
         mock_send_txn.side_effect = self.record_transaction
         self.hs.get_federation_sender().send_device_messages("host2")
-        self.pump()
+
+        # We queue up device list updates to be sent over federation, so we
+        # advance to clear the queue.
+        self.reactor.advance(1)
 
         # there should be a single update for this user.
         self.assertEqual(len(self.edus), 1)
@@ -435,6 +472,10 @@ def test_prune_outbound_device_pokes2(self):
         self.login("user", "pass", device_id="D2")
         self.login("user", "pass", device_id="D3")
 
+        # We queue up device list updates to be sent over federation, so we
+        # advance to clear the queue.
+        self.reactor.advance(1)
+
         # delete them again
         self.get_success(
             self.hs.get_device_handler().delete_devices(u1, ["D1", "D2", "D3"])
@@ -451,7 +492,10 @@ def test_prune_outbound_device_pokes2(self):
         # recover the server
         mock_send_txn.side_effect = self.record_transaction
         self.hs.get_federation_sender().send_device_messages("host2")
-        self.pump()
+
+        # We queue up device list updates to be sent over federation, so we
+        # advance to clear the queue.
+        self.reactor.advance(1)
 
         # ... and we should get a single update for this user.
         self.assertEqual(len(self.edus), 1)
diff --git a/tests/handlers/test_admin.py b/tests/handlers/test_admin.py
index abf2a0fe0dc5..c1579dac610f 100644
--- a/tests/handlers/test_admin.py
+++ b/tests/handlers/test_admin.py
@@ -15,11 +15,15 @@
 from collections import Counter
 from unittest.mock import Mock
 
+from twisted.test.proto_helpers import MemoryReactor
+
 import synapse.rest.admin
 import synapse.storage
 from synapse.api.constants import EventTypes, JoinRules
 from synapse.api.room_versions import RoomVersions
 from synapse.rest.client import knock, login, room
+from synapse.server import HomeServer
+from synapse.util import Clock
 
 from tests import unittest
 
@@ -32,7 +36,7 @@ class ExfiltrateData(unittest.HomeserverTestCase):
         knock.register_servlets,
     ]
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.admin_handler = hs.get_admin_handler()
 
         self.user1 = self.register_user("user1", "password")
@@ -41,7 +45,7 @@ def prepare(self, reactor, clock, hs):
         self.user2 = self.register_user("user2", "password")
         self.token2 = self.login("user2", "password")
 
-    def test_single_public_joined_room(self):
+    def test_single_public_joined_room(self) -> None:
         """Test that we write *all* events for a public room"""
         room_id = self.helper.create_room_as(
             self.user1, tok=self.token1, is_public=True
@@ -74,7 +78,7 @@ def test_single_public_joined_room(self):
         self.assertEqual(counter[(EventTypes.Member, self.user1)], 1)
         self.assertEqual(counter[(EventTypes.Member, self.user2)], 1)
 
-    def test_single_private_joined_room(self):
+    def test_single_private_joined_room(self) -> None:
         """Tests that we correctly write state when we can't see all events in
         a room.
         """
@@ -112,7 +116,7 @@ def test_single_private_joined_room(self):
         self.assertEqual(counter[(EventTypes.Member, self.user1)], 1)
         self.assertEqual(counter[(EventTypes.Member, self.user2)], 1)
 
-    def test_single_left_room(self):
+    def test_single_left_room(self) -> None:
         """Tests that we don't see events in the room after we leave."""
         room_id = self.helper.create_room_as(self.user1, tok=self.token1)
         self.helper.send(room_id, body="Hello!", tok=self.token1)
@@ -144,7 +148,7 @@ def test_single_left_room(self):
         self.assertEqual(counter[(EventTypes.Member, self.user1)], 1)
         self.assertEqual(counter[(EventTypes.Member, self.user2)], 2)
 
-    def test_single_left_rejoined_private_room(self):
+    def test_single_left_rejoined_private_room(self) -> None:
         """Tests that see the correct events in private rooms when we
         repeatedly join and leave.
         """
@@ -185,7 +189,7 @@ def test_single_left_rejoined_private_room(self):
         self.assertEqual(counter[(EventTypes.Member, self.user1)], 1)
         self.assertEqual(counter[(EventTypes.Member, self.user2)], 3)
 
-    def test_invite(self):
+    def test_invite(self) -> None:
         """Tests that pending invites get handled correctly."""
         room_id = self.helper.create_room_as(self.user1, tok=self.token1)
         self.helper.send(room_id, body="Hello!", tok=self.token1)
@@ -204,7 +208,7 @@ def test_invite(self):
         self.assertEqual(args[1].content["membership"], "invite")
         self.assertTrue(args[2])  # Assert there is at least one bit of state
 
-    def test_knock(self):
+    def test_knock(self) -> None:
         """Tests that knock get handled correctly."""
         # create a knockable v7 room
         room_id = self.helper.create_room_as(
diff --git a/tests/handlers/test_appservice.py b/tests/handlers/test_appservice.py
index 072e6bbcdd6e..cead9f90df56 100644
--- a/tests/handlers/test_appservice.py
+++ b/tests/handlers/test_appservice.py
@@ -59,11 +59,11 @@ def setUp(self):
         self.event_source = hs.get_event_sources()
 
     def test_notify_interested_services(self):
-        interested_service = self._mkservice(is_interested=True)
+        interested_service = self._mkservice(is_interested_in_event=True)
         services = [
-            self._mkservice(is_interested=False),
+            self._mkservice(is_interested_in_event=False),
             interested_service,
-            self._mkservice(is_interested=False),
+            self._mkservice(is_interested_in_event=False),
         ]
 
         self.mock_as_api.query_user.return_value = make_awaitable(True)
@@ -85,7 +85,7 @@ def test_notify_interested_services(self):
 
     def test_query_user_exists_unknown_user(self):
         user_id = "@someone:anywhere"
-        services = [self._mkservice(is_interested=True)]
+        services = [self._mkservice(is_interested_in_event=True)]
         services[0].is_interested_in_user.return_value = True
         self.mock_store.get_app_services.return_value = services
         self.mock_store.get_user_by_id.return_value = make_awaitable(None)
@@ -102,7 +102,7 @@ def test_query_user_exists_unknown_user(self):
 
     def test_query_user_exists_known_user(self):
         user_id = "@someone:anywhere"
-        services = [self._mkservice(is_interested=True)]
+        services = [self._mkservice(is_interested_in_event=True)]
         services[0].is_interested_in_user.return_value = True
         self.mock_store.get_app_services.return_value = services
         self.mock_store.get_user_by_id.return_value = make_awaitable({"name": user_id})
@@ -127,11 +127,11 @@ def test_query_room_alias_exists(self):
 
         room_id = "!alpha:bet"
         servers = ["aperture"]
-        interested_service = self._mkservice_alias(is_interested_in_alias=True)
+        interested_service = self._mkservice_alias(is_room_alias_in_namespace=True)
         services = [
-            self._mkservice_alias(is_interested_in_alias=False),
+            self._mkservice_alias(is_room_alias_in_namespace=False),
             interested_service,
-            self._mkservice_alias(is_interested_in_alias=False),
+            self._mkservice_alias(is_room_alias_in_namespace=False),
         ]
 
         self.mock_as_api.query_alias.return_value = make_awaitable(True)
@@ -275,7 +275,7 @@ def test_notify_interested_services_ephemeral(self):
         to be pushed out to interested appservices, and that the stream ID is
         updated accordingly.
         """
-        interested_service = self._mkservice(is_interested=True)
+        interested_service = self._mkservice(is_interested_in_event=True)
         services = [interested_service]
         self.mock_store.get_app_services.return_value = services
         self.mock_store.get_type_stream_id_for_appservice.return_value = make_awaitable(
@@ -304,7 +304,7 @@ def test_notify_interested_services_ephemeral_out_of_order(self):
         Test sending out of order ephemeral events to the appservice handler
         are ignored.
         """
-        interested_service = self._mkservice(is_interested=True)
+        interested_service = self._mkservice(is_interested_in_event=True)
         services = [interested_service]
 
         self.mock_store.get_app_services.return_value = services
@@ -325,17 +325,45 @@ def test_notify_interested_services_ephemeral_out_of_order(self):
             interested_service, ephemeral=[]
         )
 
-    def _mkservice(self, is_interested, protocols=None):
+    def _mkservice(
+        self, is_interested_in_event: bool, protocols: Optional[Iterable] = None
+    ) -> Mock:
+        """
+        Create a new mock representing an ApplicationService.
+
+        Args:
+            is_interested_in_event: Whether this application service will be considered
+                interested in all events.
+            protocols: The third-party protocols that this application service claims to
+                support.
+
+        Returns:
+            A mock representing the ApplicationService.
+        """
         service = Mock()
-        service.is_interested.return_value = make_awaitable(is_interested)
+        service.is_interested_in_event.return_value = make_awaitable(
+            is_interested_in_event
+        )
         service.token = "mock_service_token"
         service.url = "mock_service_url"
         service.protocols = protocols
         return service
 
-    def _mkservice_alias(self, is_interested_in_alias):
+    def _mkservice_alias(self, is_room_alias_in_namespace: bool) -> Mock:
+        """
+        Create a new mock representing an ApplicationService that is or is not interested
+        any given room aliase.
+
+        Args:
+            is_room_alias_in_namespace: If true, the application service will be interested
+                in all room aliases that are queried against it. If false, the application
+                service will not be interested in any room aliases.
+
+        Returns:
+            A mock representing the ApplicationService.
+        """
         service = Mock()
-        service.is_interested_in_alias.return_value = is_interested_in_alias
+        service.is_room_alias_in_namespace.return_value = is_room_alias_in_namespace
         service.token = "mock_service_token"
         service.url = "mock_service_url"
         return service
diff --git a/tests/handlers/test_auth.py b/tests/handlers/test_auth.py
index 0c6e55e72592..67a7829769b6 100644
--- a/tests/handlers/test_auth.py
+++ b/tests/handlers/test_auth.py
@@ -15,8 +15,12 @@
 
 import pymacaroons
 
+from twisted.test.proto_helpers import MemoryReactor
+
 from synapse.api.errors import AuthError, ResourceLimitError
 from synapse.rest import admin
+from synapse.server import HomeServer
+from synapse.util import Clock
 
 from tests import unittest
 from tests.test_utils import make_awaitable
@@ -27,7 +31,7 @@ class AuthTestCase(unittest.HomeserverTestCase):
         admin.register_servlets,
     ]
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.auth_handler = hs.get_auth_handler()
         self.macaroon_generator = hs.get_macaroon_generator()
 
@@ -42,23 +46,23 @@ def prepare(self, reactor, clock, hs):
 
         self.user1 = self.register_user("a_user", "pass")
 
-    def test_macaroon_caveats(self):
+    def test_macaroon_caveats(self) -> None:
         token = self.macaroon_generator.generate_guest_access_token("a_user")
         macaroon = pymacaroons.Macaroon.deserialize(token)
 
-        def verify_gen(caveat):
+        def verify_gen(caveat: str) -> bool:
             return caveat == "gen = 1"
 
-        def verify_user(caveat):
+        def verify_user(caveat: str) -> bool:
             return caveat == "user_id = a_user"
 
-        def verify_type(caveat):
+        def verify_type(caveat: str) -> bool:
             return caveat == "type = access"
 
-        def verify_nonce(caveat):
+        def verify_nonce(caveat: str) -> bool:
             return caveat.startswith("nonce =")
 
-        def verify_guest(caveat):
+        def verify_guest(caveat: str) -> bool:
             return caveat == "guest = true"
 
         v = pymacaroons.Verifier()
@@ -69,7 +73,7 @@ def verify_guest(caveat):
         v.satisfy_general(verify_guest)
         v.verify(macaroon, self.hs.config.key.macaroon_secret_key)
 
-    def test_short_term_login_token_gives_user_id(self):
+    def test_short_term_login_token_gives_user_id(self) -> None:
         token = self.macaroon_generator.generate_short_term_login_token(
             self.user1, "", duration_in_ms=5000
         )
@@ -84,7 +88,7 @@ def test_short_term_login_token_gives_user_id(self):
             AuthError,
         )
 
-    def test_short_term_login_token_gives_auth_provider(self):
+    def test_short_term_login_token_gives_auth_provider(self) -> None:
         token = self.macaroon_generator.generate_short_term_login_token(
             self.user1, auth_provider_id="my_idp"
         )
@@ -92,7 +96,7 @@ def test_short_term_login_token_gives_auth_provider(self):
         self.assertEqual(self.user1, res.user_id)
         self.assertEqual("my_idp", res.auth_provider_id)
 
-    def test_short_term_login_token_cannot_replace_user_id(self):
+    def test_short_term_login_token_cannot_replace_user_id(self) -> None:
         token = self.macaroon_generator.generate_short_term_login_token(
             self.user1, "", duration_in_ms=5000
         )
@@ -112,7 +116,7 @@ def test_short_term_login_token_cannot_replace_user_id(self):
             AuthError,
         )
 
-    def test_mau_limits_disabled(self):
+    def test_mau_limits_disabled(self) -> None:
         self.auth_blocking._limit_usage_by_mau = False
         # Ensure does not throw exception
         self.get_success(
@@ -127,7 +131,7 @@ def test_mau_limits_disabled(self):
             )
         )
 
-    def test_mau_limits_exceeded_large(self):
+    def test_mau_limits_exceeded_large(self) -> None:
         self.auth_blocking._limit_usage_by_mau = True
         self.hs.get_datastores().main.get_monthly_active_count = Mock(
             return_value=make_awaitable(self.large_number_of_users)
@@ -150,7 +154,7 @@ def test_mau_limits_exceeded_large(self):
             ResourceLimitError,
         )
 
-    def test_mau_limits_parity(self):
+    def test_mau_limits_parity(self) -> None:
         # Ensure we're not at the unix epoch.
         self.reactor.advance(1)
         self.auth_blocking._limit_usage_by_mau = True
@@ -189,7 +193,7 @@ def test_mau_limits_parity(self):
             )
         )
 
-    def test_mau_limits_not_exceeded(self):
+    def test_mau_limits_not_exceeded(self) -> None:
         self.auth_blocking._limit_usage_by_mau = True
 
         self.hs.get_datastores().main.get_monthly_active_count = Mock(
@@ -211,7 +215,7 @@ def test_mau_limits_not_exceeded(self):
             )
         )
 
-    def _get_macaroon(self):
+    def _get_macaroon(self) -> pymacaroons.Macaroon:
         token = self.macaroon_generator.generate_short_term_login_token(
             self.user1, "", duration_in_ms=5000
         )
diff --git a/tests/handlers/test_deactivate_account.py b/tests/handlers/test_deactivate_account.py
index ddda36c5a93b..3a107912265e 100644
--- a/tests/handlers/test_deactivate_account.py
+++ b/tests/handlers/test_deactivate_account.py
@@ -39,7 +39,7 @@ def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.user = self.register_user("user", "pass")
         self.token = self.login("user", "pass")
 
-    def _deactivate_my_account(self):
+    def _deactivate_my_account(self) -> None:
         """
         Deactivates the account `self.user` using `self.token` and asserts
         that it returns a 200 success code.
diff --git a/tests/handlers/test_device.py b/tests/handlers/test_device.py
index 683677fd0770..01ea7d2a4281 100644
--- a/tests/handlers/test_device.py
+++ b/tests/handlers/test_device.py
@@ -14,9 +14,14 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import synapse.api.errors
-import synapse.handlers.device
-import synapse.storage
+from typing import Optional
+
+from twisted.test.proto_helpers import MemoryReactor
+
+from synapse.api.errors import NotFoundError, SynapseError
+from synapse.handlers.device import MAX_DEVICE_DISPLAY_NAME_LEN
+from synapse.server import HomeServer
+from synapse.util import Clock
 
 from tests import unittest
 
@@ -25,28 +30,27 @@
 
 
 class DeviceTestCase(unittest.HomeserverTestCase):
-    def make_homeserver(self, reactor, clock):
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
         hs = self.setup_test_homeserver("server", federation_http_client=None)
         self.handler = hs.get_device_handler()
         self.store = hs.get_datastores().main
         return hs
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         # These tests assume that it starts 1000 seconds in.
         self.reactor.advance(1000)
 
-    def test_device_is_created_with_invalid_name(self):
+    def test_device_is_created_with_invalid_name(self) -> None:
         self.get_failure(
             self.handler.check_device_registered(
                 user_id="@boris:foo",
                 device_id="foo",
-                initial_device_display_name="a"
-                * (synapse.handlers.device.MAX_DEVICE_DISPLAY_NAME_LEN + 1),
+                initial_device_display_name="a" * (MAX_DEVICE_DISPLAY_NAME_LEN + 1),
             ),
-            synapse.api.errors.SynapseError,
+            SynapseError,
         )
 
-    def test_device_is_created_if_doesnt_exist(self):
+    def test_device_is_created_if_doesnt_exist(self) -> None:
         res = self.get_success(
             self.handler.check_device_registered(
                 user_id="@boris:foo",
@@ -59,7 +63,7 @@ def test_device_is_created_if_doesnt_exist(self):
         dev = self.get_success(self.handler.store.get_device("@boris:foo", "fco"))
         self.assertEqual(dev["display_name"], "display name")
 
-    def test_device_is_preserved_if_exists(self):
+    def test_device_is_preserved_if_exists(self) -> None:
         res1 = self.get_success(
             self.handler.check_device_registered(
                 user_id="@boris:foo",
@@ -81,7 +85,7 @@ def test_device_is_preserved_if_exists(self):
         dev = self.get_success(self.handler.store.get_device("@boris:foo", "fco"))
         self.assertEqual(dev["display_name"], "display name")
 
-    def test_device_id_is_made_up_if_unspecified(self):
+    def test_device_id_is_made_up_if_unspecified(self) -> None:
         device_id = self.get_success(
             self.handler.check_device_registered(
                 user_id="@theresa:foo",
@@ -93,7 +97,7 @@ def test_device_id_is_made_up_if_unspecified(self):
         dev = self.get_success(self.handler.store.get_device("@theresa:foo", device_id))
         self.assertEqual(dev["display_name"], "display")
 
-    def test_get_devices_by_user(self):
+    def test_get_devices_by_user(self) -> None:
         self._record_users()
 
         res = self.get_success(self.handler.get_devices_by_user(user1))
@@ -131,7 +135,7 @@ def test_get_devices_by_user(self):
             device_map["abc"],
         )
 
-    def test_get_device(self):
+    def test_get_device(self) -> None:
         self._record_users()
 
         res = self.get_success(self.handler.get_device(user1, "abc"))
@@ -146,21 +150,19 @@ def test_get_device(self):
             res,
         )
 
-    def test_delete_device(self):
+    def test_delete_device(self) -> None:
         self._record_users()
 
         # delete the device
         self.get_success(self.handler.delete_device(user1, "abc"))
 
         # check the device was deleted
-        self.get_failure(
-            self.handler.get_device(user1, "abc"), synapse.api.errors.NotFoundError
-        )
+        self.get_failure(self.handler.get_device(user1, "abc"), NotFoundError)
 
         # we'd like to check the access token was invalidated, but that's a
         # bit of a PITA.
 
-    def test_delete_device_and_device_inbox(self):
+    def test_delete_device_and_device_inbox(self) -> None:
         self._record_users()
 
         # add an device_inbox
@@ -191,7 +193,7 @@ def test_delete_device_and_device_inbox(self):
         )
         self.assertIsNone(res)
 
-    def test_update_device(self):
+    def test_update_device(self) -> None:
         self._record_users()
 
         update = {"display_name": "new display"}
@@ -200,32 +202,29 @@ def test_update_device(self):
         res = self.get_success(self.handler.get_device(user1, "abc"))
         self.assertEqual(res["display_name"], "new display")
 
-    def test_update_device_too_long_display_name(self):
+    def test_update_device_too_long_display_name(self) -> None:
         """Update a device with a display name that is invalid (too long)."""
         self._record_users()
 
         # Request to update a device display name with a new value that is longer than allowed.
-        update = {
-            "display_name": "a"
-            * (synapse.handlers.device.MAX_DEVICE_DISPLAY_NAME_LEN + 1)
-        }
+        update = {"display_name": "a" * (MAX_DEVICE_DISPLAY_NAME_LEN + 1)}
         self.get_failure(
             self.handler.update_device(user1, "abc", update),
-            synapse.api.errors.SynapseError,
+            SynapseError,
         )
 
         # Ensure the display name was not updated.
         res = self.get_success(self.handler.get_device(user1, "abc"))
         self.assertEqual(res["display_name"], "display 2")
 
-    def test_update_unknown_device(self):
+    def test_update_unknown_device(self) -> None:
         update = {"display_name": "new_display"}
         self.get_failure(
             self.handler.update_device("user_id", "unknown_device_id", update),
-            synapse.api.errors.NotFoundError,
+            NotFoundError,
         )
 
-    def _record_users(self):
+    def _record_users(self) -> None:
         # check this works for both devices which have a recorded client_ip,
         # and those which don't.
         self._record_user(user1, "xyz", "display 0")
@@ -238,8 +237,13 @@ def _record_users(self):
         self.reactor.advance(10000)
 
     def _record_user(
-        self, user_id, device_id, display_name, access_token=None, ip=None
-    ):
+        self,
+        user_id: str,
+        device_id: str,
+        display_name: str,
+        access_token: Optional[str] = None,
+        ip: Optional[str] = None,
+    ) -> None:
         device_id = self.get_success(
             self.handler.check_device_registered(
                 user_id=user_id,
@@ -248,7 +252,7 @@ def _record_user(
             )
         )
 
-        if ip is not None:
+        if access_token is not None and ip is not None:
             self.get_success(
                 self.store.insert_client_ip(
                     user_id, access_token, ip, "user_agent", device_id
@@ -258,7 +262,7 @@ def _record_user(
 
 
 class DehydrationTestCase(unittest.HomeserverTestCase):
-    def make_homeserver(self, reactor, clock):
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
         hs = self.setup_test_homeserver("server", federation_http_client=None)
         self.handler = hs.get_device_handler()
         self.registration = hs.get_registration_handler()
@@ -266,7 +270,7 @@ def make_homeserver(self, reactor, clock):
         self.store = hs.get_datastores().main
         return hs
 
-    def test_dehydrate_and_rehydrate_device(self):
+    def test_dehydrate_and_rehydrate_device(self) -> None:
         user_id = "@boris:dehydration"
 
         self.get_success(self.store.register_user(user_id, "foobar"))
@@ -303,7 +307,7 @@ def test_dehydrate_and_rehydrate_device(self):
                 access_token=access_token,
                 device_id="not the right device ID",
             ),
-            synapse.api.errors.NotFoundError,
+            NotFoundError,
         )
 
         # dehydrating the right devices should succeed and change our device ID
@@ -331,7 +335,7 @@ def test_dehydrate_and_rehydrate_device(self):
         # make sure that the device ID that we were initially assigned no longer exists
         self.get_failure(
             self.handler.get_device(user_id, device_id),
-            synapse.api.errors.NotFoundError,
+            NotFoundError,
         )
 
         # make sure that there's no device available for dehydrating now
diff --git a/tests/handlers/test_password_providers.py b/tests/handlers/test_password_providers.py
index 49d832de814d..d401fda93855 100644
--- a/tests/handlers/test_password_providers.py
+++ b/tests/handlers/test_password_providers.py
@@ -124,7 +124,6 @@ def __init__(self, config, api: ModuleApi):
                 ("m.login.password", ("password",)): self.check_auth,
             }
         )
-        pass
 
     def check_auth(self, *args):
         return mock_password_provider.check_auth(*args)
diff --git a/tests/handlers/test_room_summary.py b/tests/handlers/test_room_summary.py
index cff07a8973b3..d37292ce138e 100644
--- a/tests/handlers/test_room_summary.py
+++ b/tests/handlers/test_room_summary.py
@@ -172,6 +172,9 @@ def _assert_hierarchy(
         result_room_ids = []
         result_children_ids = []
         for result_room in result["rooms"]:
+            # Ensure federation results are not leaking over the client-server API.
+            self.assertNotIn("allowed_room_ids", result_room)
+
             result_room_ids.append(result_room["room_id"])
             result_children_ids.append(
                 [
diff --git a/tests/push/test_http.py b/tests/push/test_http.py
index c284beb37ce0..6691e0712896 100644
--- a/tests/push/test_http.py
+++ b/tests/push/test_http.py
@@ -11,6 +11,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+from typing import List, Tuple
 from unittest.mock import Mock
 
 from twisted.internet.defer import Deferred
@@ -18,7 +19,7 @@
 import synapse.rest.admin
 from synapse.logging.context import make_deferred_yieldable
 from synapse.push import PusherConfigException
-from synapse.rest.client import login, receipts, room
+from synapse.rest.client import login, push_rule, receipts, room
 
 from tests.unittest import HomeserverTestCase, override_config
 
@@ -29,6 +30,7 @@ class HTTPPusherTests(HomeserverTestCase):
         room.register_servlets,
         login.register_servlets,
         receipts.register_servlets,
+        push_rule.register_servlets,
     ]
     user_id = True
     hijack_auth = False
@@ -39,12 +41,12 @@ def default_config(self):
         return config
 
     def make_homeserver(self, reactor, clock):
-        self.push_attempts = []
+        self.push_attempts: List[tuple[Deferred, str, dict]] = []
 
         m = Mock()
 
         def post_json_get_json(url, body):
-            d = Deferred()
+            d: Deferred = Deferred()
             self.push_attempts.append((d, url, body))
             return make_deferred_yieldable(d)
 
@@ -719,3 +721,67 @@ def _send_read_request(self, access_token, message_event_id, room_id):
             access_token=access_token,
         )
         self.assertEqual(channel.code, 200, channel.json_body)
+
+    def _make_user_with_pusher(self, username: str) -> Tuple[str, str]:
+        user_id = self.register_user(username, "pass")
+        access_token = self.login(username, "pass")
+
+        # Register the pusher
+        user_tuple = self.get_success(
+            self.hs.get_datastores().main.get_user_by_access_token(access_token)
+        )
+        token_id = user_tuple.token_id
+
+        self.get_success(
+            self.hs.get_pusherpool().add_pusher(
+                user_id=user_id,
+                access_token=token_id,
+                kind="http",
+                app_id="m.http",
+                app_display_name="HTTP Push Notifications",
+                device_display_name="pushy push",
+                pushkey="a@example.com",
+                lang=None,
+                data={"url": "http://example.com/_matrix/push/v1/notify"},
+            )
+        )
+
+        return user_id, access_token
+
+    def test_dont_notify_rule_overrides_message(self):
+        """
+        The override push rule will suppress notification
+        """
+
+        user_id, access_token = self._make_user_with_pusher("user")
+        other_user_id, other_access_token = self._make_user_with_pusher("otheruser")
+
+        # Create a room
+        room = self.helper.create_room_as(user_id, tok=access_token)
+
+        # Disable user notifications for this room -> user
+        body = {
+            "conditions": [{"kind": "event_match", "key": "room_id", "pattern": room}],
+            "actions": ["dont_notify"],
+        }
+        channel = self.make_request(
+            "PUT",
+            "/pushrules/global/override/best.friend",
+            body,
+            access_token=access_token,
+        )
+        self.assertEqual(channel.code, 200)
+
+        # Check we start with no pushes
+        self.assertEqual(len(self.push_attempts), 0)
+
+        # The other user joins
+        self.helper.join(room=room, user=other_user_id, tok=other_access_token)
+
+        # The other user sends a message (ignored by dont_notify push rule set above)
+        self.helper.send(room, body="Hi!", tok=other_access_token)
+        self.assertEqual(len(self.push_attempts), 0)
+
+        # The user sends a message back (sends a notification)
+        self.helper.send(room, body="Hello", tok=access_token)
+        self.assertEqual(len(self.push_attempts), 1)
diff --git a/tests/replication/_base.py b/tests/replication/_base.py
index a7a05a564fe9..9c5df266bd1f 100644
--- a/tests/replication/_base.py
+++ b/tests/replication/_base.py
@@ -251,7 +251,7 @@ def setUp(self):
                 self.connect_any_redis_attempts,
             )
 
-            self.hs.get_tcp_replication().start_replication(self.hs)
+            self.hs.get_replication_command_handler().start_replication(self.hs)
 
         # When we see a connection attempt to the master replication listener we
         # automatically set up the connection. This is so that tests don't
@@ -375,7 +375,7 @@ def make_worker_hs(
         )
 
         if worker_hs.config.redis.redis_enabled:
-            worker_hs.get_tcp_replication().start_replication(worker_hs)
+            worker_hs.get_replication_command_handler().start_replication(worker_hs)
 
         return worker_hs
 
diff --git a/tests/replication/tcp/streams/test_events.py b/tests/replication/tcp/streams/test_events.py
index f9d5da723cce..641a94133b1d 100644
--- a/tests/replication/tcp/streams/test_events.py
+++ b/tests/replication/tcp/streams/test_events.py
@@ -420,7 +420,7 @@ def test_backwards_stream_id(self):
 
         # Manually send an old RDATA command, which should get dropped. This
         # re-uses the row from above, but with an earlier stream token.
-        self.hs.get_tcp_replication().send_command(
+        self.hs.get_replication_command_handler().send_command(
             RdataCommand("events", "master", 1, row)
         )
 
diff --git a/tests/replication/tcp/streams/test_typing.py b/tests/replication/tcp/streams/test_typing.py
index 3ff5afc6e501..9a229dd23f4a 100644
--- a/tests/replication/tcp/streams/test_typing.py
+++ b/tests/replication/tcp/streams/test_typing.py
@@ -118,7 +118,7 @@ def test_reset(self):
 
         # Reset the typing handler
         self.hs.get_replication_streams()["typing"].last_token = 0
-        self.hs.get_tcp_replication()._streams["typing"].last_token = 0
+        self.hs.get_replication_command_handler()._streams["typing"].last_token = 0
         typing._latest_room_serial = 0
         typing._typing_stream_change_cache = StreamChangeCache(
             "TypingStreamChangeCache", typing._latest_room_serial
diff --git a/tests/replication/test_federation_ack.py b/tests/replication/test_federation_ack.py
index 1b6a4bf4b0b1..26b8bd512a7f 100644
--- a/tests/replication/test_federation_ack.py
+++ b/tests/replication/test_federation_ack.py
@@ -48,7 +48,7 @@ def test_federation_ack_sent(self):
         transport, rather than assuming that the implementation has a
         ReplicationCommandHandler.
         """
-        rch = self.hs.get_tcp_replication()
+        rch = self.hs.get_replication_command_handler()
 
         # wire up the ReplicationCommandHandler to a mock connection, which needs
         # to implement IReplicationConnection. (Note that Mock doesn't understand
diff --git a/tests/rest/admin/test_background_updates.py b/tests/rest/admin/test_background_updates.py
index fb36aa994090..6cf56b1e352f 100644
--- a/tests/rest/admin/test_background_updates.py
+++ b/tests/rest/admin/test_background_updates.py
@@ -39,6 +39,7 @@ def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.store = hs.get_datastores().main
         self.admin_user = self.register_user("admin", "pass", admin=True)
         self.admin_user_tok = self.login("admin", "pass")
+        self.updater = BackgroundUpdater(hs, self.store.db_pool)
 
     @parameterized.expand(
         [
@@ -135,10 +136,10 @@ def test_status_bg_update(self) -> None:
         """Test the status API works with a background update."""
 
         # Create a new background update
-
         self._register_bg_update()
 
         self.store.db_pool.updates.start_doing_background_updates()
+
         self.reactor.pump([1.0, 1.0, 1.0])
 
         channel = self.make_request(
@@ -155,10 +156,10 @@ def test_status_bg_update(self) -> None:
                 "current_updates": {
                     "master": {
                         "name": "test_update",
-                        "average_items_per_ms": 0.001,
+                        "average_items_per_ms": 0.1,
                         "total_duration_ms": 1000.0,
                         "total_item_count": (
-                            BackgroundUpdater.MINIMUM_BACKGROUND_BATCH_SIZE
+                            self.updater.default_background_batch_size
                         ),
                     }
                 },
@@ -210,10 +211,10 @@ def test_enabled(self) -> None:
                 "current_updates": {
                     "master": {
                         "name": "test_update",
-                        "average_items_per_ms": 0.001,
+                        "average_items_per_ms": 0.1,
                         "total_duration_ms": 1000.0,
                         "total_item_count": (
-                            BackgroundUpdater.MINIMUM_BACKGROUND_BATCH_SIZE
+                            self.updater.default_background_batch_size
                         ),
                     }
                 },
@@ -239,10 +240,10 @@ def test_enabled(self) -> None:
                 "current_updates": {
                     "master": {
                         "name": "test_update",
-                        "average_items_per_ms": 0.001,
+                        "average_items_per_ms": 0.1,
                         "total_duration_ms": 1000.0,
                         "total_item_count": (
-                            BackgroundUpdater.MINIMUM_BACKGROUND_BATCH_SIZE
+                            self.updater.default_background_batch_size
                         ),
                     }
                 },
@@ -278,11 +279,9 @@ def test_enabled(self) -> None:
                 "current_updates": {
                     "master": {
                         "name": "test_update",
-                        "average_items_per_ms": 0.001,
+                        "average_items_per_ms": 0.05263157894736842,
                         "total_duration_ms": 2000.0,
-                        "total_item_count": (
-                            2 * BackgroundUpdater.MINIMUM_BACKGROUND_BATCH_SIZE
-                        ),
+                        "total_item_count": (110),
                     }
                 },
                 "enabled": True,
diff --git a/tests/rest/client/test_account.py b/tests/rest/client/test_account.py
index 6c4462e74a53..def836054db1 100644
--- a/tests/rest/client/test_account.py
+++ b/tests/rest/client/test_account.py
@@ -15,11 +15,12 @@
 import os
 import re
 from email.parser import Parser
-from typing import Dict, List, Optional
+from typing import Any, Dict, List, Optional, Union
 from unittest.mock import Mock
 
 import pkg_resources
 
+from twisted.internet.interfaces import IReactorTCP
 from twisted.test.proto_helpers import MemoryReactor
 
 import synapse.rest.admin
@@ -30,6 +31,7 @@
 from synapse.rest.client import account, login, register, room
 from synapse.rest.synapse.client.password_reset import PasswordResetSubmitTokenResource
 from synapse.server import HomeServer
+from synapse.types import JsonDict
 from synapse.util import Clock
 
 from tests import unittest
@@ -46,7 +48,7 @@ class PasswordResetTestCase(unittest.HomeserverTestCase):
         login.register_servlets,
     ]
 
-    def make_homeserver(self, reactor, clock):
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
         config = self.default_config()
 
         # Email config.
@@ -67,20 +69,27 @@ def make_homeserver(self, reactor, clock):
         hs = self.setup_test_homeserver(config=config)
 
         async def sendmail(
-            reactor, smtphost, smtpport, from_addr, to_addrs, msg, **kwargs
-        ):
-            self.email_attempts.append(msg)
-
-        self.email_attempts = []
+            reactor: IReactorTCP,
+            smtphost: str,
+            smtpport: int,
+            from_addr: str,
+            to_addr: str,
+            msg_bytes: bytes,
+            *args: Any,
+            **kwargs: Any,
+        ) -> None:
+            self.email_attempts.append(msg_bytes)
+
+        self.email_attempts: List[bytes] = []
         hs.get_send_email_handler()._sendmail = sendmail
 
         return hs
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.store = hs.get_datastores().main
         self.submit_token_resource = PasswordResetSubmitTokenResource(hs)
 
-    def test_basic_password_reset(self):
+    def test_basic_password_reset(self) -> None:
         """Test basic password reset flow"""
         old_password = "monkey"
         new_password = "kangeroo"
@@ -118,7 +127,7 @@ def test_basic_password_reset(self):
         self.attempt_wrong_password_login("kermit", old_password)
 
     @override_config({"rc_3pid_validation": {"burst_count": 3}})
-    def test_ratelimit_by_email(self):
+    def test_ratelimit_by_email(self) -> None:
         """Test that we ratelimit /requestToken for the same email."""
         old_password = "monkey"
         new_password = "kangeroo"
@@ -139,7 +148,7 @@ def test_ratelimit_by_email(self):
             )
         )
 
-        def reset(ip):
+        def reset(ip: str) -> None:
             client_secret = "foobar"
             session_id = self._request_token(email, client_secret, ip)
 
@@ -166,7 +175,7 @@ def reset(ip):
 
         self.assertEqual(cm.exception.code, 429)
 
-    def test_basic_password_reset_canonicalise_email(self):
+    def test_basic_password_reset_canonicalise_email(self) -> None:
         """Test basic password reset flow
         Request password reset with different spelling
         """
@@ -206,7 +215,7 @@ def test_basic_password_reset_canonicalise_email(self):
         # Assert we can't log in with the old password
         self.attempt_wrong_password_login("kermit", old_password)
 
-    def test_cant_reset_password_without_clicking_link(self):
+    def test_cant_reset_password_without_clicking_link(self) -> None:
         """Test that we do actually need to click the link in the email"""
         old_password = "monkey"
         new_password = "kangeroo"
@@ -241,7 +250,7 @@ def test_cant_reset_password_without_clicking_link(self):
         # Assert we can't log in with the new password
         self.attempt_wrong_password_login("kermit", new_password)
 
-    def test_no_valid_token(self):
+    def test_no_valid_token(self) -> None:
         """Test that we do actually need to request a token and can't just
         make a session up.
         """
@@ -277,7 +286,7 @@ def test_no_valid_token(self):
         self.attempt_wrong_password_login("kermit", new_password)
 
     @unittest.override_config({"request_token_inhibit_3pid_errors": True})
-    def test_password_reset_bad_email_inhibit_error(self):
+    def test_password_reset_bad_email_inhibit_error(self) -> None:
         """Test that triggering a password reset with an email address that isn't bound
         to an account doesn't leak the lack of binding for that address if configured
         that way.
@@ -292,7 +301,12 @@ def test_password_reset_bad_email_inhibit_error(self):
 
         self.assertIsNotNone(session_id)
 
-    def _request_token(self, email, client_secret, ip="127.0.0.1"):
+    def _request_token(
+        self,
+        email: str,
+        client_secret: str,
+        ip: str = "127.0.0.1",
+    ) -> str:
         channel = self.make_request(
             "POST",
             b"account/password/email/requestToken",
@@ -309,7 +323,7 @@ def _request_token(self, email, client_secret, ip="127.0.0.1"):
 
         return channel.json_body["sid"]
 
-    def _validate_token(self, link):
+    def _validate_token(self, link: str) -> None:
         # Remove the host
         path = link.replace("https://example.com", "")
 
@@ -339,7 +353,7 @@ def _validate_token(self, link):
         )
         self.assertEqual(200, channel.code, channel.result)
 
-    def _get_link_from_email(self):
+    def _get_link_from_email(self) -> str:
         assert self.email_attempts, "No emails have been sent"
 
         raw_msg = self.email_attempts[-1].decode("UTF-8")
@@ -354,14 +368,19 @@ def _get_link_from_email(self):
         if not text:
             self.fail("Could not find text portion of email to parse")
 
+        assert text is not None
         match = re.search(r"https://example.com\S+", text)
         assert match, "Could not find link in email"
 
         return match.group(0)
 
     def _reset_password(
-        self, new_password, session_id, client_secret, expected_code=200
-    ):
+        self,
+        new_password: str,
+        session_id: str,
+        client_secret: str,
+        expected_code: int = 200,
+    ) -> None:
         channel = self.make_request(
             "POST",
             b"account/password",
@@ -388,11 +407,11 @@ class DeactivateTestCase(unittest.HomeserverTestCase):
         room.register_servlets,
     ]
 
-    def make_homeserver(self, reactor, clock):
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
         self.hs = self.setup_test_homeserver()
         return self.hs
 
-    def test_deactivate_account(self):
+    def test_deactivate_account(self) -> None:
         user_id = self.register_user("kermit", "test")
         tok = self.login("kermit", "test")
 
@@ -407,7 +426,7 @@ def test_deactivate_account(self):
         channel = self.make_request("GET", "account/whoami", access_token=tok)
         self.assertEqual(channel.code, 401)
 
-    def test_pending_invites(self):
+    def test_pending_invites(self) -> None:
         """Tests that deactivating a user rejects every pending invite for them."""
         store = self.hs.get_datastores().main
 
@@ -448,7 +467,7 @@ def test_pending_invites(self):
         self.assertEqual(len(memberships), 1, memberships)
         self.assertEqual(memberships[0].room_id, room_id, memberships)
 
-    def deactivate(self, user_id, tok):
+    def deactivate(self, user_id: str, tok: str) -> None:
         request_data = json.dumps(
             {
                 "auth": {
@@ -474,12 +493,12 @@ class WhoamiTestCase(unittest.HomeserverTestCase):
         register.register_servlets,
     ]
 
-    def default_config(self):
+    def default_config(self) -> Dict[str, Any]:
         config = super().default_config()
         config["allow_guest_access"] = True
         return config
 
-    def test_GET_whoami(self):
+    def test_GET_whoami(self) -> None:
         device_id = "wouldgohere"
         user_id = self.register_user("kermit", "test")
         tok = self.login("kermit", "test", device_id=device_id)
@@ -496,7 +515,7 @@ def test_GET_whoami(self):
             },
         )
 
-    def test_GET_whoami_guests(self):
+    def test_GET_whoami_guests(self) -> None:
         channel = self.make_request(
             b"POST", b"/_matrix/client/r0/register?kind=guest", b"{}"
         )
@@ -516,7 +535,7 @@ def test_GET_whoami_guests(self):
             },
         )
 
-    def test_GET_whoami_appservices(self):
+    def test_GET_whoami_appservices(self) -> None:
         user_id = "@as:test"
         as_token = "i_am_an_app_service"
 
@@ -541,7 +560,7 @@ def test_GET_whoami_appservices(self):
         )
         self.assertFalse(hasattr(whoami, "device_id"))
 
-    def _whoami(self, tok):
+    def _whoami(self, tok: str) -> JsonDict:
         channel = self.make_request("GET", "account/whoami", {}, access_token=tok)
         self.assertEqual(channel.code, 200)
         return channel.json_body
@@ -555,7 +574,7 @@ class ThreepidEmailRestTestCase(unittest.HomeserverTestCase):
         synapse.rest.admin.register_servlets_for_client_rest_resource,
     ]
 
-    def make_homeserver(self, reactor, clock):
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
         config = self.default_config()
 
         # Email config.
@@ -576,16 +595,23 @@ def make_homeserver(self, reactor, clock):
         self.hs = self.setup_test_homeserver(config=config)
 
         async def sendmail(
-            reactor, smtphost, smtpport, from_addr, to_addrs, msg, **kwargs
-        ):
-            self.email_attempts.append(msg)
-
-        self.email_attempts = []
+            reactor: IReactorTCP,
+            smtphost: str,
+            smtpport: int,
+            from_addr: str,
+            to_addr: str,
+            msg_bytes: bytes,
+            *args: Any,
+            **kwargs: Any,
+        ) -> None:
+            self.email_attempts.append(msg_bytes)
+
+        self.email_attempts: List[bytes] = []
         self.hs.get_send_email_handler()._sendmail = sendmail
 
         return self.hs
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.store = hs.get_datastores().main
 
         self.user_id = self.register_user("kermit", "test")
@@ -593,83 +619,73 @@ def prepare(self, reactor, clock, hs):
         self.email = "test@example.com"
         self.url_3pid = b"account/3pid"
 
-    def test_add_valid_email(self):
-        self.get_success(self._add_email(self.email, self.email))
+    def test_add_valid_email(self) -> None:
+        self._add_email(self.email, self.email)
 
-    def test_add_valid_email_second_time(self):
-        self.get_success(self._add_email(self.email, self.email))
-        self.get_success(
-            self._request_token_invalid_email(
-                self.email,
-                expected_errcode=Codes.THREEPID_IN_USE,
-                expected_error="Email is already in use",
-            )
+    def test_add_valid_email_second_time(self) -> None:
+        self._add_email(self.email, self.email)
+        self._request_token_invalid_email(
+            self.email,
+            expected_errcode=Codes.THREEPID_IN_USE,
+            expected_error="Email is already in use",
         )
 
-    def test_add_valid_email_second_time_canonicalise(self):
-        self.get_success(self._add_email(self.email, self.email))
-        self.get_success(
-            self._request_token_invalid_email(
-                "TEST@EXAMPLE.COM",
-                expected_errcode=Codes.THREEPID_IN_USE,
-                expected_error="Email is already in use",
-            )
+    def test_add_valid_email_second_time_canonicalise(self) -> None:
+        self._add_email(self.email, self.email)
+        self._request_token_invalid_email(
+            "TEST@EXAMPLE.COM",
+            expected_errcode=Codes.THREEPID_IN_USE,
+            expected_error="Email is already in use",
         )
 
-    def test_add_email_no_at(self):
-        self.get_success(
-            self._request_token_invalid_email(
-                "address-without-at.bar",
-                expected_errcode=Codes.UNKNOWN,
-                expected_error="Unable to parse email address",
-            )
+    def test_add_email_no_at(self) -> None:
+        self._request_token_invalid_email(
+            "address-without-at.bar",
+            expected_errcode=Codes.UNKNOWN,
+            expected_error="Unable to parse email address",
         )
 
-    def test_add_email_two_at(self):
-        self.get_success(
-            self._request_token_invalid_email(
-                "foo@foo@test.bar",
-                expected_errcode=Codes.UNKNOWN,
-                expected_error="Unable to parse email address",
-            )
+    def test_add_email_two_at(self) -> None:
+        self._request_token_invalid_email(
+            "foo@foo@test.bar",
+            expected_errcode=Codes.UNKNOWN,
+            expected_error="Unable to parse email address",
         )
 
-    def test_add_email_bad_format(self):
-        self.get_success(
-            self._request_token_invalid_email(
-                "user@bad.example.net@good.example.com",
-                expected_errcode=Codes.UNKNOWN,
-                expected_error="Unable to parse email address",
-            )
+    def test_add_email_bad_format(self) -> None:
+        self._request_token_invalid_email(
+            "user@bad.example.net@good.example.com",
+            expected_errcode=Codes.UNKNOWN,
+            expected_error="Unable to parse email address",
         )
 
-    def test_add_email_domain_to_lower(self):
-        self.get_success(self._add_email("foo@TEST.BAR", "foo@test.bar"))
+    def test_add_email_domain_to_lower(self) -> None:
+        self._add_email("foo@TEST.BAR", "foo@test.bar")
 
-    def test_add_email_domain_with_umlaut(self):
-        self.get_success(self._add_email("foo@Öumlaut.com", "foo@öumlaut.com"))
+    def test_add_email_domain_with_umlaut(self) -> None:
+        self._add_email("foo@Öumlaut.com", "foo@öumlaut.com")
 
-    def test_add_email_address_casefold(self):
-        self.get_success(self._add_email("Strauß@Example.com", "strauss@example.com"))
+    def test_add_email_address_casefold(self) -> None:
+        self._add_email("Strauß@Example.com", "strauss@example.com")
 
-    def test_address_trim(self):
-        self.get_success(self._add_email(" foo@test.bar ", "foo@test.bar"))
+    def test_address_trim(self) -> None:
+        self._add_email(" foo@test.bar ", "foo@test.bar")
 
     @override_config({"rc_3pid_validation": {"burst_count": 3}})
-    def test_ratelimit_by_ip(self):
+    def test_ratelimit_by_ip(self) -> None:
         """Tests that adding emails is ratelimited by IP"""
 
         # We expect to be able to set three emails before getting ratelimited.
-        self.get_success(self._add_email("foo1@test.bar", "foo1@test.bar"))
-        self.get_success(self._add_email("foo2@test.bar", "foo2@test.bar"))
-        self.get_success(self._add_email("foo3@test.bar", "foo3@test.bar"))
+        self._add_email("foo1@test.bar", "foo1@test.bar")
+        self._add_email("foo2@test.bar", "foo2@test.bar")
+        self._add_email("foo3@test.bar", "foo3@test.bar")
 
         with self.assertRaises(HttpResponseException) as cm:
-            self.get_success(self._add_email("foo4@test.bar", "foo4@test.bar"))
+            self._add_email("foo4@test.bar", "foo4@test.bar")
 
         self.assertEqual(cm.exception.code, 429)
 
-    def test_add_email_if_disabled(self):
+    def test_add_email_if_disabled(self) -> None:
         """Test adding email to profile when doing so is disallowed"""
         self.hs.config.registration.enable_3pid_changes = False
 
@@ -695,7 +711,7 @@ def test_add_email_if_disabled(self):
             },
             access_token=self.user_id_tok,
         )
-        self.assertEqual(400, int(channel.result["code"]), msg=channel.result["body"])
+        self.assertEqual(400, channel.code, msg=channel.result["body"])
         self.assertEqual(Codes.FORBIDDEN, channel.json_body["errcode"])
 
         # Get user
@@ -705,10 +721,10 @@ def test_add_email_if_disabled(self):
             access_token=self.user_id_tok,
         )
 
-        self.assertEqual(200, int(channel.result["code"]), msg=channel.result["body"])
+        self.assertEqual(200, channel.code, msg=channel.result["body"])
         self.assertFalse(channel.json_body["threepids"])
 
-    def test_delete_email(self):
+    def test_delete_email(self) -> None:
         """Test deleting an email from profile"""
         # Add a threepid
         self.get_success(
@@ -727,7 +743,7 @@ def test_delete_email(self):
             {"medium": "email", "address": self.email},
             access_token=self.user_id_tok,
         )
-        self.assertEqual(200, int(channel.result["code"]), msg=channel.result["body"])
+        self.assertEqual(200, channel.code, msg=channel.result["body"])
 
         # Get user
         channel = self.make_request(
@@ -736,10 +752,10 @@ def test_delete_email(self):
             access_token=self.user_id_tok,
         )
 
-        self.assertEqual(200, int(channel.result["code"]), msg=channel.result["body"])
+        self.assertEqual(200, channel.code, msg=channel.result["body"])
         self.assertFalse(channel.json_body["threepids"])
 
-    def test_delete_email_if_disabled(self):
+    def test_delete_email_if_disabled(self) -> None:
         """Test deleting an email from profile when disallowed"""
         self.hs.config.registration.enable_3pid_changes = False
 
@@ -761,7 +777,7 @@ def test_delete_email_if_disabled(self):
             access_token=self.user_id_tok,
         )
 
-        self.assertEqual(400, int(channel.result["code"]), msg=channel.result["body"])
+        self.assertEqual(400, channel.code, msg=channel.result["body"])
         self.assertEqual(Codes.FORBIDDEN, channel.json_body["errcode"])
 
         # Get user
@@ -771,11 +787,11 @@ def test_delete_email_if_disabled(self):
             access_token=self.user_id_tok,
         )
 
-        self.assertEqual(200, int(channel.result["code"]), msg=channel.result["body"])
+        self.assertEqual(200, channel.code, msg=channel.result["body"])
         self.assertEqual("email", channel.json_body["threepids"][0]["medium"])
         self.assertEqual(self.email, channel.json_body["threepids"][0]["address"])
 
-    def test_cant_add_email_without_clicking_link(self):
+    def test_cant_add_email_without_clicking_link(self) -> None:
         """Test that we do actually need to click the link in the email"""
         client_secret = "foobar"
         session_id = self._request_token(self.email, client_secret)
@@ -797,7 +813,7 @@ def test_cant_add_email_without_clicking_link(self):
             },
             access_token=self.user_id_tok,
         )
-        self.assertEqual(400, int(channel.result["code"]), msg=channel.result["body"])
+        self.assertEqual(400, channel.code, msg=channel.result["body"])
         self.assertEqual(Codes.THREEPID_AUTH_FAILED, channel.json_body["errcode"])
 
         # Get user
@@ -807,10 +823,10 @@ def test_cant_add_email_without_clicking_link(self):
             access_token=self.user_id_tok,
         )
 
-        self.assertEqual(200, int(channel.result["code"]), msg=channel.result["body"])
+        self.assertEqual(200, channel.code, msg=channel.result["body"])
         self.assertFalse(channel.json_body["threepids"])
 
-    def test_no_valid_token(self):
+    def test_no_valid_token(self) -> None:
         """Test that we do actually need to request a token and can't just
         make a session up.
         """
@@ -832,7 +848,7 @@ def test_no_valid_token(self):
             },
             access_token=self.user_id_tok,
         )
-        self.assertEqual(400, int(channel.result["code"]), msg=channel.result["body"])
+        self.assertEqual(400, channel.code, msg=channel.result["body"])
         self.assertEqual(Codes.THREEPID_AUTH_FAILED, channel.json_body["errcode"])
 
         # Get user
@@ -842,11 +858,11 @@ def test_no_valid_token(self):
             access_token=self.user_id_tok,
         )
 
-        self.assertEqual(200, int(channel.result["code"]), msg=channel.result["body"])
+        self.assertEqual(200, channel.code, msg=channel.result["body"])
         self.assertFalse(channel.json_body["threepids"])
 
     @override_config({"next_link_domain_whitelist": None})
-    def test_next_link(self):
+    def test_next_link(self) -> None:
         """Tests a valid next_link parameter value with no whitelist (good case)"""
         self._request_token(
             "something@example.com",
@@ -856,7 +872,7 @@ def test_next_link(self):
         )
 
     @override_config({"next_link_domain_whitelist": None})
-    def test_next_link_exotic_protocol(self):
+    def test_next_link_exotic_protocol(self) -> None:
         """Tests using a esoteric protocol as a next_link parameter value.
         Someone may be hosting a client on IPFS etc.
         """
@@ -868,7 +884,7 @@ def test_next_link_exotic_protocol(self):
         )
 
     @override_config({"next_link_domain_whitelist": None})
-    def test_next_link_file_uri(self):
+    def test_next_link_file_uri(self) -> None:
         """Tests next_link parameters cannot be file URI"""
         # Attempt to use a next_link value that points to the local disk
         self._request_token(
@@ -879,7 +895,7 @@ def test_next_link_file_uri(self):
         )
 
     @override_config({"next_link_domain_whitelist": ["example.com", "example.org"]})
-    def test_next_link_domain_whitelist(self):
+    def test_next_link_domain_whitelist(self) -> None:
         """Tests next_link parameters must fit the whitelist if provided"""
 
         # Ensure not providing a next_link parameter still works
@@ -912,7 +928,7 @@ def test_next_link_domain_whitelist(self):
         )
 
     @override_config({"next_link_domain_whitelist": []})
-    def test_empty_next_link_domain_whitelist(self):
+    def test_empty_next_link_domain_whitelist(self) -> None:
         """Tests an empty next_lint_domain_whitelist value, meaning next_link is essentially
         disallowed
         """
@@ -962,28 +978,28 @@ def _request_token(
 
     def _request_token_invalid_email(
         self,
-        email,
-        expected_errcode,
-        expected_error,
-        client_secret="foobar",
-    ):
+        email: str,
+        expected_errcode: str,
+        expected_error: str,
+        client_secret: str = "foobar",
+    ) -> None:
         channel = self.make_request(
             "POST",
             b"account/3pid/email/requestToken",
             {"client_secret": client_secret, "email": email, "send_attempt": 1},
         )
-        self.assertEqual(400, int(channel.result["code"]), msg=channel.result["body"])
+        self.assertEqual(400, channel.code, msg=channel.result["body"])
         self.assertEqual(expected_errcode, channel.json_body["errcode"])
         self.assertEqual(expected_error, channel.json_body["error"])
 
-    def _validate_token(self, link):
+    def _validate_token(self, link: str) -> None:
         # Remove the host
         path = link.replace("https://example.com", "")
 
         channel = self.make_request("GET", path, shorthand=False)
         self.assertEqual(200, channel.code, channel.result)
 
-    def _get_link_from_email(self):
+    def _get_link_from_email(self) -> str:
         assert self.email_attempts, "No emails have been sent"
 
         raw_msg = self.email_attempts[-1].decode("UTF-8")
@@ -998,12 +1014,13 @@ def _get_link_from_email(self):
         if not text:
             self.fail("Could not find text portion of email to parse")
 
+        assert text is not None
         match = re.search(r"https://example.com\S+", text)
         assert match, "Could not find link in email"
 
         return match.group(0)
 
-    def _add_email(self, request_email, expected_email):
+    def _add_email(self, request_email: str, expected_email: str) -> None:
         """Test adding an email to profile"""
         previous_email_attempts = len(self.email_attempts)
 
@@ -1030,7 +1047,7 @@ def _add_email(self, request_email, expected_email):
             access_token=self.user_id_tok,
         )
 
-        self.assertEqual(200, int(channel.result["code"]), msg=channel.result["body"])
+        self.assertEqual(200, channel.code, msg=channel.result["body"])
 
         # Get user
         channel = self.make_request(
@@ -1039,7 +1056,7 @@ def _add_email(self, request_email, expected_email):
             access_token=self.user_id_tok,
         )
 
-        self.assertEqual(200, int(channel.result["code"]), msg=channel.result["body"])
+        self.assertEqual(200, channel.code, msg=channel.result["body"])
         self.assertEqual("email", channel.json_body["threepids"][0]["medium"])
 
         threepids = {threepid["address"] for threepid in channel.json_body["threepids"]}
@@ -1055,18 +1072,18 @@ class AccountStatusTestCase(unittest.HomeserverTestCase):
 
     url = "/_matrix/client/unstable/org.matrix.msc3720/account_status"
 
-    def make_homeserver(self, reactor, clock):
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
         config = self.default_config()
         config["experimental_features"] = {"msc3720_enabled": True}
 
         return self.setup_test_homeserver(config=config)
 
-    def prepare(self, reactor: MemoryReactor, clock: Clock, homeserver: HomeServer):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.requester = self.register_user("requester", "password")
         self.requester_tok = self.login("requester", "password")
-        self.server_name = homeserver.config.server.server_name
+        self.server_name = hs.config.server.server_name
 
-    def test_missing_mxid(self):
+    def test_missing_mxid(self) -> None:
         """Tests that not providing any MXID raises an error."""
         self._test_status(
             users=None,
@@ -1074,7 +1091,7 @@ def test_missing_mxid(self):
             expected_errcode=Codes.MISSING_PARAM,
         )
 
-    def test_invalid_mxid(self):
+    def test_invalid_mxid(self) -> None:
         """Tests that providing an invalid MXID raises an error."""
         self._test_status(
             users=["bad:test"],
@@ -1082,7 +1099,7 @@ def test_invalid_mxid(self):
             expected_errcode=Codes.INVALID_PARAM,
         )
 
-    def test_local_user_not_exists(self):
+    def test_local_user_not_exists(self) -> None:
         """Tests that the account status endpoints correctly reports that a user doesn't
         exist.
         """
@@ -1098,7 +1115,7 @@ def test_local_user_not_exists(self):
             expected_failures=[],
         )
 
-    def test_local_user_exists(self):
+    def test_local_user_exists(self) -> None:
         """Tests that the account status endpoint correctly reports that a user doesn't
         exist.
         """
@@ -1115,7 +1132,7 @@ def test_local_user_exists(self):
             expected_failures=[],
         )
 
-    def test_local_user_deactivated(self):
+    def test_local_user_deactivated(self) -> None:
         """Tests that the account status endpoint correctly reports a deactivated user."""
         user = self.register_user("someuser", "password")
         self.get_success(
@@ -1135,7 +1152,7 @@ def test_local_user_deactivated(self):
             expected_failures=[],
         )
 
-    def test_mixed_local_and_remote_users(self):
+    def test_mixed_local_and_remote_users(self) -> None:
         """Tests that if some users are remote the account status endpoint correctly
         merges the remote responses with the local result.
         """
@@ -1150,7 +1167,13 @@ def test_mixed_local_and_remote_users(self):
             "@bad:badremote",
         ]
 
-        async def post_json(destination, path, data, *a, **kwa):
+        async def post_json(
+            destination: str,
+            path: str,
+            data: Optional[JsonDict] = None,
+            *a: Any,
+            **kwa: Any,
+        ) -> Union[JsonDict, list]:
             if destination == "remote":
                 return {
                     "account_statuses": {
@@ -1160,9 +1183,7 @@ async def post_json(destination, path, data, *a, **kwa):
                         },
                     }
                 }
-            if destination == "otherremote":
-                return {}
-            if destination == "badremote":
+            elif destination == "badremote":
                 # badremote tries to overwrite the status of a user that doesn't belong
                 # to it (i.e. users[1]) with false data, which Synapse is expected to
                 # ignore.
@@ -1176,6 +1197,9 @@ async def post_json(destination, path, data, *a, **kwa):
                         },
                     }
                 }
+            # if destination == "otherremote"
+            else:
+                return {}
 
         # Register a mock that will return the expected result depending on the remote.
         self.hs.get_federation_http_client().post_json = Mock(side_effect=post_json)
@@ -1205,7 +1229,7 @@ def _test_status(
         expected_statuses: Optional[Dict[str, Dict[str, bool]]] = None,
         expected_failures: Optional[List[str]] = None,
         expected_errcode: Optional[str] = None,
-    ):
+    ) -> None:
         """Send a request to the account status endpoint and check that the response
         matches with what's expected.
 
diff --git a/tests/rest/client/test_filter.py b/tests/rest/client/test_filter.py
index 5c31a54421df..823e8ab8c474 100644
--- a/tests/rest/client/test_filter.py
+++ b/tests/rest/client/test_filter.py
@@ -12,10 +12,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from twisted.internet import defer
+from twisted.test.proto_helpers import MemoryReactor
 
 from synapse.api.errors import Codes
 from synapse.rest.client import filter
+from synapse.server import HomeServer
+from synapse.util import Clock
 
 from tests import unittest
 
@@ -30,11 +32,11 @@ class FilterTestCase(unittest.HomeserverTestCase):
     EXAMPLE_FILTER_JSON = b'{"room": {"timeline": {"types": ["m.room.message"]}}}'
     servlets = [filter.register_servlets]
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.filtering = hs.get_filtering()
         self.store = hs.get_datastores().main
 
-    def test_add_filter(self):
+    def test_add_filter(self) -> None:
         channel = self.make_request(
             "POST",
             "/_matrix/client/r0/user/%s/filter" % (self.user_id),
@@ -43,11 +45,13 @@ def test_add_filter(self):
 
         self.assertEqual(channel.result["code"], b"200")
         self.assertEqual(channel.json_body, {"filter_id": "0"})
-        filter = self.store.get_user_filter(user_localpart="apple", filter_id=0)
+        filter = self.get_success(
+            self.store.get_user_filter(user_localpart="apple", filter_id=0)
+        )
         self.pump()
-        self.assertEqual(filter.result, self.EXAMPLE_FILTER)
+        self.assertEqual(filter, self.EXAMPLE_FILTER)
 
-    def test_add_filter_for_other_user(self):
+    def test_add_filter_for_other_user(self) -> None:
         channel = self.make_request(
             "POST",
             "/_matrix/client/r0/user/%s/filter" % ("@watermelon:test"),
@@ -57,7 +61,7 @@ def test_add_filter_for_other_user(self):
         self.assertEqual(channel.result["code"], b"403")
         self.assertEqual(channel.json_body["errcode"], Codes.FORBIDDEN)
 
-    def test_add_filter_non_local_user(self):
+    def test_add_filter_non_local_user(self) -> None:
         _is_mine = self.hs.is_mine
         self.hs.is_mine = lambda target_user: False
         channel = self.make_request(
@@ -70,14 +74,13 @@ def test_add_filter_non_local_user(self):
         self.assertEqual(channel.result["code"], b"403")
         self.assertEqual(channel.json_body["errcode"], Codes.FORBIDDEN)
 
-    def test_get_filter(self):
-        filter_id = defer.ensureDeferred(
+    def test_get_filter(self) -> None:
+        filter_id = self.get_success(
             self.filtering.add_user_filter(
                 user_localpart="apple", user_filter=self.EXAMPLE_FILTER
             )
         )
         self.reactor.advance(1)
-        filter_id = filter_id.result
         channel = self.make_request(
             "GET", "/_matrix/client/r0/user/%s/filter/%s" % (self.user_id, filter_id)
         )
@@ -85,7 +88,7 @@ def test_get_filter(self):
         self.assertEqual(channel.result["code"], b"200")
         self.assertEqual(channel.json_body, self.EXAMPLE_FILTER)
 
-    def test_get_filter_non_existant(self):
+    def test_get_filter_non_existant(self) -> None:
         channel = self.make_request(
             "GET", "/_matrix/client/r0/user/%s/filter/12382148321" % (self.user_id)
         )
@@ -95,7 +98,7 @@ def test_get_filter_non_existant(self):
 
     # Currently invalid params do not have an appropriate errcode
     # in errors.py
-    def test_get_filter_invalid_id(self):
+    def test_get_filter_invalid_id(self) -> None:
         channel = self.make_request(
             "GET", "/_matrix/client/r0/user/%s/filter/foobar" % (self.user_id)
         )
@@ -103,7 +106,7 @@ def test_get_filter_invalid_id(self):
         self.assertEqual(channel.result["code"], b"400")
 
     # No ID also returns an invalid_id error
-    def test_get_filter_no_id(self):
+    def test_get_filter_no_id(self) -> None:
         channel = self.make_request(
             "GET", "/_matrix/client/r0/user/%s/filter/" % (self.user_id)
         )
diff --git a/tests/rest/client/test_relations.py b/tests/rest/client/test_relations.py
index c8db45719e07..171f4e97c8fd 100644
--- a/tests/rest/client/test_relations.py
+++ b/tests/rest/client/test_relations.py
@@ -15,7 +15,7 @@
 
 import itertools
 import urllib.parse
-from typing import Dict, List, Optional, Tuple
+from typing import Any, Dict, List, Optional, Tuple
 from unittest.mock import patch
 
 from twisted.test.proto_helpers import MemoryReactor
@@ -24,8 +24,7 @@
 from synapse.rest import admin
 from synapse.rest.client import login, register, relations, room, sync
 from synapse.server import HomeServer
-from synapse.storage.relations import RelationPaginationToken
-from synapse.types import JsonDict, StreamToken
+from synapse.types import JsonDict
 from synapse.util import Clock
 
 from tests import unittest
@@ -34,7 +33,7 @@
 from tests.test_utils.event_injection import inject_event
 
 
-class RelationsTestCase(unittest.HomeserverTestCase):
+class BaseRelationsTestCase(unittest.HomeserverTestCase):
     servlets = [
         relations.register_servlets,
         room.register_servlets,
@@ -45,10 +44,9 @@ class RelationsTestCase(unittest.HomeserverTestCase):
     ]
     hijack_auth = False
 
-    def default_config(self) -> dict:
+    def default_config(self) -> Dict[str, Any]:
         # We need to enable msc1849 support for aggregations
         config = super().default_config()
-        config["experimental_msc1849_support_enabled"] = True
 
         # We enable frozen dicts as relations/edits change event contents, so we
         # want to test that we don't modify the events in the caches.
@@ -67,10 +65,62 @@ def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         res = self.helper.send(self.room, body="Hi!", tok=self.user_token)
         self.parent_id = res["event_id"]
 
-    def test_send_relation(self) -> None:
-        """Tests that sending a relation using the new /send_relation works
-        creates the right shape of event.
+    def _create_user(self, localpart: str) -> Tuple[str, str]:
+        user_id = self.register_user(localpart, "abc123")
+        access_token = self.login(localpart, "abc123")
+
+        return user_id, access_token
+
+    def _send_relation(
+        self,
+        relation_type: str,
+        event_type: str,
+        key: Optional[str] = None,
+        content: Optional[dict] = None,
+        access_token: Optional[str] = None,
+        parent_id: Optional[str] = None,
+    ) -> FakeChannel:
+        """Helper function to send a relation pointing at `self.parent_id`
+
+        Args:
+            relation_type: One of `RelationTypes`
+            event_type: The type of the event to create
+            key: The aggregation key used for m.annotation relation type.
+            content: The content of the created event. Will be modified to configure
+                the m.relates_to key based on the other provided parameters.
+            access_token: The access token used to send the relation, defaults
+                to `self.user_token`
+            parent_id: The event_id this relation relates to. If None, then self.parent_id
+
+        Returns:
+            FakeChannel
         """
+        if not access_token:
+            access_token = self.user_token
+
+        original_id = parent_id if parent_id else self.parent_id
+
+        if content is None:
+            content = {}
+        content["m.relates_to"] = {
+            "event_id": original_id,
+            "rel_type": relation_type,
+        }
+        if key is not None:
+            content["m.relates_to"]["key"] = key
+
+        channel = self.make_request(
+            "POST",
+            f"/_matrix/client/v3/rooms/{self.room}/send/{event_type}",
+            content,
+            access_token=access_token,
+        )
+        return channel
+
+
+class RelationsTestCase(BaseRelationsTestCase):
+    def test_send_relation(self) -> None:
+        """Tests that sending a relation works."""
 
         channel = self._send_relation(RelationTypes.ANNOTATION, "m.reaction", key="👍")
         self.assertEqual(200, channel.code, channel.json_body)
@@ -79,7 +129,7 @@ def test_send_relation(self) -> None:
 
         channel = self.make_request(
             "GET",
-            "/rooms/%s/event/%s" % (self.room, event_id),
+            f"/rooms/{self.room}/event/{event_id}",
             access_token=self.user_token,
         )
         self.assertEqual(200, channel.code, channel.json_body)
@@ -230,15 +280,6 @@ def test_basic_paginate_relations(self) -> None:
             channel.json_body["chunk"][0],
         )
 
-    def _stream_token_to_relation_token(self, token: str) -> str:
-        """Convert a StreamToken into a legacy token (RelationPaginationToken)."""
-        room_key = self.get_success(StreamToken.from_string(self.store, token)).room_key
-        return self.get_success(
-            RelationPaginationToken(
-                topological=room_key.topological, stream=room_key.stream
-            ).to_string(self.store)
-        )
-
     def test_repeated_paginate_relations(self) -> None:
         """Test that if we paginate using a limit and tokens then we get the
         expected events.
@@ -279,34 +320,6 @@ def test_repeated_paginate_relations(self) -> None:
         found_event_ids.reverse()
         self.assertEqual(found_event_ids, expected_event_ids)
 
-        # Reset and try again, but convert the tokens to the legacy format.
-        prev_token = ""
-        found_event_ids = []
-        for _ in range(20):
-            from_token = ""
-            if prev_token:
-                from_token = "&from=" + self._stream_token_to_relation_token(prev_token)
-
-            channel = self.make_request(
-                "GET",
-                f"/_matrix/client/unstable/rooms/{self.room}/relations/{self.parent_id}?limit=1{from_token}",
-                access_token=self.user_token,
-            )
-            self.assertEqual(200, channel.code, channel.json_body)
-
-            found_event_ids.extend(e["event_id"] for e in channel.json_body["chunk"])
-            next_batch = channel.json_body.get("next_batch")
-
-            self.assertNotEqual(prev_token, next_batch)
-            prev_token = next_batch
-
-            if not prev_token:
-                break
-
-        # We paginated backwards, so reverse
-        found_event_ids.reverse()
-        self.assertEqual(found_event_ids, expected_event_ids)
-
     def test_pagination_from_sync_and_messages(self) -> None:
         """Pagination tokens from /sync and /messages can be used to paginate /relations."""
         channel = self._send_relation(RelationTypes.ANNOTATION, "m.reaction", "A")
@@ -317,9 +330,7 @@ def test_pagination_from_sync_and_messages(self) -> None:
 
         # Request /sync, limiting it such that only the latest event is returned
         # (and not the relation).
-        filter = urllib.parse.quote_plus(
-            '{"room": {"timeline": {"limit": 1}}}'.encode()
-        )
+        filter = urllib.parse.quote_plus(b'{"room": {"timeline": {"limit": 1}}}')
         channel = self.make_request(
             "GET", f"/sync?filter={filter}", access_token=self.user_token
         )
@@ -404,8 +415,7 @@ def test_aggregation_pagination_groups(self) -> None:
 
             channel = self.make_request(
                 "GET",
-                "/_matrix/client/unstable/rooms/%s/aggregations/%s?limit=1%s"
-                % (self.room, self.parent_id, from_token),
+                f"/_matrix/client/unstable/rooms/{self.room}/aggregations/{self.parent_id}?limit=1{from_token}",
                 access_token=self.user_token,
             )
             self.assertEqual(200, channel.code, channel.json_body)
@@ -495,39 +505,6 @@ def test_aggregation_pagination_within_group(self) -> None:
         found_event_ids.reverse()
         self.assertEqual(found_event_ids, expected_event_ids)
 
-        # Reset and try again, but convert the tokens to the legacy format.
-        prev_token = ""
-        found_event_ids = []
-        for _ in range(20):
-            from_token = ""
-            if prev_token:
-                from_token = "&from=" + self._stream_token_to_relation_token(prev_token)
-
-            channel = self.make_request(
-                "GET",
-                f"/_matrix/client/unstable/rooms/{self.room}"
-                f"/aggregations/{self.parent_id}/{RelationTypes.ANNOTATION}"
-                f"/m.reaction/{encoded_key}?limit=1{from_token}",
-                access_token=self.user_token,
-            )
-            self.assertEqual(200, channel.code, channel.json_body)
-
-            self.assertEqual(len(channel.json_body["chunk"]), 1, channel.json_body)
-
-            found_event_ids.extend(e["event_id"] for e in channel.json_body["chunk"])
-
-            next_batch = channel.json_body.get("next_batch")
-
-            self.assertNotEqual(prev_token, next_batch)
-            prev_token = next_batch
-
-            if not prev_token:
-                break
-
-        # We paginated backwards, so reverse
-        found_event_ids.reverse()
-        self.assertEqual(found_event_ids, expected_event_ids)
-
     def test_aggregation(self) -> None:
         """Test that annotations get correctly aggregated."""
 
@@ -544,8 +521,7 @@ def test_aggregation(self) -> None:
 
         channel = self.make_request(
             "GET",
-            "/_matrix/client/unstable/rooms/%s/aggregations/%s"
-            % (self.room, self.parent_id),
+            f"/_matrix/client/unstable/rooms/{self.room}/aggregations/{self.parent_id}",
             access_token=self.user_token,
         )
         self.assertEqual(200, channel.code, channel.json_body)
@@ -560,54 +536,18 @@ def test_aggregation(self) -> None:
             },
         )
 
-    def test_aggregation_redactions(self) -> None:
-        """Test that annotations get correctly aggregated after a redaction."""
-
-        channel = self._send_relation(RelationTypes.ANNOTATION, "m.reaction", "a")
-        self.assertEqual(200, channel.code, channel.json_body)
-        to_redact_event_id = channel.json_body["event_id"]
-
-        channel = self._send_relation(
-            RelationTypes.ANNOTATION, "m.reaction", "a", access_token=self.user2_token
-        )
-        self.assertEqual(200, channel.code, channel.json_body)
-
-        # Now lets redact one of the 'a' reactions
-        channel = self.make_request(
-            "POST",
-            "/_matrix/client/r0/rooms/%s/redact/%s" % (self.room, to_redact_event_id),
-            access_token=self.user_token,
-            content={},
-        )
-        self.assertEqual(200, channel.code, channel.json_body)
-
-        channel = self.make_request(
-            "GET",
-            "/_matrix/client/unstable/rooms/%s/aggregations/%s"
-            % (self.room, self.parent_id),
-            access_token=self.user_token,
-        )
-        self.assertEqual(200, channel.code, channel.json_body)
-
-        self.assertEqual(
-            channel.json_body,
-            {"chunk": [{"type": "m.reaction", "key": "a", "count": 1}]},
-        )
-
     def test_aggregation_must_be_annotation(self) -> None:
         """Test that aggregations must be annotations."""
 
         channel = self.make_request(
             "GET",
-            "/_matrix/client/unstable/rooms/%s/aggregations/%s/%s?limit=1"
-            % (self.room, self.parent_id, RelationTypes.REPLACE),
+            f"/_matrix/client/unstable/rooms/{self.room}/aggregations"
+            f"/{self.parent_id}/{RelationTypes.REPLACE}?limit=1",
             access_token=self.user_token,
         )
         self.assertEqual(400, channel.code, channel.json_body)
 
-    @unittest.override_config(
-        {"experimental_features": {"msc3440_enabled": True, "msc3666_enabled": True}}
-    )
+    @unittest.override_config({"experimental_features": {"msc3666_enabled": True}})
     def test_bundled_aggregations(self) -> None:
         """
         Test that annotations, references, and threads get correctly bundled.
@@ -691,10 +631,8 @@ def assert_bundle(event_json: JsonDict) -> None:
                         }
                     },
                     "event_id": thread_2,
-                    "room_id": self.room,
                     "sender": self.user_id,
                     "type": "m.room.test",
-                    "user_id": self.user_id,
                 },
                 relations_dict[RelationTypes.THREAD].get("latest_event"),
             )
@@ -818,7 +756,6 @@ def test_aggregation_get_event_for_thread(self) -> None:
             },
         )
 
-    @unittest.override_config({"experimental_features": {"msc3440_enabled": True}})
     def test_ignore_invalid_room(self) -> None:
         """Test that we ignore invalid relations over federation."""
         # Create another room and send a message in it.
@@ -986,9 +923,7 @@ def assert_bundle(event_json: JsonDict) -> None:
 
         # Request sync, but limit the timeline so it becomes limited (and includes
         # bundled aggregations).
-        filter = urllib.parse.quote_plus(
-            '{"room": {"timeline": {"limit": 2}}}'.encode()
-        )
+        filter = urllib.parse.quote_plus(b'{"room": {"timeline": {"limit": 2}}}')
         channel = self.make_request(
             "GET", f"/sync?filter={filter}", access_token=self.user_token
         )
@@ -1053,7 +988,7 @@ def test_multi_edit(self) -> None:
 
         channel = self.make_request(
             "GET",
-            "/rooms/%s/event/%s" % (self.room, self.parent_id),
+            f"/rooms/{self.room}/event/{self.parent_id}",
             access_token=self.user_token,
         )
         self.assertEqual(200, channel.code, channel.json_body)
@@ -1096,7 +1031,7 @@ def test_edit_reply(self) -> None:
 
         channel = self.make_request(
             "GET",
-            "/rooms/%s/event/%s" % (self.room, reply),
+            f"/rooms/{self.room}/event/{reply}",
             access_token=self.user_token,
         )
         self.assertEqual(200, channel.code, channel.json_body)
@@ -1127,7 +1062,6 @@ def test_edit_reply(self) -> None:
             {"event_id": edit_event_id, "sender": self.user_id}, m_replace_dict
         )
 
-    @unittest.override_config({"experimental_features": {"msc3440_enabled": True}})
     def test_edit_thread(self) -> None:
         """Test that editing a thread works."""
 
@@ -1198,7 +1132,7 @@ def test_edit_edit(self) -> None:
         # Request the original event.
         channel = self.make_request(
             "GET",
-            "/rooms/%s/event/%s" % (self.room, self.parent_id),
+            f"/rooms/{self.room}/event/{self.parent_id}",
             access_token=self.user_token,
         )
         self.assertEqual(200, channel.code, channel.json_body)
@@ -1217,102 +1151,6 @@ def test_edit_edit(self) -> None:
             {"event_id": edit_event_id, "sender": self.user_id}, m_replace_dict
         )
 
-    def test_relations_redaction_redacts_edits(self) -> None:
-        """Test that edits of an event are redacted when the original event
-        is redacted.
-        """
-        # Send a new event
-        res = self.helper.send(self.room, body="Heyo!", tok=self.user_token)
-        original_event_id = res["event_id"]
-
-        # Add a relation
-        channel = self._send_relation(
-            RelationTypes.REPLACE,
-            "m.room.message",
-            parent_id=original_event_id,
-            content={
-                "msgtype": "m.text",
-                "body": "Wibble",
-                "m.new_content": {"msgtype": "m.text", "body": "First edit"},
-            },
-        )
-        self.assertEqual(200, channel.code, channel.json_body)
-
-        # Check the relation is returned
-        channel = self.make_request(
-            "GET",
-            "/_matrix/client/unstable/rooms/%s/relations/%s/m.replace/m.room.message"
-            % (self.room, original_event_id),
-            access_token=self.user_token,
-        )
-        self.assertEqual(200, channel.code, channel.json_body)
-
-        self.assertIn("chunk", channel.json_body)
-        self.assertEqual(len(channel.json_body["chunk"]), 1)
-
-        # Redact the original event
-        channel = self.make_request(
-            "PUT",
-            "/rooms/%s/redact/%s/%s"
-            % (self.room, original_event_id, "test_relations_redaction_redacts_edits"),
-            access_token=self.user_token,
-            content="{}",
-        )
-        self.assertEqual(200, channel.code, channel.json_body)
-
-        # Try to check for remaining m.replace relations
-        channel = self.make_request(
-            "GET",
-            "/_matrix/client/unstable/rooms/%s/relations/%s/m.replace/m.room.message"
-            % (self.room, original_event_id),
-            access_token=self.user_token,
-        )
-        self.assertEqual(200, channel.code, channel.json_body)
-
-        # Check that no relations are returned
-        self.assertIn("chunk", channel.json_body)
-        self.assertEqual(channel.json_body["chunk"], [])
-
-    def test_aggregations_redaction_prevents_access_to_aggregations(self) -> None:
-        """Test that annotations of an event are redacted when the original event
-        is redacted.
-        """
-        # Send a new event
-        res = self.helper.send(self.room, body="Hello!", tok=self.user_token)
-        original_event_id = res["event_id"]
-
-        # Add a relation
-        channel = self._send_relation(
-            RelationTypes.ANNOTATION, "m.reaction", key="👍", parent_id=original_event_id
-        )
-        self.assertEqual(200, channel.code, channel.json_body)
-
-        # Redact the original
-        channel = self.make_request(
-            "PUT",
-            "/rooms/%s/redact/%s/%s"
-            % (
-                self.room,
-                original_event_id,
-                "test_aggregations_redaction_prevents_access_to_aggregations",
-            ),
-            access_token=self.user_token,
-            content="{}",
-        )
-        self.assertEqual(200, channel.code, channel.json_body)
-
-        # Check that aggregations returns zero
-        channel = self.make_request(
-            "GET",
-            "/_matrix/client/unstable/rooms/%s/aggregations/%s/m.annotation/m.reaction"
-            % (self.room, original_event_id),
-            access_token=self.user_token,
-        )
-        self.assertEqual(200, channel.code, channel.json_body)
-
-        self.assertIn("chunk", channel.json_body)
-        self.assertEqual(channel.json_body["chunk"], [])
-
     def test_unknown_relations(self) -> None:
         """Unknown relations should be accepted."""
         channel = self._send_relation("m.relation.test", "m.room.test")
@@ -1321,8 +1159,7 @@ def test_unknown_relations(self) -> None:
 
         channel = self.make_request(
             "GET",
-            "/_matrix/client/unstable/rooms/%s/relations/%s?limit=1"
-            % (self.room, self.parent_id),
+            f"/_matrix/client/unstable/rooms/{self.room}/relations/{self.parent_id}?limit=1",
             access_token=self.user_token,
         )
         self.assertEqual(200, channel.code, channel.json_body)
@@ -1343,7 +1180,7 @@ def test_unknown_relations(self) -> None:
         # When bundling the unknown relation is not included.
         channel = self.make_request(
             "GET",
-            "/rooms/%s/event/%s" % (self.room, self.parent_id),
+            f"/rooms/{self.room}/event/{self.parent_id}",
             access_token=self.user_token,
         )
         self.assertEqual(200, channel.code, channel.json_body)
@@ -1352,8 +1189,7 @@ def test_unknown_relations(self) -> None:
         # But unknown relations can be directly queried.
         channel = self.make_request(
             "GET",
-            "/_matrix/client/unstable/rooms/%s/aggregations/%s?limit=1"
-            % (self.room, self.parent_id),
+            f"/_matrix/client/unstable/rooms/{self.room}/aggregations/{self.parent_id}?limit=1",
             access_token=self.user_token,
         )
         self.assertEqual(200, channel.code, channel.json_body)
@@ -1369,58 +1205,6 @@ def _find_event_in_chunk(self, events: List[JsonDict]) -> JsonDict:
 
         raise AssertionError(f"Event {self.parent_id} not found in chunk")
 
-    def _send_relation(
-        self,
-        relation_type: str,
-        event_type: str,
-        key: Optional[str] = None,
-        content: Optional[dict] = None,
-        access_token: Optional[str] = None,
-        parent_id: Optional[str] = None,
-    ) -> FakeChannel:
-        """Helper function to send a relation pointing at `self.parent_id`
-
-        Args:
-            relation_type: One of `RelationTypes`
-            event_type: The type of the event to create
-            key: The aggregation key used for m.annotation relation type.
-            content: The content of the created event. Will be modified to configure
-                the m.relates_to key based on the other provided parameters.
-            access_token: The access token used to send the relation, defaults
-                to `self.user_token`
-            parent_id: The event_id this relation relates to. If None, then self.parent_id
-
-        Returns:
-            FakeChannel
-        """
-        if not access_token:
-            access_token = self.user_token
-
-        original_id = parent_id if parent_id else self.parent_id
-
-        if content is None:
-            content = {}
-        content["m.relates_to"] = {
-            "event_id": original_id,
-            "rel_type": relation_type,
-        }
-        if key is not None:
-            content["m.relates_to"]["key"] = key
-
-        channel = self.make_request(
-            "POST",
-            f"/_matrix/client/v3/rooms/{self.room}/send/{event_type}",
-            content,
-            access_token=access_token,
-        )
-        return channel
-
-    def _create_user(self, localpart: str) -> Tuple[str, str]:
-        user_id = self.register_user(localpart, "abc123")
-        access_token = self.login(localpart, "abc123")
-
-        return user_id, access_token
-
     def test_background_update(self) -> None:
         """Test the event_arbitrary_relations background update."""
         channel = self._send_relation(RelationTypes.ANNOTATION, "m.reaction", key="👍")
@@ -1482,3 +1266,297 @@ def test_background_update(self) -> None:
             [ev["event_id"] for ev in channel.json_body["chunk"]],
             [annotation_event_id_good, thread_event_id],
         )
+
+    def test_bundled_aggregations_with_filter(self) -> None:
+        """
+        If "unsigned" is an omitted field (due to filtering), adding the bundled
+        aggregations should not break.
+
+        Note that the spec allows for a server to return additional fields beyond
+        what is specified.
+        """
+        self._send_relation(RelationTypes.ANNOTATION, "m.reaction", "a")
+
+        # Note that the sync filter does not include "unsigned" as a field.
+        filter = urllib.parse.quote_plus(
+            b'{"event_fields": ["content", "event_id"], "room": {"timeline": {"limit": 3}}}'
+        )
+        channel = self.make_request(
+            "GET", f"/sync?filter={filter}", access_token=self.user_token
+        )
+        self.assertEqual(200, channel.code, channel.json_body)
+
+        # Ensure the timeline is limited, find the parent event.
+        room_timeline = channel.json_body["rooms"]["join"][self.room]["timeline"]
+        self.assertTrue(room_timeline["limited"])
+        parent_event = self._find_event_in_chunk(room_timeline["events"])
+
+        # Ensure there's bundled aggregations on it.
+        self.assertIn("unsigned", parent_event)
+        self.assertIn("m.relations", parent_event["unsigned"])
+
+
+class RelationRedactionTestCase(BaseRelationsTestCase):
+    """
+    Test the behaviour of relations when the parent or child event is redacted.
+
+    The behaviour of each relation type is subtly different which causes the tests
+    to be a bit repetitive, they follow a naming scheme of:
+
+        test_redact_(relation|parent)_{relation_type}
+
+    The first bit of "relation" means that the event with the relation defined
+    on it (the child event) is to be redacted. A "parent" means that the target
+    of the relation (the parent event) is to be redacted.
+
+    The relation_type describes which type of relation is under test (i.e. it is
+    related to the value of rel_type in the event content).
+    """
+
+    def _redact(self, event_id: str) -> None:
+        channel = self.make_request(
+            "POST",
+            f"/_matrix/client/r0/rooms/{self.room}/redact/{event_id}",
+            access_token=self.user_token,
+            content={},
+        )
+        self.assertEqual(200, channel.code, channel.json_body)
+
+    def _make_relation_requests(self) -> Tuple[List[str], JsonDict]:
+        """
+        Makes requests and ensures they result in a 200 response, returns a
+        tuple of results:
+
+        1. `/relations` -> Returns a list of event IDs.
+        2. `/event` -> Returns the response's m.relations field (from unsigned),
+            if it exists.
+        """
+
+        # Request the relations of the event.
+        channel = self.make_request(
+            "GET",
+            f"/_matrix/client/unstable/rooms/{self.room}/relations/{self.parent_id}",
+            access_token=self.user_token,
+        )
+        self.assertEquals(200, channel.code, channel.json_body)
+        event_ids = [ev["event_id"] for ev in channel.json_body["chunk"]]
+
+        # Fetch the bundled aggregations of the event.
+        channel = self.make_request(
+            "GET",
+            f"/_matrix/client/unstable/rooms/{self.room}/event/{self.parent_id}",
+            access_token=self.user_token,
+        )
+        self.assertEquals(200, channel.code, channel.json_body)
+        bundled_relations = channel.json_body["unsigned"].get("m.relations", {})
+
+        return event_ids, bundled_relations
+
+    def _get_aggregations(self) -> List[JsonDict]:
+        """Request /aggregations on the parent ID and includes the returned chunk."""
+        channel = self.make_request(
+            "GET",
+            f"/_matrix/client/unstable/rooms/{self.room}/aggregations/{self.parent_id}",
+            access_token=self.user_token,
+        )
+        self.assertEqual(200, channel.code, channel.json_body)
+        return channel.json_body["chunk"]
+
+    def test_redact_relation_annotation(self) -> None:
+        """
+        Test that annotations of an event are properly handled after the
+        annotation is redacted.
+
+        The redacted relation should not be included in bundled aggregations or
+        the response to relations.
+        """
+        channel = self._send_relation(RelationTypes.ANNOTATION, "m.reaction", "a")
+        self.assertEqual(200, channel.code, channel.json_body)
+        to_redact_event_id = channel.json_body["event_id"]
+
+        channel = self._send_relation(
+            RelationTypes.ANNOTATION, "m.reaction", "a", access_token=self.user2_token
+        )
+        self.assertEqual(200, channel.code, channel.json_body)
+        unredacted_event_id = channel.json_body["event_id"]
+
+        # Both relations should exist.
+        event_ids, relations = self._make_relation_requests()
+        self.assertCountEqual(event_ids, [to_redact_event_id, unredacted_event_id])
+        self.assertEquals(
+            relations["m.annotation"],
+            {"chunk": [{"type": "m.reaction", "key": "a", "count": 2}]},
+        )
+
+        # Both relations appear in the aggregation.
+        chunk = self._get_aggregations()
+        self.assertEqual(chunk, [{"type": "m.reaction", "key": "a", "count": 2}])
+
+        # Redact one of the reactions.
+        self._redact(to_redact_event_id)
+
+        # The unredacted relation should still exist.
+        event_ids, relations = self._make_relation_requests()
+        self.assertEquals(event_ids, [unredacted_event_id])
+        self.assertEquals(
+            relations["m.annotation"],
+            {"chunk": [{"type": "m.reaction", "key": "a", "count": 1}]},
+        )
+
+        # The unredacted aggregation should still exist.
+        chunk = self._get_aggregations()
+        self.assertEqual(chunk, [{"type": "m.reaction", "key": "a", "count": 1}])
+
+    def test_redact_relation_thread(self) -> None:
+        """
+        Test that thread replies are properly handled after the thread reply redacted.
+
+        The redacted event should not be included in bundled aggregations or
+        the response to relations.
+        """
+        channel = self._send_relation(
+            RelationTypes.THREAD,
+            EventTypes.Message,
+            content={"body": "reply 1", "msgtype": "m.text"},
+        )
+        self.assertEqual(200, channel.code, channel.json_body)
+        unredacted_event_id = channel.json_body["event_id"]
+
+        # Note that the *last* event in the thread is redacted, as that gets
+        # included in the bundled aggregation.
+        channel = self._send_relation(
+            RelationTypes.THREAD,
+            EventTypes.Message,
+            content={"body": "reply 2", "msgtype": "m.text"},
+        )
+        self.assertEqual(200, channel.code, channel.json_body)
+        to_redact_event_id = channel.json_body["event_id"]
+
+        # Both relations exist.
+        event_ids, relations = self._make_relation_requests()
+        self.assertEquals(event_ids, [to_redact_event_id, unredacted_event_id])
+        self.assertDictContainsSubset(
+            {
+                "count": 2,
+                "current_user_participated": True,
+            },
+            relations[RelationTypes.THREAD],
+        )
+        # And the latest event returned is the event that will be redacted.
+        self.assertEqual(
+            relations[RelationTypes.THREAD]["latest_event"]["event_id"],
+            to_redact_event_id,
+        )
+
+        # Redact one of the reactions.
+        self._redact(to_redact_event_id)
+
+        # The unredacted relation should still exist.
+        event_ids, relations = self._make_relation_requests()
+        self.assertEquals(event_ids, [unredacted_event_id])
+        self.assertDictContainsSubset(
+            {
+                "count": 1,
+                "current_user_participated": True,
+            },
+            relations[RelationTypes.THREAD],
+        )
+        # And the latest event is now the unredacted event.
+        self.assertEqual(
+            relations[RelationTypes.THREAD]["latest_event"]["event_id"],
+            unredacted_event_id,
+        )
+
+    def test_redact_parent_edit(self) -> None:
+        """Test that edits of an event are redacted when the original event
+        is redacted.
+        """
+        # Add a relation
+        channel = self._send_relation(
+            RelationTypes.REPLACE,
+            "m.room.message",
+            parent_id=self.parent_id,
+            content={
+                "msgtype": "m.text",
+                "body": "Wibble",
+                "m.new_content": {"msgtype": "m.text", "body": "First edit"},
+            },
+        )
+        self.assertEqual(200, channel.code, channel.json_body)
+
+        # Check the relation is returned
+        event_ids, relations = self._make_relation_requests()
+        self.assertEqual(len(event_ids), 1)
+        self.assertIn(RelationTypes.REPLACE, relations)
+
+        # Redact the original event
+        self._redact(self.parent_id)
+
+        # The relations are not returned.
+        event_ids, relations = self._make_relation_requests()
+        self.assertEqual(len(event_ids), 0)
+        self.assertEqual(relations, {})
+
+    def test_redact_parent_annotation(self) -> None:
+        """Test that annotations of an event are viewable when the original event
+        is redacted.
+        """
+        # Add a relation
+        channel = self._send_relation(RelationTypes.ANNOTATION, "m.reaction", key="👍")
+        self.assertEqual(200, channel.code, channel.json_body)
+        related_event_id = channel.json_body["event_id"]
+
+        # The relations should exist.
+        event_ids, relations = self._make_relation_requests()
+        self.assertEqual(len(event_ids), 1)
+        self.assertIn(RelationTypes.ANNOTATION, relations)
+
+        # The aggregation should exist.
+        chunk = self._get_aggregations()
+        self.assertEqual(chunk, [{"type": "m.reaction", "key": "👍", "count": 1}])
+
+        # Redact the original event.
+        self._redact(self.parent_id)
+
+        # The relations are returned.
+        event_ids, relations = self._make_relation_requests()
+        self.assertEquals(event_ids, [related_event_id])
+        self.assertEquals(
+            relations["m.annotation"],
+            {"chunk": [{"type": "m.reaction", "key": "👍", "count": 1}]},
+        )
+
+        # There's nothing to aggregate.
+        chunk = self._get_aggregations()
+        self.assertEqual(chunk, [{"count": 1, "key": "👍", "type": "m.reaction"}])
+
+    @unittest.override_config({"experimental_features": {"msc3440_enabled": True}})
+    def test_redact_parent_thread(self) -> None:
+        """
+        Test that thread replies are still available when the root event is redacted.
+        """
+        channel = self._send_relation(
+            RelationTypes.THREAD,
+            EventTypes.Message,
+            content={"body": "reply 1", "msgtype": "m.text"},
+        )
+        self.assertEqual(200, channel.code, channel.json_body)
+        related_event_id = channel.json_body["event_id"]
+
+        # Redact one of the reactions.
+        self._redact(self.parent_id)
+
+        # The unredacted relation should still exist.
+        event_ids, relations = self._make_relation_requests()
+        self.assertEquals(len(event_ids), 1)
+        self.assertDictContainsSubset(
+            {
+                "count": 1,
+                "current_user_participated": True,
+            },
+            relations[RelationTypes.THREAD],
+        )
+        self.assertEqual(
+            relations[RelationTypes.THREAD]["latest_event"]["event_id"],
+            related_event_id,
+        )
diff --git a/tests/rest/client/test_report_event.py b/tests/rest/client/test_report_event.py
index ee6b0b9ebfb0..20a259fc4388 100644
--- a/tests/rest/client/test_report_event.py
+++ b/tests/rest/client/test_report_event.py
@@ -14,8 +14,13 @@
 
 import json
 
+from twisted.test.proto_helpers import MemoryReactor
+
 import synapse.rest.admin
 from synapse.rest.client import login, report_event, room
+from synapse.server import HomeServer
+from synapse.types import JsonDict
+from synapse.util import Clock
 
 from tests import unittest
 
@@ -28,7 +33,7 @@ class ReportEventTestCase(unittest.HomeserverTestCase):
         report_event.register_servlets,
     ]
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.admin_user = self.register_user("admin", "pass", admin=True)
         self.admin_user_tok = self.login("admin", "pass")
         self.other_user = self.register_user("user", "pass")
@@ -42,35 +47,35 @@ def prepare(self, reactor, clock, hs):
         self.event_id = resp["event_id"]
         self.report_path = f"rooms/{self.room_id}/report/{self.event_id}"
 
-    def test_reason_str_and_score_int(self):
+    def test_reason_str_and_score_int(self) -> None:
         data = {"reason": "this makes me sad", "score": -100}
         self._assert_status(200, data)
 
-    def test_no_reason(self):
+    def test_no_reason(self) -> None:
         data = {"score": 0}
         self._assert_status(200, data)
 
-    def test_no_score(self):
+    def test_no_score(self) -> None:
         data = {"reason": "this makes me sad"}
         self._assert_status(200, data)
 
-    def test_no_reason_and_no_score(self):
-        data = {}
+    def test_no_reason_and_no_score(self) -> None:
+        data: JsonDict = {}
         self._assert_status(200, data)
 
-    def test_reason_int_and_score_str(self):
+    def test_reason_int_and_score_str(self) -> None:
         data = {"reason": 10, "score": "string"}
         self._assert_status(400, data)
 
-    def test_reason_zero_and_score_blank(self):
+    def test_reason_zero_and_score_blank(self) -> None:
         data = {"reason": 0, "score": ""}
         self._assert_status(400, data)
 
-    def test_reason_and_score_null(self):
+    def test_reason_and_score_null(self) -> None:
         data = {"reason": None, "score": None}
         self._assert_status(400, data)
 
-    def _assert_status(self, response_status, data):
+    def _assert_status(self, response_status: int, data: JsonDict) -> None:
         channel = self.make_request(
             "POST",
             self.report_path,
diff --git a/tests/rest/client/test_retention.py b/tests/rest/client/test_retention.py
index f3bf8d0934e6..7b8fe6d02522 100644
--- a/tests/rest/client/test_retention.py
+++ b/tests/rest/client/test_retention.py
@@ -24,6 +24,7 @@
 from synapse.visibility import filter_events_for_client
 
 from tests import unittest
+from tests.unittest import override_config
 
 one_hour_ms = 3600000
 one_day_ms = one_hour_ms * 24
@@ -38,7 +39,10 @@ class RetentionTestCase(unittest.HomeserverTestCase):
 
     def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
         config = self.default_config()
-        config["retention"] = {
+
+        # merge this default retention config with anything that was specified in
+        # @override_config
+        retention_config = {
             "enabled": True,
             "default_policy": {
                 "min_lifetime": one_day_ms,
@@ -47,6 +51,8 @@ def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
             "allowed_lifetime_min": one_day_ms,
             "allowed_lifetime_max": one_day_ms * 3,
         }
+        retention_config.update(config.get("retention", {}))
+        config["retention"] = retention_config
 
         self.hs = self.setup_test_homeserver(config=config)
 
@@ -115,22 +121,20 @@ def test_retention_event_purged_without_state_event(self) -> None:
 
         self._test_retention_event_purged(room_id, one_day_ms * 2)
 
+    @override_config({"retention": {"purge_jobs": [{"interval": "5d"}]}})
     def test_visibility(self) -> None:
         """Tests that synapse.visibility.filter_events_for_client correctly filters out
-        outdated events
+        outdated events, even if the purge job hasn't got to them yet.
+
+        We do this by setting a very long time between purge jobs.
         """
         store = self.hs.get_datastores().main
         storage = self.hs.get_storage()
         room_id = self.helper.create_room_as(self.user_id, tok=self.token)
-        events = []
 
         # Send a first event, which should be filtered out at the end of the test.
         resp = self.helper.send(room_id=room_id, body="1", tok=self.token)
-
-        # Get the event from the store so that we end up with a FrozenEvent that we can
-        # give to filter_events_for_client. We need to do this now because the event won't
-        # be in the database anymore after it has expired.
-        events.append(self.get_success(store.get_event(resp.get("event_id"))))
+        first_event_id = resp.get("event_id")
 
         # Advance the time by 2 days. We're using the default retention policy, therefore
         # after this the first event will still be valid.
@@ -138,16 +142,17 @@ def test_visibility(self) -> None:
 
         # Send another event, which shouldn't get filtered out.
         resp = self.helper.send(room_id=room_id, body="2", tok=self.token)
-
         valid_event_id = resp.get("event_id")
 
-        events.append(self.get_success(store.get_event(valid_event_id)))
-
         # Advance the time by another 2 days. After this, the first event should be
         # outdated but not the second one.
         self.reactor.advance(one_day_ms * 2 / 1000)
 
-        # Run filter_events_for_client with our list of FrozenEvents.
+        # Fetch the events, and run filter_events_for_client on them
+        events = self.get_success(
+            store.get_events_as_list([first_event_id, valid_event_id])
+        )
+        self.assertEqual(2, len(events), "events retrieved from database")
         filtered_events = self.get_success(
             filter_events_for_client(storage, self.user_id, events)
         )
diff --git a/tests/rest/client/test_rooms.py b/tests/rest/client/test_rooms.py
index e0b11e726433..3a9617d6da8e 100644
--- a/tests/rest/client/test_rooms.py
+++ b/tests/rest/client/test_rooms.py
@@ -18,11 +18,12 @@
 """Tests REST events for /rooms paths."""
 
 import json
-from typing import Iterable, List
+from typing import Any, Dict, Iterable, List, Optional
 from unittest.mock import Mock, call
 from urllib import parse as urlparse
 
 from twisted.internet import defer
+from twisted.test.proto_helpers import MemoryReactor
 
 import synapse.rest.admin
 from synapse.api.constants import (
@@ -35,7 +36,9 @@
 from synapse.handlers.pagination import PurgeStatus
 from synapse.rest import admin
 from synapse.rest.client import account, directory, login, profile, room, sync
+from synapse.server import HomeServer
 from synapse.types import JsonDict, RoomAlias, UserID, create_requester
+from synapse.util import Clock
 from synapse.util.stringutils import random_string
 
 from tests import unittest
@@ -45,11 +48,11 @@
 
 
 class RoomBase(unittest.HomeserverTestCase):
-    rmcreator_id = None
+    rmcreator_id: Optional[str] = None
 
     servlets = [room.register_servlets, room.register_deprecated_servlets]
 
-    def make_homeserver(self, reactor, clock):
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
 
         self.hs = self.setup_test_homeserver(
             "red",
@@ -57,15 +60,15 @@ def make_homeserver(self, reactor, clock):
             federation_client=Mock(),
         )
 
-        self.hs.get_federation_handler = Mock()
+        self.hs.get_federation_handler = Mock()  # type: ignore[assignment]
         self.hs.get_federation_handler.return_value.maybe_backfill = Mock(
             return_value=make_awaitable(None)
         )
 
-        async def _insert_client_ip(*args, **kwargs):
+        async def _insert_client_ip(*args: Any, **kwargs: Any) -> None:
             return None
 
-        self.hs.get_datastores().main.insert_client_ip = _insert_client_ip
+        self.hs.get_datastores().main.insert_client_ip = _insert_client_ip  # type: ignore[assignment]
 
         return self.hs
 
@@ -76,7 +79,7 @@ class RoomPermissionsTestCase(RoomBase):
     user_id = "@sid1:red"
     rmcreator_id = "@notme:red"
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
 
         self.helper.auth_user_id = self.rmcreator_id
         # create some rooms under the name rmcreator_id
@@ -108,12 +111,12 @@ def prepare(self, reactor, clock, hs):
         # auth as user_id now
         self.helper.auth_user_id = self.user_id
 
-    def test_can_do_action(self):
+    def test_can_do_action(self) -> None:
         msg_content = b'{"msgtype":"m.text","body":"hello"}'
 
         seq = iter(range(100))
 
-        def send_msg_path():
+        def send_msg_path() -> str:
             return "/rooms/%s/send/m.room.message/mid%s" % (
                 self.created_rmid,
                 str(next(seq)),
@@ -148,7 +151,7 @@ def send_msg_path():
         channel = self.make_request("PUT", send_msg_path(), msg_content)
         self.assertEqual(403, channel.code, msg=channel.result["body"])
 
-    def test_topic_perms(self):
+    def test_topic_perms(self) -> None:
         topic_content = b'{"topic":"My Topic Name"}'
         topic_path = "/rooms/%s/state/m.room.topic" % self.created_rmid
 
@@ -214,14 +217,14 @@ def test_topic_perms(self):
         self.assertEqual(403, channel.code, msg=channel.result["body"])
 
     def _test_get_membership(
-        self, room=None, members: Iterable = frozenset(), expect_code=None
-    ):
+        self, room: str, members: Iterable = frozenset(), expect_code: int = 200
+    ) -> None:
         for member in members:
             path = "/rooms/%s/state/m.room.member/%s" % (room, member)
             channel = self.make_request("GET", path)
             self.assertEqual(expect_code, channel.code)
 
-    def test_membership_basic_room_perms(self):
+    def test_membership_basic_room_perms(self) -> None:
         # === room does not exist ===
         room = self.uncreated_rmid
         # get membership of self, get membership of other, uncreated room
@@ -241,7 +244,7 @@ def test_membership_basic_room_perms(self):
             self.helper.join(room=room, user=usr, expect_code=404)
             self.helper.leave(room=room, user=usr, expect_code=404)
 
-    def test_membership_private_room_perms(self):
+    def test_membership_private_room_perms(self) -> None:
         room = self.created_rmid
         # get membership of self, get membership of other, private room + invite
         # expect all 403s
@@ -264,7 +267,7 @@ def test_membership_private_room_perms(self):
             members=[self.user_id, self.rmcreator_id], room=room, expect_code=200
         )
 
-    def test_membership_public_room_perms(self):
+    def test_membership_public_room_perms(self) -> None:
         room = self.created_public_rmid
         # get membership of self, get membership of other, public room + invite
         # expect 403
@@ -287,7 +290,7 @@ def test_membership_public_room_perms(self):
             members=[self.user_id, self.rmcreator_id], room=room, expect_code=200
         )
 
-    def test_invited_permissions(self):
+    def test_invited_permissions(self) -> None:
         room = self.created_rmid
         self.helper.invite(room=room, src=self.rmcreator_id, targ=self.user_id)
 
@@ -310,7 +313,7 @@ def test_invited_permissions(self):
             expect_code=403,
         )
 
-    def test_joined_permissions(self):
+    def test_joined_permissions(self) -> None:
         room = self.created_rmid
         self.helper.invite(room=room, src=self.rmcreator_id, targ=self.user_id)
         self.helper.join(room=room, user=self.user_id)
@@ -348,7 +351,7 @@ def test_joined_permissions(self):
         # set left of self, expect 200
         self.helper.leave(room=room, user=self.user_id)
 
-    def test_leave_permissions(self):
+    def test_leave_permissions(self) -> None:
         room = self.created_rmid
         self.helper.invite(room=room, src=self.rmcreator_id, targ=self.user_id)
         self.helper.join(room=room, user=self.user_id)
@@ -383,7 +386,7 @@ def test_leave_permissions(self):
         )
 
     # tests the "from banned" line from the table in https://spec.matrix.org/unstable/client-server-api/#mroommember
-    def test_member_event_from_ban(self):
+    def test_member_event_from_ban(self) -> None:
         room = self.created_rmid
         self.helper.invite(room=room, src=self.rmcreator_id, targ=self.user_id)
         self.helper.join(room=room, user=self.user_id)
@@ -475,21 +478,21 @@ class RoomsMemberListTestCase(RoomBase):
 
     user_id = "@sid1:red"
 
-    def test_get_member_list(self):
+    def test_get_member_list(self) -> None:
         room_id = self.helper.create_room_as(self.user_id)
         channel = self.make_request("GET", "/rooms/%s/members" % room_id)
         self.assertEqual(200, channel.code, msg=channel.result["body"])
 
-    def test_get_member_list_no_room(self):
+    def test_get_member_list_no_room(self) -> None:
         channel = self.make_request("GET", "/rooms/roomdoesnotexist/members")
         self.assertEqual(403, channel.code, msg=channel.result["body"])
 
-    def test_get_member_list_no_permission(self):
+    def test_get_member_list_no_permission(self) -> None:
         room_id = self.helper.create_room_as("@some_other_guy:red")
         channel = self.make_request("GET", "/rooms/%s/members" % room_id)
         self.assertEqual(403, channel.code, msg=channel.result["body"])
 
-    def test_get_member_list_no_permission_with_at_token(self):
+    def test_get_member_list_no_permission_with_at_token(self) -> None:
         """
         Tests that a stranger to the room cannot get the member list
         (in the case that they use an at token).
@@ -509,7 +512,7 @@ def test_get_member_list_no_permission_with_at_token(self):
         )
         self.assertEqual(403, channel.code, msg=channel.result["body"])
 
-    def test_get_member_list_no_permission_former_member(self):
+    def test_get_member_list_no_permission_former_member(self) -> None:
         """
         Tests that a former member of the room can not get the member list.
         """
@@ -529,7 +532,7 @@ def test_get_member_list_no_permission_former_member(self):
         channel = self.make_request("GET", "/rooms/%s/members" % room_id)
         self.assertEqual(403, channel.code, msg=channel.result["body"])
 
-    def test_get_member_list_no_permission_former_member_with_at_token(self):
+    def test_get_member_list_no_permission_former_member_with_at_token(self) -> None:
         """
         Tests that a former member of the room can not get the member list
         (in the case that they use an at token).
@@ -569,7 +572,7 @@ def test_get_member_list_no_permission_former_member_with_at_token(self):
         )
         self.assertEqual(403, channel.code, msg=channel.result["body"])
 
-    def test_get_member_list_mixed_memberships(self):
+    def test_get_member_list_mixed_memberships(self) -> None:
         room_creator = "@some_other_guy:red"
         room_id = self.helper.create_room_as(room_creator)
         room_path = "/rooms/%s/members" % room_id
@@ -594,26 +597,26 @@ class RoomsCreateTestCase(RoomBase):
 
     user_id = "@sid1:red"
 
-    def test_post_room_no_keys(self):
+    def test_post_room_no_keys(self) -> None:
         # POST with no config keys, expect new room id
         channel = self.make_request("POST", "/createRoom", "{}")
 
         self.assertEqual(200, channel.code, channel.result)
         self.assertTrue("room_id" in channel.json_body)
 
-    def test_post_room_visibility_key(self):
+    def test_post_room_visibility_key(self) -> None:
         # POST with visibility config key, expect new room id
         channel = self.make_request("POST", "/createRoom", b'{"visibility":"private"}')
         self.assertEqual(200, channel.code)
         self.assertTrue("room_id" in channel.json_body)
 
-    def test_post_room_custom_key(self):
+    def test_post_room_custom_key(self) -> None:
         # POST with custom config keys, expect new room id
         channel = self.make_request("POST", "/createRoom", b'{"custom":"stuff"}')
         self.assertEqual(200, channel.code)
         self.assertTrue("room_id" in channel.json_body)
 
-    def test_post_room_known_and_unknown_keys(self):
+    def test_post_room_known_and_unknown_keys(self) -> None:
         # POST with custom + known config keys, expect new room id
         channel = self.make_request(
             "POST", "/createRoom", b'{"visibility":"private","custom":"things"}'
@@ -621,7 +624,7 @@ def test_post_room_known_and_unknown_keys(self):
         self.assertEqual(200, channel.code)
         self.assertTrue("room_id" in channel.json_body)
 
-    def test_post_room_invalid_content(self):
+    def test_post_room_invalid_content(self) -> None:
         # POST with invalid content / paths, expect 400
         channel = self.make_request("POST", "/createRoom", b'{"visibili')
         self.assertEqual(400, channel.code)
@@ -629,7 +632,7 @@ def test_post_room_invalid_content(self):
         channel = self.make_request("POST", "/createRoom", b'["hello"]')
         self.assertEqual(400, channel.code)
 
-    def test_post_room_invitees_invalid_mxid(self):
+    def test_post_room_invitees_invalid_mxid(self) -> None:
         # POST with invalid invitee, see https://github.com/matrix-org/synapse/issues/4088
         # Note the trailing space in the MXID here!
         channel = self.make_request(
@@ -638,7 +641,7 @@ def test_post_room_invitees_invalid_mxid(self):
         self.assertEqual(400, channel.code)
 
     @unittest.override_config({"rc_invites": {"per_room": {"burst_count": 3}}})
-    def test_post_room_invitees_ratelimit(self):
+    def test_post_room_invitees_ratelimit(self) -> None:
         """Test that invites sent when creating a room are ratelimited by a RateLimiter,
         which ratelimits them correctly, including by not limiting when the requester is
         exempt from ratelimiting.
@@ -674,7 +677,7 @@ def test_post_room_invitees_ratelimit(self):
         channel = self.make_request("POST", "/createRoom", content)
         self.assertEqual(200, channel.code)
 
-    def test_spam_checker_may_join_room(self):
+    def test_spam_checker_may_join_room(self) -> None:
         """Tests that the user_may_join_room spam checker callback is correctly bypassed
         when creating a new room.
         """
@@ -704,12 +707,12 @@ class RoomTopicTestCase(RoomBase):
 
     user_id = "@sid1:red"
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         # create the room
         self.room_id = self.helper.create_room_as(self.user_id)
         self.path = "/rooms/%s/state/m.room.topic" % (self.room_id,)
 
-    def test_invalid_puts(self):
+    def test_invalid_puts(self) -> None:
         # missing keys or invalid json
         channel = self.make_request("PUT", self.path, "{}")
         self.assertEqual(400, channel.code, msg=channel.result["body"])
@@ -736,7 +739,7 @@ def test_invalid_puts(self):
         channel = self.make_request("PUT", self.path, content)
         self.assertEqual(400, channel.code, msg=channel.result["body"])
 
-    def test_rooms_topic(self):
+    def test_rooms_topic(self) -> None:
         # nothing should be there
         channel = self.make_request("GET", self.path)
         self.assertEqual(404, channel.code, msg=channel.result["body"])
@@ -751,7 +754,7 @@ def test_rooms_topic(self):
         self.assertEqual(200, channel.code, msg=channel.result["body"])
         self.assert_dict(json.loads(content), channel.json_body)
 
-    def test_rooms_topic_with_extra_keys(self):
+    def test_rooms_topic_with_extra_keys(self) -> None:
         # valid put with extra keys
         content = '{"topic":"Seasons","subtopic":"Summer"}'
         channel = self.make_request("PUT", self.path, content)
@@ -768,10 +771,10 @@ class RoomMemberStateTestCase(RoomBase):
 
     user_id = "@sid1:red"
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.room_id = self.helper.create_room_as(self.user_id)
 
-    def test_invalid_puts(self):
+    def test_invalid_puts(self) -> None:
         path = "/rooms/%s/state/m.room.member/%s" % (self.room_id, self.user_id)
         # missing keys or invalid json
         channel = self.make_request("PUT", path, "{}")
@@ -801,7 +804,7 @@ def test_invalid_puts(self):
         channel = self.make_request("PUT", path, content.encode("ascii"))
         self.assertEqual(400, channel.code, msg=channel.result["body"])
 
-    def test_rooms_members_self(self):
+    def test_rooms_members_self(self) -> None:
         path = "/rooms/%s/state/m.room.member/%s" % (
             urlparse.quote(self.room_id),
             self.user_id,
@@ -812,13 +815,13 @@ def test_rooms_members_self(self):
         channel = self.make_request("PUT", path, content.encode("ascii"))
         self.assertEqual(200, channel.code, msg=channel.result["body"])
 
-        channel = self.make_request("GET", path, None)
+        channel = self.make_request("GET", path, content=b"")
         self.assertEqual(200, channel.code, msg=channel.result["body"])
 
         expected_response = {"membership": Membership.JOIN}
         self.assertEqual(expected_response, channel.json_body)
 
-    def test_rooms_members_other(self):
+    def test_rooms_members_other(self) -> None:
         self.other_id = "@zzsid1:red"
         path = "/rooms/%s/state/m.room.member/%s" % (
             urlparse.quote(self.room_id),
@@ -830,11 +833,11 @@ def test_rooms_members_other(self):
         channel = self.make_request("PUT", path, content)
         self.assertEqual(200, channel.code, msg=channel.result["body"])
 
-        channel = self.make_request("GET", path, None)
+        channel = self.make_request("GET", path, content=b"")
         self.assertEqual(200, channel.code, msg=channel.result["body"])
         self.assertEqual(json.loads(content), channel.json_body)
 
-    def test_rooms_members_other_custom_keys(self):
+    def test_rooms_members_other_custom_keys(self) -> None:
         self.other_id = "@zzsid1:red"
         path = "/rooms/%s/state/m.room.member/%s" % (
             urlparse.quote(self.room_id),
@@ -849,7 +852,7 @@ def test_rooms_members_other_custom_keys(self):
         channel = self.make_request("PUT", path, content)
         self.assertEqual(200, channel.code, msg=channel.result["body"])
 
-        channel = self.make_request("GET", path, None)
+        channel = self.make_request("GET", path, content=b"")
         self.assertEqual(200, channel.code, msg=channel.result["body"])
         self.assertEqual(json.loads(content), channel.json_body)
 
@@ -866,7 +869,7 @@ class RoomInviteRatelimitTestCase(RoomBase):
     @unittest.override_config(
         {"rc_invites": {"per_room": {"per_second": 0.5, "burst_count": 3}}}
     )
-    def test_invites_by_rooms_ratelimit(self):
+    def test_invites_by_rooms_ratelimit(self) -> None:
         """Tests that invites in a room are actually rate-limited."""
         room_id = self.helper.create_room_as(self.user_id)
 
@@ -878,7 +881,7 @@ def test_invites_by_rooms_ratelimit(self):
     @unittest.override_config(
         {"rc_invites": {"per_user": {"per_second": 0.5, "burst_count": 3}}}
     )
-    def test_invites_by_users_ratelimit(self):
+    def test_invites_by_users_ratelimit(self) -> None:
         """Tests that invites to a specific user are actually rate-limited."""
 
         for _ in range(3):
@@ -897,7 +900,7 @@ class RoomJoinTestCase(RoomBase):
         room.register_servlets,
     ]
 
-    def prepare(self, reactor, clock, homeserver):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.user1 = self.register_user("thomas", "hackme")
         self.tok1 = self.login("thomas", "hackme")
 
@@ -908,7 +911,7 @@ def prepare(self, reactor, clock, homeserver):
         self.room2 = self.helper.create_room_as(room_creator=self.user1, tok=self.tok1)
         self.room3 = self.helper.create_room_as(room_creator=self.user1, tok=self.tok1)
 
-    def test_spam_checker_may_join_room(self):
+    def test_spam_checker_may_join_room(self) -> None:
         """Tests that the user_may_join_room spam checker callback is correctly called
         and blocks room joins when needed.
         """
@@ -975,8 +978,8 @@ class RoomJoinRatelimitTestCase(RoomBase):
         room.register_servlets,
     ]
 
-    def prepare(self, reactor, clock, homeserver):
-        super().prepare(reactor, clock, homeserver)
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        super().prepare(reactor, clock, hs)
         # profile changes expect that the user is actually registered
         user = UserID.from_string(self.user_id)
         self.get_success(self.register_user(user.localpart, "supersecretpassword"))
@@ -984,7 +987,7 @@ def prepare(self, reactor, clock, homeserver):
     @unittest.override_config(
         {"rc_joins": {"local": {"per_second": 0.5, "burst_count": 3}}}
     )
-    def test_join_local_ratelimit(self):
+    def test_join_local_ratelimit(self) -> None:
         """Tests that local joins are actually rate-limited."""
         for _ in range(3):
             self.helper.create_room_as(self.user_id)
@@ -994,7 +997,7 @@ def test_join_local_ratelimit(self):
     @unittest.override_config(
         {"rc_joins": {"local": {"per_second": 0.5, "burst_count": 3}}}
     )
-    def test_join_local_ratelimit_profile_change(self):
+    def test_join_local_ratelimit_profile_change(self) -> None:
         """Tests that sending a profile update into all of the user's joined rooms isn't
         rate-limited by the rate-limiter on joins."""
 
@@ -1031,7 +1034,7 @@ def test_join_local_ratelimit_profile_change(self):
     @unittest.override_config(
         {"rc_joins": {"local": {"per_second": 0.5, "burst_count": 3}}}
     )
-    def test_join_local_ratelimit_idempotent(self):
+    def test_join_local_ratelimit_idempotent(self) -> None:
         """Tests that the room join endpoints remain idempotent despite rate-limiting
         on room joins."""
         room_id = self.helper.create_room_as(self.user_id)
@@ -1056,7 +1059,7 @@ def test_join_local_ratelimit_idempotent(self):
             "autocreate_auto_join_rooms": True,
         },
     )
-    def test_autojoin_rooms(self):
+    def test_autojoin_rooms(self) -> None:
         user_id = self.register_user("testuser", "password")
 
         # Check that the new user successfully joined the four rooms
@@ -1071,10 +1074,10 @@ class RoomMessagesTestCase(RoomBase):
 
     user_id = "@sid1:red"
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.room_id = self.helper.create_room_as(self.user_id)
 
-    def test_invalid_puts(self):
+    def test_invalid_puts(self) -> None:
         path = "/rooms/%s/send/m.room.message/mid1" % (urlparse.quote(self.room_id))
         # missing keys or invalid json
         channel = self.make_request("PUT", path, b"{}")
@@ -1095,7 +1098,7 @@ def test_invalid_puts(self):
         channel = self.make_request("PUT", path, b"")
         self.assertEqual(400, channel.code, msg=channel.result["body"])
 
-    def test_rooms_messages_sent(self):
+    def test_rooms_messages_sent(self) -> None:
         path = "/rooms/%s/send/m.room.message/mid1" % (urlparse.quote(self.room_id))
 
         content = b'{"body":"test","msgtype":{"type":"a"}}'
@@ -1119,11 +1122,11 @@ class RoomInitialSyncTestCase(RoomBase):
 
     user_id = "@sid1:red"
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         # create the room
         self.room_id = self.helper.create_room_as(self.user_id)
 
-    def test_initial_sync(self):
+    def test_initial_sync(self) -> None:
         channel = self.make_request("GET", "/rooms/%s/initialSync" % self.room_id)
         self.assertEqual(200, channel.code)
 
@@ -1131,7 +1134,7 @@ def test_initial_sync(self):
         self.assertEqual("join", channel.json_body["membership"])
 
         # Room state is easier to assert on if we unpack it into a dict
-        state = {}
+        state: JsonDict = {}
         for event in channel.json_body["state"]:
             if "state_key" not in event:
                 continue
@@ -1160,10 +1163,10 @@ class RoomMessageListTestCase(RoomBase):
 
     user_id = "@sid1:red"
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.room_id = self.helper.create_room_as(self.user_id)
 
-    def test_topo_token_is_accepted(self):
+    def test_topo_token_is_accepted(self) -> None:
         token = "t1-0_0_0_0_0_0_0_0_0"
         channel = self.make_request(
             "GET", "/rooms/%s/messages?access_token=x&from=%s" % (self.room_id, token)
@@ -1174,7 +1177,7 @@ def test_topo_token_is_accepted(self):
         self.assertTrue("chunk" in channel.json_body)
         self.assertTrue("end" in channel.json_body)
 
-    def test_stream_token_is_accepted_for_fwd_pagianation(self):
+    def test_stream_token_is_accepted_for_fwd_pagianation(self) -> None:
         token = "s0_0_0_0_0_0_0_0_0"
         channel = self.make_request(
             "GET", "/rooms/%s/messages?access_token=x&from=%s" % (self.room_id, token)
@@ -1185,7 +1188,7 @@ def test_stream_token_is_accepted_for_fwd_pagianation(self):
         self.assertTrue("chunk" in channel.json_body)
         self.assertTrue("end" in channel.json_body)
 
-    def test_room_messages_purge(self):
+    def test_room_messages_purge(self) -> None:
         store = self.hs.get_datastores().main
         pagination_handler = self.hs.get_pagination_handler()
 
@@ -1278,10 +1281,10 @@ class RoomSearchTestCase(unittest.HomeserverTestCase):
     user_id = True
     hijack_auth = False
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
 
         # Register the user who does the searching
-        self.user_id = self.register_user("user", "pass")
+        self.user_id2 = self.register_user("user", "pass")
         self.access_token = self.login("user", "pass")
 
         # Register the user who sends the message
@@ -1289,12 +1292,12 @@ def prepare(self, reactor, clock, hs):
         self.other_access_token = self.login("otheruser", "pass")
 
         # Create a room
-        self.room = self.helper.create_room_as(self.user_id, tok=self.access_token)
+        self.room = self.helper.create_room_as(self.user_id2, tok=self.access_token)
 
         # Invite the other person
         self.helper.invite(
             room=self.room,
-            src=self.user_id,
+            src=self.user_id2,
             tok=self.access_token,
             targ=self.other_user_id,
         )
@@ -1304,7 +1307,7 @@ def prepare(self, reactor, clock, hs):
             room=self.room, user=self.other_user_id, tok=self.other_access_token
         )
 
-    def test_finds_message(self):
+    def test_finds_message(self) -> None:
         """
         The search functionality will search for content in messages if asked to
         do so.
@@ -1333,7 +1336,7 @@ def test_finds_message(self):
         # No context was requested, so we should get none.
         self.assertEqual(results["results"][0]["context"], {})
 
-    def test_include_context(self):
+    def test_include_context(self) -> None:
         """
         When event_context includes include_profile, profile information will be
         included in the search response.
@@ -1379,7 +1382,7 @@ class PublicRoomsRestrictedTestCase(unittest.HomeserverTestCase):
         login.register_servlets,
     ]
 
-    def make_homeserver(self, reactor, clock):
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
 
         self.url = b"/_matrix/client/r0/publicRooms"
 
@@ -1389,11 +1392,11 @@ def make_homeserver(self, reactor, clock):
 
         return self.hs
 
-    def test_restricted_no_auth(self):
+    def test_restricted_no_auth(self) -> None:
         channel = self.make_request("GET", self.url)
         self.assertEqual(channel.code, 401, channel.result)
 
-    def test_restricted_auth(self):
+    def test_restricted_auth(self) -> None:
         self.register_user("user", "pass")
         tok = self.login("user", "pass")
 
@@ -1412,19 +1415,19 @@ class PublicRoomsTestRemoteSearchFallbackTestCase(unittest.HomeserverTestCase):
         login.register_servlets,
     ]
 
-    def make_homeserver(self, reactor, clock):
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
         return self.setup_test_homeserver(federation_client=Mock())
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.register_user("user", "pass")
         self.token = self.login("user", "pass")
 
         self.federation_client = hs.get_federation_client()
 
-    def test_simple(self):
+    def test_simple(self) -> None:
         "Simple test for searching rooms over federation"
-        self.federation_client.get_public_rooms.side_effect = (
-            lambda *a, **k: defer.succeed({})
+        self.federation_client.get_public_rooms.side_effect = lambda *a, **k: defer.succeed(  # type: ignore[attr-defined]
+            {}
         )
 
         search_filter = {"generic_search_term": "foobar"}
@@ -1437,7 +1440,7 @@ def test_simple(self):
         )
         self.assertEqual(channel.code, 200, channel.result)
 
-        self.federation_client.get_public_rooms.assert_called_once_with(
+        self.federation_client.get_public_rooms.assert_called_once_with(  # type: ignore[attr-defined]
             "testserv",
             limit=100,
             since_token=None,
@@ -1446,12 +1449,12 @@ def test_simple(self):
             third_party_instance_id=None,
         )
 
-    def test_fallback(self):
+    def test_fallback(self) -> None:
         "Test that searching public rooms over federation falls back if it gets a 404"
 
         # The `get_public_rooms` should be called again if the first call fails
         # with a 404, when using search filters.
-        self.federation_client.get_public_rooms.side_effect = (
+        self.federation_client.get_public_rooms.side_effect = (  # type: ignore[attr-defined]
             HttpResponseException(404, "Not Found", b""),
             defer.succeed({}),
         )
@@ -1466,7 +1469,7 @@ def test_fallback(self):
         )
         self.assertEqual(channel.code, 200, channel.result)
 
-        self.federation_client.get_public_rooms.assert_has_calls(
+        self.federation_client.get_public_rooms.assert_has_calls(  # type: ignore[attr-defined]
             [
                 call(
                     "testserv",
@@ -1497,14 +1500,14 @@ class PerRoomProfilesForbiddenTestCase(unittest.HomeserverTestCase):
         profile.register_servlets,
     ]
 
-    def make_homeserver(self, reactor, clock):
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
         config = self.default_config()
         config["allow_per_room_profiles"] = False
         self.hs = self.setup_test_homeserver(config=config)
 
         return self.hs
 
-    def prepare(self, reactor, clock, homeserver):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.user_id = self.register_user("test", "test")
         self.tok = self.login("test", "test")
 
@@ -1522,7 +1525,7 @@ def prepare(self, reactor, clock, homeserver):
 
         self.room_id = self.helper.create_room_as(self.user_id, tok=self.tok)
 
-    def test_per_room_profile_forbidden(self):
+    def test_per_room_profile_forbidden(self) -> None:
         data = {"membership": "join", "displayname": "other test user"}
         request_data = json.dumps(data)
         channel = self.make_request(
@@ -1557,7 +1560,7 @@ class RoomMembershipReasonTestCase(unittest.HomeserverTestCase):
         login.register_servlets,
     ]
 
-    def prepare(self, reactor, clock, homeserver):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.creator = self.register_user("creator", "test")
         self.creator_tok = self.login("creator", "test")
 
@@ -1566,7 +1569,7 @@ def prepare(self, reactor, clock, homeserver):
 
         self.room_id = self.helper.create_room_as(self.creator, tok=self.creator_tok)
 
-    def test_join_reason(self):
+    def test_join_reason(self) -> None:
         reason = "hello"
         channel = self.make_request(
             "POST",
@@ -1578,7 +1581,7 @@ def test_join_reason(self):
 
         self._check_for_reason(reason)
 
-    def test_leave_reason(self):
+    def test_leave_reason(self) -> None:
         self.helper.join(self.room_id, user=self.second_user_id, tok=self.second_tok)
 
         reason = "hello"
@@ -1592,7 +1595,7 @@ def test_leave_reason(self):
 
         self._check_for_reason(reason)
 
-    def test_kick_reason(self):
+    def test_kick_reason(self) -> None:
         self.helper.join(self.room_id, user=self.second_user_id, tok=self.second_tok)
 
         reason = "hello"
@@ -1606,7 +1609,7 @@ def test_kick_reason(self):
 
         self._check_for_reason(reason)
 
-    def test_ban_reason(self):
+    def test_ban_reason(self) -> None:
         self.helper.join(self.room_id, user=self.second_user_id, tok=self.second_tok)
 
         reason = "hello"
@@ -1620,7 +1623,7 @@ def test_ban_reason(self):
 
         self._check_for_reason(reason)
 
-    def test_unban_reason(self):
+    def test_unban_reason(self) -> None:
         reason = "hello"
         channel = self.make_request(
             "POST",
@@ -1632,7 +1635,7 @@ def test_unban_reason(self):
 
         self._check_for_reason(reason)
 
-    def test_invite_reason(self):
+    def test_invite_reason(self) -> None:
         reason = "hello"
         channel = self.make_request(
             "POST",
@@ -1644,7 +1647,7 @@ def test_invite_reason(self):
 
         self._check_for_reason(reason)
 
-    def test_reject_invite_reason(self):
+    def test_reject_invite_reason(self) -> None:
         self.helper.invite(
             self.room_id,
             src=self.creator,
@@ -1663,7 +1666,7 @@ def test_reject_invite_reason(self):
 
         self._check_for_reason(reason)
 
-    def _check_for_reason(self, reason):
+    def _check_for_reason(self, reason: str) -> None:
         channel = self.make_request(
             "GET",
             "/_matrix/client/r0/rooms/{}/state/m.room.member/{}".format(
@@ -1704,12 +1707,12 @@ class LabelsTestCase(unittest.HomeserverTestCase):
         "org.matrix.not_labels": ["#notfun"],
     }
 
-    def prepare(self, reactor, clock, homeserver):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.user_id = self.register_user("test", "test")
         self.tok = self.login("test", "test")
         self.room_id = self.helper.create_room_as(self.user_id, tok=self.tok)
 
-    def test_context_filter_labels(self):
+    def test_context_filter_labels(self) -> None:
         """Test that we can filter by a label on a /context request."""
         event_id = self._send_labelled_messages_in_room()
 
@@ -1739,7 +1742,7 @@ def test_context_filter_labels(self):
             events_after[0]["content"]["body"], "with right label", events_after[0]
         )
 
-    def test_context_filter_not_labels(self):
+    def test_context_filter_not_labels(self) -> None:
         """Test that we can filter by the absence of a label on a /context request."""
         event_id = self._send_labelled_messages_in_room()
 
@@ -1772,7 +1775,7 @@ def test_context_filter_not_labels(self):
             events_after[1]["content"]["body"], "with two wrong labels", events_after[1]
         )
 
-    def test_context_filter_labels_not_labels(self):
+    def test_context_filter_labels_not_labels(self) -> None:
         """Test that we can filter by both a label and the absence of another label on a
         /context request.
         """
@@ -1801,7 +1804,7 @@ def test_context_filter_labels_not_labels(self):
             events_after[0]["content"]["body"], "with wrong label", events_after[0]
         )
 
-    def test_messages_filter_labels(self):
+    def test_messages_filter_labels(self) -> None:
         """Test that we can filter by a label on a /messages request."""
         self._send_labelled_messages_in_room()
 
@@ -1818,7 +1821,7 @@ def test_messages_filter_labels(self):
         self.assertEqual(events[0]["content"]["body"], "with right label", events[0])
         self.assertEqual(events[1]["content"]["body"], "with right label", events[1])
 
-    def test_messages_filter_not_labels(self):
+    def test_messages_filter_not_labels(self) -> None:
         """Test that we can filter by the absence of a label on a /messages request."""
         self._send_labelled_messages_in_room()
 
@@ -1839,7 +1842,7 @@ def test_messages_filter_not_labels(self):
             events[3]["content"]["body"], "with two wrong labels", events[3]
         )
 
-    def test_messages_filter_labels_not_labels(self):
+    def test_messages_filter_labels_not_labels(self) -> None:
         """Test that we can filter by both a label and the absence of another label on a
         /messages request.
         """
@@ -1862,7 +1865,7 @@ def test_messages_filter_labels_not_labels(self):
         self.assertEqual(len(events), 1, [event["content"] for event in events])
         self.assertEqual(events[0]["content"]["body"], "with wrong label", events[0])
 
-    def test_search_filter_labels(self):
+    def test_search_filter_labels(self) -> None:
         """Test that we can filter by a label on a /search request."""
         request_data = json.dumps(
             {
@@ -1899,7 +1902,7 @@ def test_search_filter_labels(self):
             results[1]["result"]["content"]["body"],
         )
 
-    def test_search_filter_not_labels(self):
+    def test_search_filter_not_labels(self) -> None:
         """Test that we can filter by the absence of a label on a /search request."""
         request_data = json.dumps(
             {
@@ -1946,7 +1949,7 @@ def test_search_filter_not_labels(self):
             results[3]["result"]["content"]["body"],
         )
 
-    def test_search_filter_labels_not_labels(self):
+    def test_search_filter_labels_not_labels(self) -> None:
         """Test that we can filter by both a label and the absence of another label on a
         /search request.
         """
@@ -1980,7 +1983,7 @@ def test_search_filter_labels_not_labels(self):
             results[0]["result"]["content"]["body"],
         )
 
-    def _send_labelled_messages_in_room(self):
+    def _send_labelled_messages_in_room(self) -> str:
         """Sends several messages to a room with different labels (or without any) to test
         filtering by label.
         Returns:
@@ -2056,12 +2059,12 @@ class RelationsTestCase(unittest.HomeserverTestCase):
         login.register_servlets,
     ]
 
-    def default_config(self):
+    def default_config(self) -> Dict[str, Any]:
         config = super().default_config()
         config["experimental_features"] = {"msc3440_enabled": True}
         return config
 
-    def prepare(self, reactor, clock, homeserver):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.user_id = self.register_user("test", "test")
         self.tok = self.login("test", "test")
         self.room_id = self.helper.create_room_as(self.user_id, tok=self.tok)
@@ -2136,45 +2139,43 @@ def _filter_messages(self, filter: JsonDict) -> List[JsonDict]:
 
         return channel.json_body["chunk"]
 
-    def test_filter_relation_senders(self):
+    def test_filter_relation_senders(self) -> None:
         # Messages which second user reacted to.
-        filter = {"io.element.relation_senders": [self.second_user_id]}
+        filter = {"related_by_senders": [self.second_user_id]}
         chunk = self._filter_messages(filter)
         self.assertEqual(len(chunk), 1, chunk)
         self.assertEqual(chunk[0]["event_id"], self.event_id_1)
 
         # Messages which third user reacted to.
-        filter = {"io.element.relation_senders": [self.third_user_id]}
+        filter = {"related_by_senders": [self.third_user_id]}
         chunk = self._filter_messages(filter)
         self.assertEqual(len(chunk), 1, chunk)
         self.assertEqual(chunk[0]["event_id"], self.event_id_2)
 
         # Messages which either user reacted to.
-        filter = {
-            "io.element.relation_senders": [self.second_user_id, self.third_user_id]
-        }
+        filter = {"related_by_senders": [self.second_user_id, self.third_user_id]}
         chunk = self._filter_messages(filter)
         self.assertEqual(len(chunk), 2, chunk)
         self.assertCountEqual(
             [c["event_id"] for c in chunk], [self.event_id_1, self.event_id_2]
         )
 
-    def test_filter_relation_type(self):
+    def test_filter_relation_type(self) -> None:
         # Messages which have annotations.
-        filter = {"io.element.relation_types": [RelationTypes.ANNOTATION]}
+        filter = {"related_by_rel_types": [RelationTypes.ANNOTATION]}
         chunk = self._filter_messages(filter)
         self.assertEqual(len(chunk), 1, chunk)
         self.assertEqual(chunk[0]["event_id"], self.event_id_1)
 
         # Messages which have references.
-        filter = {"io.element.relation_types": [RelationTypes.REFERENCE]}
+        filter = {"related_by_rel_types": [RelationTypes.REFERENCE]}
         chunk = self._filter_messages(filter)
         self.assertEqual(len(chunk), 1, chunk)
         self.assertEqual(chunk[0]["event_id"], self.event_id_2)
 
         # Messages which have either annotations or references.
         filter = {
-            "io.element.relation_types": [
+            "related_by_rel_types": [
                 RelationTypes.ANNOTATION,
                 RelationTypes.REFERENCE,
             ]
@@ -2185,11 +2186,11 @@ def test_filter_relation_type(self):
             [c["event_id"] for c in chunk], [self.event_id_1, self.event_id_2]
         )
 
-    def test_filter_relation_senders_and_type(self):
+    def test_filter_relation_senders_and_type(self) -> None:
         # Messages which second user reacted to.
         filter = {
-            "io.element.relation_senders": [self.second_user_id],
-            "io.element.relation_types": [RelationTypes.ANNOTATION],
+            "related_by_senders": [self.second_user_id],
+            "related_by_rel_types": [RelationTypes.ANNOTATION],
         }
         chunk = self._filter_messages(filter)
         self.assertEqual(len(chunk), 1, chunk)
@@ -2205,7 +2206,7 @@ class ContextTestCase(unittest.HomeserverTestCase):
         account.register_servlets,
     ]
 
-    def prepare(self, reactor, clock, homeserver):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.user_id = self.register_user("user", "password")
         self.tok = self.login("user", "password")
         self.room_id = self.helper.create_room_as(
@@ -2218,7 +2219,7 @@ def prepare(self, reactor, clock, homeserver):
         self.helper.invite(self.room_id, self.user_id, self.other_user_id, tok=self.tok)
         self.helper.join(self.room_id, self.other_user_id, tok=self.other_tok)
 
-    def test_erased_sender(self):
+    def test_erased_sender(self) -> None:
         """Test that an erasure request results in the requester's events being hidden
         from any new member of the room.
         """
@@ -2332,7 +2333,7 @@ class RoomAliasListTestCase(unittest.HomeserverTestCase):
         room.register_servlets,
     ]
 
-    def prepare(self, reactor, clock, homeserver):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.room_owner = self.register_user("room_owner", "test")
         self.room_owner_tok = self.login("room_owner", "test")
 
@@ -2340,17 +2341,17 @@ def prepare(self, reactor, clock, homeserver):
             self.room_owner, tok=self.room_owner_tok
         )
 
-    def test_no_aliases(self):
+    def test_no_aliases(self) -> None:
         res = self._get_aliases(self.room_owner_tok)
         self.assertEqual(res["aliases"], [])
 
-    def test_not_in_room(self):
+    def test_not_in_room(self) -> None:
         self.register_user("user", "test")
         user_tok = self.login("user", "test")
         res = self._get_aliases(user_tok, expected_code=403)
         self.assertEqual(res["errcode"], "M_FORBIDDEN")
 
-    def test_admin_user(self):
+    def test_admin_user(self) -> None:
         alias1 = self._random_alias()
         self._set_alias_via_directory(alias1)
 
@@ -2360,7 +2361,7 @@ def test_admin_user(self):
         res = self._get_aliases(user_tok)
         self.assertEqual(res["aliases"], [alias1])
 
-    def test_with_aliases(self):
+    def test_with_aliases(self) -> None:
         alias1 = self._random_alias()
         alias2 = self._random_alias()
 
@@ -2370,7 +2371,7 @@ def test_with_aliases(self):
         res = self._get_aliases(self.room_owner_tok)
         self.assertEqual(set(res["aliases"]), {alias1, alias2})
 
-    def test_peekable_room(self):
+    def test_peekable_room(self) -> None:
         alias1 = self._random_alias()
         self._set_alias_via_directory(alias1)
 
@@ -2404,7 +2405,7 @@ def _get_aliases(self, access_token: str, expected_code: int = 200) -> JsonDict:
     def _random_alias(self) -> str:
         return RoomAlias(random_string(5), self.hs.hostname).to_string()
 
-    def _set_alias_via_directory(self, alias: str, expected_code: int = 200):
+    def _set_alias_via_directory(self, alias: str, expected_code: int = 200) -> None:
         url = "/_matrix/client/r0/directory/room/" + alias
         data = {"room_id": self.room_id}
         request_data = json.dumps(data)
@@ -2423,7 +2424,7 @@ class RoomCanonicalAliasTestCase(unittest.HomeserverTestCase):
         room.register_servlets,
     ]
 
-    def prepare(self, reactor, clock, homeserver):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.room_owner = self.register_user("room_owner", "test")
         self.room_owner_tok = self.login("room_owner", "test")
 
@@ -2434,7 +2435,7 @@ def prepare(self, reactor, clock, homeserver):
         self.alias = "#alias:test"
         self._set_alias_via_directory(self.alias)
 
-    def _set_alias_via_directory(self, alias: str, expected_code: int = 200):
+    def _set_alias_via_directory(self, alias: str, expected_code: int = 200) -> None:
         url = "/_matrix/client/r0/directory/room/" + alias
         data = {"room_id": self.room_id}
         request_data = json.dumps(data)
@@ -2456,7 +2457,9 @@ def _get_canonical_alias(self, expected_code: int = 200) -> JsonDict:
         self.assertIsInstance(res, dict)
         return res
 
-    def _set_canonical_alias(self, content: str, expected_code: int = 200) -> JsonDict:
+    def _set_canonical_alias(
+        self, content: JsonDict, expected_code: int = 200
+    ) -> JsonDict:
         """Calls the endpoint under test. returns the json response object."""
         channel = self.make_request(
             "PUT",
@@ -2469,7 +2472,7 @@ def _set_canonical_alias(self, content: str, expected_code: int = 200) -> JsonDi
         self.assertIsInstance(res, dict)
         return res
 
-    def test_canonical_alias(self):
+    def test_canonical_alias(self) -> None:
         """Test a basic alias message."""
         # There is no canonical alias to start with.
         self._get_canonical_alias(expected_code=404)
@@ -2488,7 +2491,7 @@ def test_canonical_alias(self):
         res = self._get_canonical_alias()
         self.assertEqual(res, {})
 
-    def test_alt_aliases(self):
+    def test_alt_aliases(self) -> None:
         """Test a canonical alias message with alt_aliases."""
         # Create an alias.
         self._set_canonical_alias({"alt_aliases": [self.alias]})
@@ -2504,7 +2507,7 @@ def test_alt_aliases(self):
         res = self._get_canonical_alias()
         self.assertEqual(res, {})
 
-    def test_alias_alt_aliases(self):
+    def test_alias_alt_aliases(self) -> None:
         """Test a canonical alias message with an alias and alt_aliases."""
         # Create an alias.
         self._set_canonical_alias({"alias": self.alias, "alt_aliases": [self.alias]})
@@ -2520,7 +2523,7 @@ def test_alias_alt_aliases(self):
         res = self._get_canonical_alias()
         self.assertEqual(res, {})
 
-    def test_partial_modify(self):
+    def test_partial_modify(self) -> None:
         """Test removing only the alt_aliases."""
         # Create an alias.
         self._set_canonical_alias({"alias": self.alias, "alt_aliases": [self.alias]})
@@ -2536,7 +2539,7 @@ def test_partial_modify(self):
         res = self._get_canonical_alias()
         self.assertEqual(res, {"alias": self.alias})
 
-    def test_add_alias(self):
+    def test_add_alias(self) -> None:
         """Test removing only the alt_aliases."""
         # Create an additional alias.
         second_alias = "#second:test"
@@ -2556,7 +2559,7 @@ def test_add_alias(self):
             res, {"alias": self.alias, "alt_aliases": [self.alias, second_alias]}
         )
 
-    def test_bad_data(self):
+    def test_bad_data(self) -> None:
         """Invalid data for alt_aliases should cause errors."""
         self._set_canonical_alias({"alt_aliases": "@bad:test"}, expected_code=400)
         self._set_canonical_alias({"alt_aliases": None}, expected_code=400)
@@ -2566,7 +2569,7 @@ def test_bad_data(self):
         self._set_canonical_alias({"alt_aliases": True}, expected_code=400)
         self._set_canonical_alias({"alt_aliases": {}}, expected_code=400)
 
-    def test_bad_alias(self):
+    def test_bad_alias(self) -> None:
         """An alias which does not point to the room raises a SynapseError."""
         self._set_canonical_alias({"alias": "@unknown:test"}, expected_code=400)
         self._set_canonical_alias({"alt_aliases": ["@unknown:test"]}, expected_code=400)
@@ -2580,13 +2583,13 @@ class ThreepidInviteTestCase(unittest.HomeserverTestCase):
         room.register_servlets,
     ]
 
-    def prepare(self, reactor, clock, homeserver):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.user_id = self.register_user("thomas", "hackme")
         self.tok = self.login("thomas", "hackme")
 
         self.room_id = self.helper.create_room_as(self.user_id, tok=self.tok)
 
-    def test_threepid_invite_spamcheck(self):
+    def test_threepid_invite_spamcheck(self) -> None:
         # Mock a few functions to prevent the test from failing due to failing to talk to
         # a remote IS. We keep the mock for _mock_make_and_store_3pid_invite around so we
         # can check its call_count later on during the test.
diff --git a/tests/rest/client/test_third_party_rules.py b/tests/rest/client/test_third_party_rules.py
index bfc04785b7b2..e7de67e3a3b0 100644
--- a/tests/rest/client/test_third_party_rules.py
+++ b/tests/rest/client/test_third_party_rules.py
@@ -12,16 +12,22 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import threading
-from typing import TYPE_CHECKING, Dict, Optional, Tuple
+from typing import TYPE_CHECKING, Any, Dict, Optional, Tuple, Union
 from unittest.mock import Mock
 
+from twisted.test.proto_helpers import MemoryReactor
+
 from synapse.api.constants import EventTypes, LoginType, Membership
 from synapse.api.errors import SynapseError
+from synapse.api.room_versions import RoomVersion
 from synapse.events import EventBase
+from synapse.events.snapshot import EventContext
 from synapse.events.third_party_rules import load_legacy_third_party_event_rules
 from synapse.rest import admin
 from synapse.rest.client import account, login, profile, room
+from synapse.server import HomeServer
 from synapse.types import JsonDict, Requester, StateMap
+from synapse.util import Clock
 from synapse.util.frozenutils import unfreeze
 
 from tests import unittest
@@ -34,7 +40,7 @@
 
 
 class LegacyThirdPartyRulesTestModule:
-    def __init__(self, config: Dict, module_api: "ModuleApi"):
+    def __init__(self, config: Dict, module_api: "ModuleApi") -> None:
         # keep a record of the "current" rules module, so that the test can patch
         # it if desired.
         thread_local.rules_module = self
@@ -42,32 +48,36 @@ def __init__(self, config: Dict, module_api: "ModuleApi"):
 
     async def on_create_room(
         self, requester: Requester, config: dict, is_requester_admin: bool
-    ):
+    ) -> bool:
         return True
 
-    async def check_event_allowed(self, event: EventBase, state: StateMap[EventBase]):
+    async def check_event_allowed(
+        self, event: EventBase, state: StateMap[EventBase]
+    ) -> Union[bool, dict]:
         return True
 
     @staticmethod
-    def parse_config(config):
+    def parse_config(config: Dict[str, Any]) -> Dict[str, Any]:
         return config
 
 
 class LegacyDenyNewRooms(LegacyThirdPartyRulesTestModule):
-    def __init__(self, config: Dict, module_api: "ModuleApi"):
+    def __init__(self, config: Dict, module_api: "ModuleApi") -> None:
         super().__init__(config, module_api)
 
-    def on_create_room(
+    async def on_create_room(
         self, requester: Requester, config: dict, is_requester_admin: bool
-    ):
+    ) -> bool:
         return False
 
 
 class LegacyChangeEvents(LegacyThirdPartyRulesTestModule):
-    def __init__(self, config: Dict, module_api: "ModuleApi"):
+    def __init__(self, config: Dict, module_api: "ModuleApi") -> None:
         super().__init__(config, module_api)
 
-    async def check_event_allowed(self, event: EventBase, state: StateMap[EventBase]):
+    async def check_event_allowed(
+        self, event: EventBase, state: StateMap[EventBase]
+    ) -> JsonDict:
         d = event.get_dict()
         content = unfreeze(event.content)
         content["foo"] = "bar"
@@ -84,7 +94,7 @@ class ThirdPartyRulesTestCase(unittest.FederatingHomeserverTestCase):
         account.register_servlets,
     ]
 
-    def make_homeserver(self, reactor, clock):
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
         hs = self.setup_test_homeserver()
 
         load_legacy_third_party_event_rules(hs)
@@ -94,22 +104,30 @@ def make_homeserver(self, reactor, clock):
         # Note that these checks are not relevant to this test case.
 
         # Have this homeserver auto-approve all event signature checking.
-        async def approve_all_signature_checking(_, pdu):
+        async def approve_all_signature_checking(
+            _: RoomVersion, pdu: EventBase
+        ) -> EventBase:
             return pdu
 
-        hs.get_federation_server()._check_sigs_and_hash = approve_all_signature_checking
+        hs.get_federation_server()._check_sigs_and_hash = approve_all_signature_checking  # type: ignore[assignment]
 
         # Have this homeserver skip event auth checks. This is necessary due to
         # event auth checks ensuring that events were signed by the sender's homeserver.
-        async def _check_event_auth(origin, event, context, *args, **kwargs):
+        async def _check_event_auth(
+            origin: str,
+            event: EventBase,
+            context: EventContext,
+            *args: Any,
+            **kwargs: Any,
+        ) -> EventContext:
             return context
 
-        hs.get_federation_event_handler()._check_event_auth = _check_event_auth
+        hs.get_federation_event_handler()._check_event_auth = _check_event_auth  # type: ignore[assignment]
 
         return hs
 
-    def prepare(self, reactor, clock, homeserver):
-        super().prepare(reactor, clock, homeserver)
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        super().prepare(reactor, clock, hs)
         # Create some users and a room to play with during the tests
         self.user_id = self.register_user("kermit", "monkey")
         self.invitee = self.register_user("invitee", "hackme")
@@ -121,13 +139,15 @@ def prepare(self, reactor, clock, homeserver):
         except Exception:
             pass
 
-    def test_third_party_rules(self):
+    def test_third_party_rules(self) -> None:
         """Tests that a forbidden event is forbidden from being sent, but an allowed one
         can be sent.
         """
         # patch the rules module with a Mock which will return False for some event
         # types
-        async def check(ev, state):
+        async def check(
+            ev: EventBase, state: StateMap[EventBase]
+        ) -> Tuple[bool, Optional[JsonDict]]:
             return ev.type != "foo.bar.forbidden", None
 
         callback = Mock(spec=[], side_effect=check)
@@ -161,7 +181,7 @@ async def check(ev, state):
         )
         self.assertEqual(channel.result["code"], b"403", channel.result)
 
-    def test_third_party_rules_workaround_synapse_errors_pass_through(self):
+    def test_third_party_rules_workaround_synapse_errors_pass_through(self) -> None:
         """
         Tests that the workaround introduced by https://github.com/matrix-org/synapse/pull/11042
         is functional: that SynapseErrors are passed through from check_event_allowed
@@ -172,7 +192,7 @@ def test_third_party_rules_workaround_synapse_errors_pass_through(self):
         """
 
         class NastyHackException(SynapseError):
-            def error_dict(self):
+            def error_dict(self) -> JsonDict:
                 """
                 This overrides SynapseError's `error_dict` to nastily inject
                 JSON into the error response.
@@ -182,7 +202,9 @@ def error_dict(self):
                 return result
 
         # add a callback that will raise our hacky exception
-        async def check(ev, state) -> Tuple[bool, Optional[JsonDict]]:
+        async def check(
+            ev: EventBase, state: StateMap[EventBase]
+        ) -> Tuple[bool, Optional[JsonDict]]:
             raise NastyHackException(429, "message")
 
         self.hs.get_third_party_event_rules()._check_event_allowed_callbacks = [check]
@@ -202,11 +224,13 @@ async def check(ev, state) -> Tuple[bool, Optional[JsonDict]]:
             {"errcode": "M_UNKNOWN", "error": "message", "nasty": "very"},
         )
 
-    def test_cannot_modify_event(self):
+    def test_cannot_modify_event(self) -> None:
         """cannot accidentally modify an event before it is persisted"""
 
         # first patch the event checker so that it will try to modify the event
-        async def check(ev: EventBase, state):
+        async def check(
+            ev: EventBase, state: StateMap[EventBase]
+        ) -> Tuple[bool, Optional[JsonDict]]:
             ev.content = {"x": "y"}
             return True, None
 
@@ -223,10 +247,12 @@ async def check(ev: EventBase, state):
         # 500 Internal Server Error
         self.assertEqual(channel.code, 500, channel.result)
 
-    def test_modify_event(self):
+    def test_modify_event(self) -> None:
         """The module can return a modified version of the event"""
         # first patch the event checker so that it will modify the event
-        async def check(ev: EventBase, state):
+        async def check(
+            ev: EventBase, state: StateMap[EventBase]
+        ) -> Tuple[bool, Optional[JsonDict]]:
             d = ev.get_dict()
             d["content"] = {"x": "y"}
             return True, d
@@ -253,10 +279,12 @@ async def check(ev: EventBase, state):
         ev = channel.json_body
         self.assertEqual(ev["content"]["x"], "y")
 
-    def test_message_edit(self):
+    def test_message_edit(self) -> None:
         """Ensure that the module doesn't cause issues with edited messages."""
         # first patch the event checker so that it will modify the event
-        async def check(ev: EventBase, state):
+        async def check(
+            ev: EventBase, state: StateMap[EventBase]
+        ) -> Tuple[bool, Optional[JsonDict]]:
             d = ev.get_dict()
             d["content"] = {
                 "msgtype": "m.text",
@@ -315,7 +343,7 @@ async def check(ev: EventBase, state):
         ev = channel.json_body
         self.assertEqual(ev["content"]["body"], "EDITED BODY")
 
-    def test_send_event(self):
+    def test_send_event(self) -> None:
         """Tests that a module can send an event into a room via the module api"""
         content = {
             "msgtype": "m.text",
@@ -344,7 +372,7 @@ def test_send_event(self):
             }
         }
     )
-    def test_legacy_check_event_allowed(self):
+    def test_legacy_check_event_allowed(self) -> None:
         """Tests that the wrapper for legacy check_event_allowed callbacks works
         correctly.
         """
@@ -379,13 +407,13 @@ def test_legacy_check_event_allowed(self):
             }
         }
     )
-    def test_legacy_on_create_room(self):
+    def test_legacy_on_create_room(self) -> None:
         """Tests that the wrapper for legacy on_create_room callbacks works
         correctly.
         """
         self.helper.create_room_as(self.user_id, tok=self.tok, expect_code=403)
 
-    def test_sent_event_end_up_in_room_state(self):
+    def test_sent_event_end_up_in_room_state(self) -> None:
         """Tests that a state event sent by a module while processing another state event
         doesn't get dropped from the state of the room. This is to guard against a bug
         where Synapse has been observed doing so, see https://github.com/matrix-org/synapse/issues/10830
@@ -400,7 +428,9 @@ def test_sent_event_end_up_in_room_state(self):
         api = self.hs.get_module_api()
 
         # Define a callback that sends a custom event on power levels update.
-        async def test_fn(event: EventBase, state_events):
+        async def test_fn(
+            event: EventBase, state_events: StateMap[EventBase]
+        ) -> Tuple[bool, Optional[JsonDict]]:
             if event.is_state and event.type == EventTypes.PowerLevels:
                 await api.create_and_send_event_into_room(
                     {
@@ -436,7 +466,7 @@ async def test_fn(event: EventBase, state_events):
             self.assertEqual(channel.code, 200)
             self.assertEqual(channel.json_body["i"], i)
 
-    def test_on_new_event(self):
+    def test_on_new_event(self) -> None:
         """Test that the on_new_event callback is called on new events"""
         on_new_event = Mock(make_awaitable(None))
         self.hs.get_third_party_event_rules()._on_new_event_callbacks.append(
@@ -501,7 +531,7 @@ def _send_event_over_federation(self) -> None:
 
         self.assertEqual(channel.code, 200, channel.result)
 
-    def _update_power_levels(self, event_default: int = 0):
+    def _update_power_levels(self, event_default: int = 0) -> None:
         """Updates the room's power levels.
 
         Args:
@@ -533,7 +563,7 @@ def _update_power_levels(self, event_default: int = 0):
             tok=self.tok,
         )
 
-    def test_on_profile_update(self):
+    def test_on_profile_update(self) -> None:
         """Tests that the on_profile_update module callback is correctly called on
         profile updates.
         """
@@ -592,7 +622,7 @@ def test_on_profile_update(self):
         self.assertEqual(profile_info.display_name, displayname)
         self.assertEqual(profile_info.avatar_url, avatar_url)
 
-    def test_on_profile_update_admin(self):
+    def test_on_profile_update_admin(self) -> None:
         """Tests that the on_profile_update module callback is correctly called on
         profile updates triggered by a server admin.
         """
@@ -634,7 +664,7 @@ def test_on_profile_update_admin(self):
         self.assertEqual(profile_info.display_name, displayname)
         self.assertEqual(profile_info.avatar_url, avatar_url)
 
-    def test_on_user_deactivation_status_changed(self):
+    def test_on_user_deactivation_status_changed(self) -> None:
         """Tests that the on_user_deactivation_status_changed module callback is called
         correctly when processing a user's deactivation.
         """
@@ -691,7 +721,7 @@ def test_on_user_deactivation_status_changed(self):
         args = profile_mock.call_args[0]
         self.assertTrue(args[3])
 
-    def test_on_user_deactivation_status_changed_admin(self):
+    def test_on_user_deactivation_status_changed_admin(self) -> None:
         """Tests that the on_user_deactivation_status_changed module callback is called
         correctly when processing a user's deactivation triggered by a server admin as
         well as a reactivation.
@@ -745,3 +775,124 @@ def test_on_user_deactivation_status_changed_admin(self):
         self.assertEqual(args[0], user_id)
         self.assertFalse(args[1])
         self.assertTrue(args[2])
+
+    def test_check_can_deactivate_user(self) -> None:
+        """Tests that the on_user_deactivation_status_changed module callback is called
+        correctly when processing a user's deactivation.
+        """
+        # Register a mocked callback.
+        deactivation_mock = Mock(return_value=make_awaitable(False))
+        third_party_rules = self.hs.get_third_party_event_rules()
+        third_party_rules._check_can_deactivate_user_callbacks.append(
+            deactivation_mock,
+        )
+
+        # Register a user that we'll deactivate.
+        user_id = self.register_user("altan", "password")
+        tok = self.login("altan", "password")
+
+        # Deactivate that user.
+        channel = self.make_request(
+            "POST",
+            "/_matrix/client/v3/account/deactivate",
+            {
+                "auth": {
+                    "type": LoginType.PASSWORD,
+                    "password": "password",
+                    "identifier": {
+                        "type": "m.id.user",
+                        "user": user_id,
+                    },
+                },
+                "erase": True,
+            },
+            access_token=tok,
+        )
+
+        # Check that the deactivation was blocked
+        self.assertEqual(channel.code, 403, channel.json_body)
+
+        # Check that the mock was called once.
+        deactivation_mock.assert_called_once()
+        args = deactivation_mock.call_args[0]
+
+        # Check that the mock was called with the right user ID
+        self.assertEqual(args[0], user_id)
+
+        # Check that the request was not made by an admin
+        self.assertEqual(args[1], False)
+
+    def test_check_can_deactivate_user_admin(self) -> None:
+        """Tests that the on_user_deactivation_status_changed module callback is called
+        correctly when processing a user's deactivation triggered by a server admin.
+        """
+        # Register a mocked callback.
+        deactivation_mock = Mock(return_value=make_awaitable(False))
+        third_party_rules = self.hs.get_third_party_event_rules()
+        third_party_rules._check_can_deactivate_user_callbacks.append(
+            deactivation_mock,
+        )
+
+        # Register an admin user.
+        self.register_user("admin", "password", admin=True)
+        admin_tok = self.login("admin", "password")
+
+        # Register a user that we'll deactivate.
+        user_id = self.register_user("altan", "password")
+
+        # Deactivate the user.
+        channel = self.make_request(
+            "PUT",
+            "/_synapse/admin/v2/users/%s" % user_id,
+            {"deactivated": True},
+            access_token=admin_tok,
+        )
+
+        # Check that the deactivation was blocked
+        self.assertEqual(channel.code, 403, channel.json_body)
+
+        # Check that the mock was called once.
+        deactivation_mock.assert_called_once()
+        args = deactivation_mock.call_args[0]
+
+        # Check that the mock was called with the right user ID
+        self.assertEqual(args[0], user_id)
+
+        # Check that the mock was made by an admin
+        self.assertEqual(args[1], True)
+
+    def test_check_can_shutdown_room(self) -> None:
+        """Tests that the check_can_shutdown_room module callback is called
+        correctly when processing an admin's shutdown room request.
+        """
+        # Register a mocked callback.
+        shutdown_mock = Mock(return_value=make_awaitable(False))
+        third_party_rules = self.hs.get_third_party_event_rules()
+        third_party_rules._check_can_shutdown_room_callbacks.append(
+            shutdown_mock,
+        )
+
+        # Register an admin user.
+        admin_user_id = self.register_user("admin", "password", admin=True)
+        admin_tok = self.login("admin", "password")
+
+        # Shutdown the room.
+        channel = self.make_request(
+            "DELETE",
+            "/_synapse/admin/v2/rooms/%s" % self.room_id,
+            {},
+            access_token=admin_tok,
+        )
+
+        # Check that the shutdown was blocked
+        self.assertEqual(channel.code, 403, channel.json_body)
+
+        # Check that the mock was called once.
+        shutdown_mock.assert_called_once()
+        args = shutdown_mock.call_args[0]
+
+        # Check that the mock was called with the right user ID
+        self.assertEqual(args[0], admin_user_id)
+
+        # Check that the mock was called with the right room ID
+        self.assertEqual(args[1], self.room_id)
diff --git a/tests/rest/client/test_transactions.py b/tests/rest/client/test_transactions.py
index 3b5747cb12b8..8d8251b2ac99 100644
--- a/tests/rest/client/test_transactions.py
+++ b/tests/rest/client/test_transactions.py
@@ -1,3 +1,18 @@
+# Copyright 2018-2021 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from http import HTTPStatus
 from unittest.mock import Mock, call
 
 from twisted.internet import defer, reactor
@@ -11,14 +26,14 @@
 
 
 class HttpTransactionCacheTestCase(unittest.TestCase):
-    def setUp(self):
+    def setUp(self) -> None:
         self.clock = MockClock()
         self.hs = Mock()
         self.hs.get_clock = Mock(return_value=self.clock)
         self.hs.get_auth = Mock()
         self.cache = HttpTransactionCache(self.hs)
 
-        self.mock_http_response = (200, "GOOD JOB!")
+        self.mock_http_response = (HTTPStatus.OK, "GOOD JOB!")
         self.mock_key = "foo"
 
     @defer.inlineCallbacks
diff --git a/tests/rest/client/test_typing.py b/tests/rest/client/test_typing.py
index 8b2da88e8a58..d6da510773af 100644
--- a/tests/rest/client/test_typing.py
+++ b/tests/rest/client/test_typing.py
@@ -15,10 +15,12 @@
 
 """Tests REST events for /rooms paths."""
 
-from unittest.mock import Mock
+from twisted.test.proto_helpers import MemoryReactor
 
 from synapse.rest.client import room
+from synapse.server import HomeServer
 from synapse.types import UserID
+from synapse.util import Clock
 
 from tests import unittest
 
@@ -33,40 +35,17 @@ class RoomTypingTestCase(unittest.HomeserverTestCase):
     user = UserID.from_string(user_id)
     servlets = [room.register_servlets]
 
-    def make_homeserver(self, reactor, clock):
-
-        hs = self.setup_test_homeserver(
-            "red",
-            federation_http_client=None,
-            federation_client=Mock(),
-        )
-
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
+        hs = self.setup_test_homeserver("red")
         self.event_source = hs.get_event_sources().sources.typing
-
-        hs.get_federation_handler = Mock()
-
-        async def get_user_by_access_token(token=None, allow_guest=False):
-            return {
-                "user": UserID.from_string(self.auth_user_id),
-                "token_id": 1,
-                "is_guest": False,
-            }
-
-        hs.get_auth().get_user_by_access_token = get_user_by_access_token
-
-        async def _insert_client_ip(*args, **kwargs):
-            return None
-
-        hs.get_datastores().main.insert_client_ip = _insert_client_ip
-
         return hs
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.room_id = self.helper.create_room_as(self.user_id)
         # Need another user to make notifications actually work
         self.helper.join(self.room_id, user="@jim:red")
 
-    def test_set_typing(self):
+    def test_set_typing(self) -> None:
         channel = self.make_request(
             "PUT",
             "/rooms/%s/typing/%s" % (self.room_id, self.user_id),
@@ -95,7 +74,7 @@ def test_set_typing(self):
             ],
         )
 
-    def test_set_not_typing(self):
+    def test_set_not_typing(self) -> None:
         channel = self.make_request(
             "PUT",
             "/rooms/%s/typing/%s" % (self.room_id, self.user_id),
@@ -103,7 +82,7 @@ def test_set_not_typing(self):
         )
         self.assertEqual(200, channel.code)
 
-    def test_typing_timeout(self):
+    def test_typing_timeout(self) -> None:
         channel = self.make_request(
             "PUT",
             "/rooms/%s/typing/%s" % (self.room_id, self.user_id),
diff --git a/tests/rest/key/v2/test_remote_key_resource.py b/tests/rest/key/v2/test_remote_key_resource.py
index 4672a6859684..978c252f8482 100644
--- a/tests/rest/key/v2/test_remote_key_resource.py
+++ b/tests/rest/key/v2/test_remote_key_resource.py
@@ -13,19 +13,24 @@
 # limitations under the License.
 import urllib.parse
 from io import BytesIO, StringIO
+from typing import Any, Dict, Optional, Union
 from unittest.mock import Mock
 
 import signedjson.key
 from canonicaljson import encode_canonical_json
-from nacl.signing import SigningKey
 from signedjson.sign import sign_json
+from signedjson.types import SigningKey
 
-from twisted.web.resource import NoResource
+from twisted.test.proto_helpers import MemoryReactor
+from twisted.web.resource import NoResource, Resource
 
 from synapse.crypto.keyring import PerspectivesKeyFetcher
 from synapse.http.site import SynapseRequest
 from synapse.rest.key.v2 import KeyApiV2Resource
+from synapse.server import HomeServer
 from synapse.storage.keys import FetchKeyResult
+from synapse.types import JsonDict
+from synapse.util import Clock
 from synapse.util.httpresourcetree import create_resource_tree
 from synapse.util.stringutils import random_string
 
@@ -35,11 +40,11 @@
 
 
 class BaseRemoteKeyResourceTestCase(unittest.HomeserverTestCase):
-    def make_homeserver(self, reactor, clock):
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
         self.http_client = Mock()
         return self.setup_test_homeserver(federation_http_client=self.http_client)
 
-    def create_test_resource(self):
+    def create_test_resource(self) -> Resource:
         return create_resource_tree(
             {"/_matrix/key/v2": KeyApiV2Resource(self.hs)}, root_resource=NoResource()
         )
@@ -51,7 +56,12 @@ def expect_outgoing_key_request(
         Tell the mock http client to expect an outgoing GET request for the given key
         """
 
-        async def get_json(destination, path, ignore_backoff=False, **kwargs):
+        async def get_json(
+            destination: str,
+            path: str,
+            ignore_backoff: bool = False,
+            **kwargs: Any,
+        ) -> Union[JsonDict, list]:
             self.assertTrue(ignore_backoff)
             self.assertEqual(destination, server_name)
             key_id = "%s:%s" % (signing_key.alg, signing_key.version)
@@ -84,7 +94,8 @@ def make_notary_request(self, server_name: str, key_id: str) -> dict:
         Checks that the response is a 200 and returns the decoded json body.
         """
         channel = FakeChannel(self.site, self.reactor)
-        req = SynapseRequest(channel, self.site)
+        # channel is a `FakeChannel` but `HTTPChannel` is expected
+        req = SynapseRequest(channel, self.site)  # type: ignore[arg-type]
         req.content = BytesIO(b"")
         req.requestReceived(
             b"GET",
@@ -97,7 +108,7 @@ def make_notary_request(self, server_name: str, key_id: str) -> dict:
         resp = channel.json_body
         return resp
 
-    def test_get_key(self):
+    def test_get_key(self) -> None:
         """Fetch a remote key"""
         SERVER_NAME = "remote.server"
         testkey = signedjson.key.generate_signing_key("ver1")
@@ -114,7 +125,7 @@ def test_get_key(self):
         self.assertIn(SERVER_NAME, keys[0]["signatures"])
         self.assertIn(self.hs.hostname, keys[0]["signatures"])
 
-    def test_get_own_key(self):
+    def test_get_own_key(self) -> None:
         """Fetch our own key"""
         testkey = signedjson.key.generate_signing_key("ver1")
         self.expect_outgoing_key_request(self.hs.hostname, testkey)
@@ -141,7 +152,7 @@ class EndToEndPerspectivesTests(BaseRemoteKeyResourceTestCase):
     endpoint, to check that the two implementations are compatible.
     """
 
-    def default_config(self):
+    def default_config(self) -> Dict[str, Any]:
         config = super().default_config()
 
         # replace the signing key with our own
@@ -152,7 +163,7 @@ def default_config(self):
 
         return config
 
-    def prepare(self, reactor, clock, homeserver):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         # make a second homeserver, configured to use the first one as a key notary
         self.http_client2 = Mock()
         config = default_config(name="keyclient")
@@ -175,7 +186,9 @@ def prepare(self, reactor, clock, homeserver):
 
         # wire up outbound POST /key/v2/query requests from hs2 so that they
         # will be forwarded to hs1
-        async def post_json(destination, path, data):
+        async def post_json(
+            destination: str, path: str, data: Optional[JsonDict] = None
+        ) -> Union[JsonDict, list]:
             self.assertEqual(destination, self.hs.hostname)
             self.assertEqual(
                 path,
@@ -183,7 +196,8 @@ async def post_json(destination, path, data):
             )
 
             channel = FakeChannel(self.site, self.reactor)
-            req = SynapseRequest(channel, self.site)
+            # channel is a `FakeChannel` but `HTTPChannel` is expected
+            req = SynapseRequest(channel, self.site)  # type: ignore[arg-type]
             req.content = BytesIO(encode_canonical_json(data))
 
             req.requestReceived(
@@ -198,7 +212,7 @@ async def post_json(destination, path, data):
 
         self.http_client2.post_json.side_effect = post_json
 
-    def test_get_key(self):
+    def test_get_key(self) -> None:
         """Fetch a key belonging to a random server"""
         # make up a key to be fetched.
         testkey = signedjson.key.generate_signing_key("abc")
@@ -218,7 +232,7 @@ def test_get_key(self):
             signedjson.key.encode_verify_key_base64(testkey.verify_key),
         )
 
-    def test_get_notary_key(self):
+    def test_get_notary_key(self) -> None:
         """Fetch a key belonging to the notary server"""
         # make up a key to be fetched. We randomise the keyid to try to get it to
         # appear before the key server signing key sometimes (otherwise we bail out
@@ -240,7 +254,7 @@ def test_get_notary_key(self):
             signedjson.key.encode_verify_key_base64(testkey.verify_key),
         )
 
-    def test_get_notary_keyserver_key(self):
+    def test_get_notary_keyserver_key(self) -> None:
         """Fetch the notary's keyserver key"""
         # we expect hs1 to make a regular key request to itself
         self.expect_outgoing_key_request(self.hs.hostname, self.hs_signing_key)
diff --git a/tests/rest/media/v1/test_base.py b/tests/rest/media/v1/test_base.py
index f761e23f1bf0..c73179151adb 100644
--- a/tests/rest/media/v1/test_base.py
+++ b/tests/rest/media/v1/test_base.py
@@ -28,11 +28,11 @@ class GetFileNameFromHeadersTests(unittest.TestCase):
         b"inline; filename*=utf-8''foo%C2%A3bar": "foo£bar",
     }
 
-    def tests(self):
+    def tests(self) -> None:
         for hdr, expected in self.TEST_CASES.items():
             res = get_filename_from_headers({b"Content-Disposition": [hdr]})
             self.assertEqual(
                 res,
                 expected,
-                "expected output for %s to be %s but was %s" % (hdr, expected, res),
+                f"expected output for {hdr!r} to be {expected} but was {res}",
             )
diff --git a/tests/rest/media/v1/test_filepath.py b/tests/rest/media/v1/test_filepath.py
index 913bc530aac1..43e6f0f70aad 100644
--- a/tests/rest/media/v1/test_filepath.py
+++ b/tests/rest/media/v1/test_filepath.py
@@ -21,12 +21,12 @@
 
 
 class MediaFilePathsTestCase(unittest.TestCase):
-    def setUp(self):
+    def setUp(self) -> None:
         super().setUp()
 
         self.filepaths = MediaFilePaths("/media_store")
 
-    def test_local_media_filepath(self):
+    def test_local_media_filepath(self) -> None:
         """Test local media paths"""
         self.assertEqual(
             self.filepaths.local_media_filepath_rel("GerZNDnDZVjsOtardLuwfIBg"),
@@ -37,7 +37,7 @@ def test_local_media_filepath(self):
             "/media_store/local_content/Ge/rZ/NDnDZVjsOtardLuwfIBg",
         )
 
-    def test_local_media_thumbnail(self):
+    def test_local_media_thumbnail(self) -> None:
         """Test local media thumbnail paths"""
         self.assertEqual(
             self.filepaths.local_media_thumbnail_rel(
@@ -52,14 +52,14 @@ def test_local_media_thumbnail(self):
             "/media_store/local_thumbnails/Ge/rZ/NDnDZVjsOtardLuwfIBg/800-600-image-jpeg-scale",
         )
 
-    def test_local_media_thumbnail_dir(self):
+    def test_local_media_thumbnail_dir(self) -> None:
         """Test local media thumbnail directory paths"""
         self.assertEqual(
             self.filepaths.local_media_thumbnail_dir("GerZNDnDZVjsOtardLuwfIBg"),
             "/media_store/local_thumbnails/Ge/rZ/NDnDZVjsOtardLuwfIBg",
         )
 
-    def test_remote_media_filepath(self):
+    def test_remote_media_filepath(self) -> None:
         """Test remote media paths"""
         self.assertEqual(
             self.filepaths.remote_media_filepath_rel(
@@ -74,7 +74,7 @@ def test_remote_media_filepath(self):
             "/media_store/remote_content/example.com/Ge/rZ/NDnDZVjsOtardLuwfIBg",
         )
 
-    def test_remote_media_thumbnail(self):
+    def test_remote_media_thumbnail(self) -> None:
         """Test remote media thumbnail paths"""
         self.assertEqual(
             self.filepaths.remote_media_thumbnail_rel(
@@ -99,7 +99,7 @@ def test_remote_media_thumbnail(self):
             "/media_store/remote_thumbnail/example.com/Ge/rZ/NDnDZVjsOtardLuwfIBg/800-600-image-jpeg-scale",
         )
 
-    def test_remote_media_thumbnail_legacy(self):
+    def test_remote_media_thumbnail_legacy(self) -> None:
         """Test old-style remote media thumbnail paths"""
         self.assertEqual(
             self.filepaths.remote_media_thumbnail_rel_legacy(
@@ -108,7 +108,7 @@ def test_remote_media_thumbnail_legacy(self):
             "remote_thumbnail/example.com/Ge/rZ/NDnDZVjsOtardLuwfIBg/800-600-image-jpeg",
         )
 
-    def test_remote_media_thumbnail_dir(self):
+    def test_remote_media_thumbnail_dir(self) -> None:
         """Test remote media thumbnail directory paths"""
         self.assertEqual(
             self.filepaths.remote_media_thumbnail_dir(
@@ -117,7 +117,7 @@ def test_remote_media_thumbnail_dir(self):
             "/media_store/remote_thumbnail/example.com/Ge/rZ/NDnDZVjsOtardLuwfIBg",
         )
 
-    def test_url_cache_filepath(self):
+    def test_url_cache_filepath(self) -> None:
         """Test URL cache paths"""
         self.assertEqual(
             self.filepaths.url_cache_filepath_rel("2020-01-02_GerZNDnDZVjsOtar"),
@@ -128,7 +128,7 @@ def test_url_cache_filepath(self):
             "/media_store/url_cache/2020-01-02/GerZNDnDZVjsOtar",
         )
 
-    def test_url_cache_filepath_legacy(self):
+    def test_url_cache_filepath_legacy(self) -> None:
         """Test old-style URL cache paths"""
         self.assertEqual(
             self.filepaths.url_cache_filepath_rel("GerZNDnDZVjsOtardLuwfIBg"),
@@ -139,7 +139,7 @@ def test_url_cache_filepath_legacy(self):
             "/media_store/url_cache/Ge/rZ/NDnDZVjsOtardLuwfIBg",
         )
 
-    def test_url_cache_filepath_dirs_to_delete(self):
+    def test_url_cache_filepath_dirs_to_delete(self) -> None:
         """Test URL cache cleanup paths"""
         self.assertEqual(
             self.filepaths.url_cache_filepath_dirs_to_delete(
@@ -148,7 +148,7 @@ def test_url_cache_filepath_dirs_to_delete(self):
             ["/media_store/url_cache/2020-01-02"],
         )
 
-    def test_url_cache_filepath_dirs_to_delete_legacy(self):
+    def test_url_cache_filepath_dirs_to_delete_legacy(self) -> None:
         """Test old-style URL cache cleanup paths"""
         self.assertEqual(
             self.filepaths.url_cache_filepath_dirs_to_delete(
@@ -160,7 +160,7 @@ def test_url_cache_filepath_dirs_to_delete_legacy(self):
             ],
         )
 
-    def test_url_cache_thumbnail(self):
+    def test_url_cache_thumbnail(self) -> None:
         """Test URL cache thumbnail paths"""
         self.assertEqual(
             self.filepaths.url_cache_thumbnail_rel(
@@ -175,7 +175,7 @@ def test_url_cache_thumbnail(self):
             "/media_store/url_cache_thumbnails/2020-01-02/GerZNDnDZVjsOtar/800-600-image-jpeg-scale",
         )
 
-    def test_url_cache_thumbnail_legacy(self):
+    def test_url_cache_thumbnail_legacy(self) -> None:
         """Test old-style URL cache thumbnail paths"""
         self.assertEqual(
             self.filepaths.url_cache_thumbnail_rel(
@@ -190,7 +190,7 @@ def test_url_cache_thumbnail_legacy(self):
             "/media_store/url_cache_thumbnails/Ge/rZ/NDnDZVjsOtardLuwfIBg/800-600-image-jpeg-scale",
         )
 
-    def test_url_cache_thumbnail_directory(self):
+    def test_url_cache_thumbnail_directory(self) -> None:
         """Test URL cache thumbnail directory paths"""
         self.assertEqual(
             self.filepaths.url_cache_thumbnail_directory_rel(
@@ -203,7 +203,7 @@ def test_url_cache_thumbnail_directory(self):
             "/media_store/url_cache_thumbnails/2020-01-02/GerZNDnDZVjsOtar",
         )
 
-    def test_url_cache_thumbnail_directory_legacy(self):
+    def test_url_cache_thumbnail_directory_legacy(self) -> None:
         """Test old-style URL cache thumbnail directory paths"""
         self.assertEqual(
             self.filepaths.url_cache_thumbnail_directory_rel(
@@ -216,7 +216,7 @@ def test_url_cache_thumbnail_directory_legacy(self):
             "/media_store/url_cache_thumbnails/Ge/rZ/NDnDZVjsOtardLuwfIBg",
         )
 
-    def test_url_cache_thumbnail_dirs_to_delete(self):
+    def test_url_cache_thumbnail_dirs_to_delete(self) -> None:
         """Test URL cache thumbnail cleanup paths"""
         self.assertEqual(
             self.filepaths.url_cache_thumbnail_dirs_to_delete(
@@ -228,7 +228,7 @@ def test_url_cache_thumbnail_dirs_to_delete(self):
             ],
         )
 
-    def test_url_cache_thumbnail_dirs_to_delete_legacy(self):
+    def test_url_cache_thumbnail_dirs_to_delete_legacy(self) -> None:
         """Test old-style URL cache thumbnail cleanup paths"""
         self.assertEqual(
             self.filepaths.url_cache_thumbnail_dirs_to_delete(
@@ -241,7 +241,7 @@ def test_url_cache_thumbnail_dirs_to_delete_legacy(self):
             ],
         )
 
-    def test_server_name_validation(self):
+    def test_server_name_validation(self) -> None:
         """Test validation of server names"""
         self._test_path_validation(
             [
@@ -274,7 +274,7 @@ def test_server_name_validation(self):
             ],
         )
 
-    def test_file_id_validation(self):
+    def test_file_id_validation(self) -> None:
         """Test validation of local, remote and legacy URL cache file / media IDs"""
         # File / media IDs get split into three parts to form paths, consisting of the
         # first two characters, next two characters and rest of the ID.
@@ -357,7 +357,7 @@ def test_file_id_validation(self):
             invalid_values=invalid_file_ids,
         )
 
-    def test_url_cache_media_id_validation(self):
+    def test_url_cache_media_id_validation(self) -> None:
         """Test validation of URL cache media IDs"""
         self._test_path_validation(
             [
@@ -387,7 +387,7 @@ def test_url_cache_media_id_validation(self):
             ],
         )
 
-    def test_content_type_validation(self):
+    def test_content_type_validation(self) -> None:
         """Test validation of thumbnail content types"""
         self._test_path_validation(
             [
@@ -410,7 +410,7 @@ def test_content_type_validation(self):
             ],
         )
 
-    def test_thumbnail_method_validation(self):
+    def test_thumbnail_method_validation(self) -> None:
         """Test validation of thumbnail methods"""
         self._test_path_validation(
             [
@@ -440,7 +440,7 @@ def _test_path_validation(
         parameter: str,
         valid_values: Iterable[str],
         invalid_values: Iterable[str],
-    ):
+    ) -> None:
         """Test that the specified methods validate the named parameter as expected
 
         Args:
diff --git a/tests/rest/media/v1/test_html_preview.py b/tests/rest/media/v1/test_html_preview.py
index a4b57e3d1feb..3fb37a2a5970 100644
--- a/tests/rest/media/v1/test_html_preview.py
+++ b/tests/rest/media/v1/test_html_preview.py
@@ -32,7 +32,7 @@ class SummarizeTestCase(unittest.TestCase):
     if not lxml:
         skip = "url preview feature requires lxml"
 
-    def test_long_summarize(self):
+    def test_long_summarize(self) -> None:
         example_paras = [
             """Tromsø (Norwegian pronunciation: [ˈtrʊmsœ] ( listen); Northern Sami:
             Romsa; Finnish: Tromssa[2] Kven: Tromssa) is a city and municipality in
@@ -90,7 +90,7 @@ def test_long_summarize(self):
             " Tromsøya had a population of 36,088. Substantial parts of the urban…",
         )
 
-    def test_short_summarize(self):
+    def test_short_summarize(self) -> None:
         example_paras = [
             "Tromsø (Norwegian pronunciation: [ˈtrʊmsœ] ( listen); Northern Sami:"
             " Romsa; Finnish: Tromssa[2] Kven: Tromssa) is a city and municipality in"
@@ -117,7 +117,7 @@ def test_short_summarize(self):
             " most of the year.",
         )
 
-    def test_small_then_large_summarize(self):
+    def test_small_then_large_summarize(self) -> None:
         example_paras = [
             "Tromsø (Norwegian pronunciation: [ˈtrʊmsœ] ( listen); Northern Sami:"
             " Romsa; Finnish: Tromssa[2] Kven: Tromssa) is a city and municipality in"
@@ -150,7 +150,7 @@ class CalcOgTestCase(unittest.TestCase):
     if not lxml:
         skip = "url preview feature requires lxml"
 
-    def test_simple(self):
+    def test_simple(self) -> None:
         html = b"""
         <html>
         <head><title>Foo</title></head>
@@ -165,7 +165,7 @@ def test_simple(self):
 
         self.assertEqual(og, {"og:title": "Foo", "og:description": "Some text."})
 
-    def test_comment(self):
+    def test_comment(self) -> None:
         html = b"""
         <html>
         <head><title>Foo</title></head>
@@ -181,7 +181,7 @@ def test_comment(self):
 
         self.assertEqual(og, {"og:title": "Foo", "og:description": "Some text."})
 
-    def test_comment2(self):
+    def test_comment2(self) -> None:
         html = b"""
         <html>
         <head><title>Foo</title></head>
@@ -206,7 +206,7 @@ def test_comment2(self):
             },
         )
 
-    def test_script(self):
+    def test_script(self) -> None:
         html = b"""
         <html>
         <head><title>Foo</title></head>
@@ -222,7 +222,7 @@ def test_script(self):
 
         self.assertEqual(og, {"og:title": "Foo", "og:description": "Some text."})
 
-    def test_missing_title(self):
+    def test_missing_title(self) -> None:
         html = b"""
         <html>
         <body>
@@ -236,7 +236,7 @@ def test_missing_title(self):
 
         self.assertEqual(og, {"og:title": None, "og:description": "Some text."})
 
-    def test_h1_as_title(self):
+    def test_h1_as_title(self) -> None:
         html = b"""
         <html>
         <meta property="og:description" content="Some text."/>
@@ -251,7 +251,7 @@ def test_h1_as_title(self):
 
         self.assertEqual(og, {"og:title": "Title", "og:description": "Some text."})
 
-    def test_missing_title_and_broken_h1(self):
+    def test_missing_title_and_broken_h1(self) -> None:
         html = b"""
         <html>
         <body>
@@ -266,19 +266,19 @@ def test_missing_title_and_broken_h1(self):
 
         self.assertEqual(og, {"og:title": None, "og:description": "Some text."})
 
-    def test_empty(self):
+    def test_empty(self) -> None:
         """Test a body with no data in it."""
         html = b""
         tree = decode_body(html, "http://example.com/test.html")
         self.assertIsNone(tree)
 
-    def test_no_tree(self):
+    def test_no_tree(self) -> None:
         """A valid body with no tree in it."""
         html = b"\x00"
         tree = decode_body(html, "http://example.com/test.html")
         self.assertIsNone(tree)
 
-    def test_xml(self):
+    def test_xml(self) -> None:
         """Test decoding XML and ensure it works properly."""
         # Note that the strip() call is important to ensure the xml tag starts
         # at the initial byte.
@@ -293,7 +293,7 @@ def test_xml(self):
         og = parse_html_to_open_graph(tree, "http://example.com/test.html")
         self.assertEqual(og, {"og:title": "Foo", "og:description": "Some text."})
 
-    def test_invalid_encoding(self):
+    def test_invalid_encoding(self) -> None:
         """An invalid character encoding should be ignored and treated as UTF-8, if possible."""
         html = b"""
         <html>
@@ -307,7 +307,7 @@ def test_invalid_encoding(self):
         og = parse_html_to_open_graph(tree, "http://example.com/test.html")
         self.assertEqual(og, {"og:title": "Foo", "og:description": "Some text."})
 
-    def test_invalid_encoding2(self):
+    def test_invalid_encoding2(self) -> None:
         """A body which doesn't match the sent character encoding."""
         # Note that this contains an invalid UTF-8 sequence in the title.
         html = b"""
@@ -322,7 +322,7 @@ def test_invalid_encoding2(self):
         og = parse_html_to_open_graph(tree, "http://example.com/test.html")
         self.assertEqual(og, {"og:title": "ÿÿ Foo", "og:description": "Some text."})
 
-    def test_windows_1252(self):
+    def test_windows_1252(self) -> None:
         """A body which uses cp1252, but doesn't declare that."""
         html = b"""
         <html>
@@ -338,7 +338,7 @@ def test_windows_1252(self):
 
 
 class MediaEncodingTestCase(unittest.TestCase):
-    def test_meta_charset(self):
+    def test_meta_charset(self) -> None:
         """A character encoding is found via the meta tag."""
         encodings = _get_html_media_encodings(
             b"""
@@ -363,7 +363,7 @@ def test_meta_charset(self):
         )
         self.assertEqual(list(encodings), ["ascii", "utf-8", "cp1252"])
 
-    def test_meta_charset_underscores(self):
+    def test_meta_charset_underscores(self) -> None:
         """A character encoding contains underscore."""
         encodings = _get_html_media_encodings(
             b"""
@@ -376,7 +376,7 @@ def test_meta_charset_underscores(self):
         )
         self.assertEqual(list(encodings), ["shift_jis", "utf-8", "cp1252"])
 
-    def test_xml_encoding(self):
+    def test_xml_encoding(self) -> None:
         """A character encoding is found via the meta tag."""
         encodings = _get_html_media_encodings(
             b"""
@@ -388,7 +388,7 @@ def test_xml_encoding(self):
         )
         self.assertEqual(list(encodings), ["ascii", "utf-8", "cp1252"])
 
-    def test_meta_xml_encoding(self):
+    def test_meta_xml_encoding(self) -> None:
         """Meta tags take precedence over XML encoding."""
         encodings = _get_html_media_encodings(
             b"""
@@ -402,7 +402,7 @@ def test_meta_xml_encoding(self):
         )
         self.assertEqual(list(encodings), ["utf-16", "ascii", "utf-8", "cp1252"])
 
-    def test_content_type(self):
+    def test_content_type(self) -> None:
         """A character encoding is found via the Content-Type header."""
         # Test a few variations of the header.
         headers = (
@@ -417,12 +417,12 @@ def test_content_type(self):
             encodings = _get_html_media_encodings(b"", header)
             self.assertEqual(list(encodings), ["ascii", "utf-8", "cp1252"])
 
-    def test_fallback(self):
+    def test_fallback(self) -> None:
         """A character encoding cannot be found in the body or header."""
         encodings = _get_html_media_encodings(b"", "text/html")
         self.assertEqual(list(encodings), ["utf-8", "cp1252"])
 
-    def test_duplicates(self):
+    def test_duplicates(self) -> None:
         """Ensure each encoding is only attempted once."""
         encodings = _get_html_media_encodings(
             b"""
@@ -436,7 +436,7 @@ def test_duplicates(self):
         )
         self.assertEqual(list(encodings), ["utf-8", "cp1252"])
 
-    def test_unknown_invalid(self):
+    def test_unknown_invalid(self) -> None:
         """A character encoding should be ignored if it is unknown or invalid."""
         encodings = _get_html_media_encodings(
             b"""
@@ -451,7 +451,7 @@ def test_unknown_invalid(self):
 
 
 class RebaseUrlTestCase(unittest.TestCase):
-    def test_relative(self):
+    def test_relative(self) -> None:
         """Relative URLs should be resolved based on the context of the base URL."""
         self.assertEqual(
             rebase_url("subpage", "https://example.com/foo/"),
@@ -466,14 +466,14 @@ def test_relative(self):
             "https://example.com/bar",
         )
 
-    def test_absolute(self):
+    def test_absolute(self) -> None:
         """Absolute URLs should not be modified."""
         self.assertEqual(
             rebase_url("https://alice.com/a/", "https://example.com/foo/"),
             "https://alice.com/a/",
         )
 
-    def test_data(self):
+    def test_data(self) -> None:
         """Data URLs should not be modified."""
         self.assertEqual(
             rebase_url("data:,Hello%2C%20World%21", "https://example.com/foo/"),
diff --git a/tests/rest/media/v1/test_media_storage.py b/tests/rest/media/v1/test_media_storage.py
index cba9be17c4ca..7204b2dfe075 100644
--- a/tests/rest/media/v1/test_media_storage.py
+++ b/tests/rest/media/v1/test_media_storage.py
@@ -16,7 +16,7 @@
 import tempfile
 from binascii import unhexlify
 from io import BytesIO
-from typing import Optional
+from typing import Any, BinaryIO, Dict, List, Optional, Union
 from unittest.mock import Mock
 from urllib import parse
 
@@ -26,18 +26,24 @@
 
 from twisted.internet import defer
 from twisted.internet.defer import Deferred
+from twisted.test.proto_helpers import MemoryReactor
 
+from synapse.events import EventBase
 from synapse.events.spamcheck import load_legacy_spam_checkers
 from synapse.logging.context import make_deferred_yieldable
+from synapse.module_api import ModuleApi
 from synapse.rest import admin
 from synapse.rest.client import login
 from synapse.rest.media.v1._base import FileInfo
 from synapse.rest.media.v1.filepath import MediaFilePaths
-from synapse.rest.media.v1.media_storage import MediaStorage
+from synapse.rest.media.v1.media_storage import MediaStorage, ReadableFileWrapper
 from synapse.rest.media.v1.storage_provider import FileStorageProviderBackend
+from synapse.server import HomeServer
+from synapse.types import RoomAlias
+from synapse.util import Clock
 
 from tests import unittest
-from tests.server import FakeSite, make_request
+from tests.server import FakeChannel, FakeSite, make_request
 from tests.test_utils import SMALL_PNG
 from tests.utils import default_config
 
@@ -46,7 +52,7 @@ class MediaStorageTests(unittest.HomeserverTestCase):
 
     needs_threadpool = True
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.test_dir = tempfile.mkdtemp(prefix="synapse-tests-")
         self.addCleanup(shutil.rmtree, self.test_dir)
 
@@ -62,7 +68,7 @@ def prepare(self, reactor, clock, hs):
             hs, self.primary_base_path, self.filepaths, storage_providers
         )
 
-    def test_ensure_media_is_in_local_cache(self):
+    def test_ensure_media_is_in_local_cache(self) -> None:
         media_id = "some_media_id"
         test_body = "Test\n"
 
@@ -105,7 +111,7 @@ def test_ensure_media_is_in_local_cache(self):
         self.assertEqual(test_body, body)
 
 
-@attr.s(slots=True, frozen=True)
+@attr.s(auto_attribs=True, slots=True, frozen=True)
 class _TestImage:
     """An image for testing thumbnailing with the expected results
 
@@ -121,18 +127,18 @@ class _TestImage:
             a 404 is expected.
     """
 
-    data = attr.ib(type=bytes)
-    content_type = attr.ib(type=bytes)
-    extension = attr.ib(type=bytes)
-    expected_cropped = attr.ib(type=Optional[bytes], default=None)
-    expected_scaled = attr.ib(type=Optional[bytes], default=None)
-    expected_found = attr.ib(default=True, type=bool)
+    data: bytes
+    content_type: bytes
+    extension: bytes
+    expected_cropped: Optional[bytes] = None
+    expected_scaled: Optional[bytes] = None
+    expected_found: bool = True
 
 
 @parameterized_class(
     ("test_image",),
     [
-        # smoll png
+        # small png
         (
             _TestImage(
                 SMALL_PNG,
@@ -193,11 +199,17 @@ class MediaRepoTests(unittest.HomeserverTestCase):
     hijack_auth = True
     user_id = "@test:user"
 
-    def make_homeserver(self, reactor, clock):
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
 
         self.fetches = []
 
-        def get_file(destination, path, output_stream, args=None, max_size=None):
+        def get_file(
+            destination: str,
+            path: str,
+            output_stream: BinaryIO,
+            args: Optional[Dict[str, Union[str, List[str]]]] = None,
+            max_size: Optional[int] = None,
+        ) -> Deferred:
             """
             Returns tuple[int,dict,str,int] of file length, response headers,
             absolute URI, and response code.
@@ -238,7 +250,7 @@ def write_to(r):
 
         return hs
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
 
         media_resource = hs.get_media_repository_resource()
         self.download_resource = media_resource.children[b"download"]
@@ -248,8 +260,9 @@ def prepare(self, reactor, clock, hs):
 
         self.media_id = "example.com/12345"
 
-    def _req(self, content_disposition, include_content_type=True):
-
+    def _req(
+        self, content_disposition: Optional[bytes], include_content_type: bool = True
+    ) -> FakeChannel:
         channel = make_request(
             self.reactor,
             FakeSite(self.download_resource, self.reactor),
@@ -288,7 +301,7 @@ def _req(self, content_disposition, include_content_type=True):
 
         return channel
 
-    def test_handle_missing_content_type(self):
+    def test_handle_missing_content_type(self) -> None:
         channel = self._req(
             b"inline; filename=out" + self.test_image.extension,
             include_content_type=False,
@@ -299,7 +312,7 @@ def test_handle_missing_content_type(self):
             headers.getRawHeaders(b"Content-Type"), [b"application/octet-stream"]
         )
 
-    def test_disposition_filename_ascii(self):
+    def test_disposition_filename_ascii(self) -> None:
         """
         If the filename is filename=<ascii> then Synapse will decode it as an
         ASCII string, and use filename= in the response.
@@ -315,7 +328,7 @@ def test_disposition_filename_ascii(self):
             [b"inline; filename=out" + self.test_image.extension],
         )
 
-    def test_disposition_filenamestar_utf8escaped(self):
+    def test_disposition_filenamestar_utf8escaped(self) -> None:
         """
         If the filename is filename=*utf8''<utf8 escaped> then Synapse will
         correctly decode it as the UTF-8 string, and use filename* in the
@@ -335,7 +348,7 @@ def test_disposition_filenamestar_utf8escaped(self):
             [b"inline; filename*=utf-8''" + filename + self.test_image.extension],
         )
 
-    def test_disposition_none(self):
+    def test_disposition_none(self) -> None:
         """
         If there is no filename, one isn't passed on in the Content-Disposition
         of the request.
@@ -348,26 +361,26 @@ def test_disposition_none(self):
         )
         self.assertEqual(headers.getRawHeaders(b"Content-Disposition"), None)
 
-    def test_thumbnail_crop(self):
+    def test_thumbnail_crop(self) -> None:
         """Test that a cropped remote thumbnail is available."""
         self._test_thumbnail(
             "crop", self.test_image.expected_cropped, self.test_image.expected_found
         )
 
-    def test_thumbnail_scale(self):
+    def test_thumbnail_scale(self) -> None:
         """Test that a scaled remote thumbnail is available."""
         self._test_thumbnail(
             "scale", self.test_image.expected_scaled, self.test_image.expected_found
         )
 
-    def test_invalid_type(self):
+    def test_invalid_type(self) -> None:
         """An invalid thumbnail type is never available."""
         self._test_thumbnail("invalid", None, False)
 
     @unittest.override_config(
         {"thumbnail_sizes": [{"width": 32, "height": 32, "method": "scale"}]}
     )
-    def test_no_thumbnail_crop(self):
+    def test_no_thumbnail_crop(self) -> None:
         """
         Override the config to generate only scaled thumbnails, but request a cropped one.
         """
@@ -376,13 +389,13 @@ def test_no_thumbnail_crop(self):
     @unittest.override_config(
         {"thumbnail_sizes": [{"width": 32, "height": 32, "method": "crop"}]}
     )
-    def test_no_thumbnail_scale(self):
+    def test_no_thumbnail_scale(self) -> None:
         """
         Override the config to generate only cropped thumbnails, but request a scaled one.
         """
         self._test_thumbnail("scale", None, False)
 
-    def test_thumbnail_repeated_thumbnail(self):
+    def test_thumbnail_repeated_thumbnail(self) -> None:
         """Test that fetching the same thumbnail works, and deleting the on disk
         thumbnail regenerates it.
         """
@@ -443,7 +456,9 @@ def test_thumbnail_repeated_thumbnail(self):
                 channel.result["body"],
             )
 
-    def _test_thumbnail(self, method, expected_body, expected_found):
+    def _test_thumbnail(
+        self, method: str, expected_body: Optional[bytes], expected_found: bool
+    ) -> None:
         params = "?width=32&height=32&method=" + method
         channel = make_request(
             self.reactor,
@@ -485,7 +500,7 @@ def _test_thumbnail(self, method, expected_body, expected_found):
             )
 
     @parameterized.expand([("crop", 16), ("crop", 64), ("scale", 16), ("scale", 64)])
-    def test_same_quality(self, method, desired_size):
+    def test_same_quality(self, method: str, desired_size: int) -> None:
         """Test that choosing between thumbnails with the same quality rating succeeds.
 
         We are not particular about which thumbnail is chosen."""
@@ -521,7 +536,7 @@ def test_same_quality(self, method, desired_size):
             )
         )
 
-    def test_x_robots_tag_header(self):
+    def test_x_robots_tag_header(self) -> None:
         """
         Tests that the `X-Robots-Tag` header is present, which informs web crawlers
         to not index, archive, or follow links in media.
@@ -540,29 +555,38 @@ class TestSpamChecker:
     `evil`.
     """
 
-    def __init__(self, config, api):
+    def __init__(self, config: Dict[str, Any], api: ModuleApi) -> None:
         self.config = config
         self.api = api
 
-    def parse_config(config):
+    def parse_config(config: Dict[str, Any]) -> Dict[str, Any]:
         return config
 
-    async def check_event_for_spam(self, foo):
+    async def check_event_for_spam(self, event: EventBase) -> Union[bool, str]:
         return False  # allow all events
 
-    async def user_may_invite(self, inviter_userid, invitee_userid, room_id):
+    async def user_may_invite(
+        self,
+        inviter_userid: str,
+        invitee_userid: str,
+        room_id: str,
+    ) -> bool:
         return True  # allow all invites
 
-    async def user_may_create_room(self, userid):
+    async def user_may_create_room(self, userid: str) -> bool:
         return True  # allow all room creations
 
-    async def user_may_create_room_alias(self, userid, room_alias):
+    async def user_may_create_room_alias(
+        self, userid: str, room_alias: RoomAlias
+    ) -> bool:
         return True  # allow all room aliases
 
-    async def user_may_publish_room(self, userid, room_id):
+    async def user_may_publish_room(self, userid: str, room_id: str) -> bool:
         return True  # allow publishing of all rooms
 
-    async def check_media_file_for_spam(self, file_wrapper, file_info) -> bool:
+    async def check_media_file_for_spam(
+        self, file_wrapper: ReadableFileWrapper, file_info: FileInfo
+    ) -> bool:
         buf = BytesIO()
         await file_wrapper.write_chunks_to(buf.write)
 
@@ -575,7 +599,7 @@ class SpamCheckerTestCase(unittest.HomeserverTestCase):
         admin.register_servlets,
     ]
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.user = self.register_user("user", "pass")
         self.tok = self.login("user", "pass")
 
@@ -586,7 +610,7 @@ def prepare(self, reactor, clock, hs):
 
         load_legacy_spam_checkers(hs)
 
-    def default_config(self):
+    def default_config(self) -> Dict[str, Any]:
         config = default_config("test")
 
         config.update(
@@ -602,13 +626,13 @@ def default_config(self):
 
         return config
 
-    def test_upload_innocent(self):
+    def test_upload_innocent(self) -> None:
         """Attempt to upload some innocent data that should be allowed."""
         self.helper.upload_media(
             self.upload_resource, SMALL_PNG, tok=self.tok, expect_code=200
         )
 
-    def test_upload_ban(self):
+    def test_upload_ban(self) -> None:
         """Attempt to upload some data that includes bytes "evil", which should
         get rejected by the spam checker.
         """
diff --git a/tests/rest/media/v1/test_oembed.py b/tests/rest/media/v1/test_oembed.py
index 048d0ca44a95..f38d7225f8f6 100644
--- a/tests/rest/media/v1/test_oembed.py
+++ b/tests/rest/media/v1/test_oembed.py
@@ -16,7 +16,7 @@
 
 from twisted.test.proto_helpers import MemoryReactor
 
-from synapse.rest.media.v1.oembed import OEmbedProvider
+from synapse.rest.media.v1.oembed import OEmbedProvider, OEmbedResult
 from synapse.server import HomeServer
 from synapse.types import JsonDict
 from synapse.util import Clock
@@ -25,15 +25,15 @@
 
 
 class OEmbedTests(HomeserverTestCase):
-    def prepare(self, reactor: MemoryReactor, clock: Clock, homeserver: HomeServer):
-        self.oembed = OEmbedProvider(homeserver)
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self.oembed = OEmbedProvider(hs)
 
-    def parse_response(self, response: JsonDict):
+    def parse_response(self, response: JsonDict) -> OEmbedResult:
         return self.oembed.parse_oembed_response(
             "https://test", json.dumps(response).encode("utf-8")
         )
 
-    def test_version(self):
+    def test_version(self) -> None:
         """Accept versions that are similar to 1.0 as a string or int (or missing)."""
         for version in ("1.0", 1.0, 1):
             result = self.parse_response({"version": version, "type": "link"})
diff --git a/tests/rest/media/v1/test_url_preview.py b/tests/rest/media/v1/test_url_preview.py
index da2c53326019..5148c39874e2 100644
--- a/tests/rest/media/v1/test_url_preview.py
+++ b/tests/rest/media/v1/test_url_preview.py
@@ -16,16 +16,21 @@
 import json
 import os
 import re
+from typing import Any, Dict, Optional, Sequence, Tuple, Type
 from urllib.parse import urlencode
 
 from twisted.internet._resolver import HostResolution
 from twisted.internet.address import IPv4Address, IPv6Address
 from twisted.internet.error import DNSLookupError
-from twisted.test.proto_helpers import AccumulatingProtocol
+from twisted.internet.interfaces import IAddress, IResolutionReceiver
+from twisted.test.proto_helpers import AccumulatingProtocol, MemoryReactor
 
 from synapse.config.oembed import OEmbedEndpointConfig
+from synapse.rest.media.v1.media_repository import MediaRepositoryResource
 from synapse.rest.media.v1.preview_url_resource import IMAGE_CACHE_EXPIRY_MS
+from synapse.server import HomeServer
 from synapse.types import JsonDict
+from synapse.util import Clock
 from synapse.util.stringutils import parse_and_validate_mxc_uri
 
 from tests import unittest
@@ -52,7 +57,7 @@ class URLPreviewTests(unittest.HomeserverTestCase):
         b"</head></html>"
     )
 
-    def make_homeserver(self, reactor, clock):
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
 
         config = self.default_config()
         config["url_preview_enabled"] = True
@@ -113,22 +118,22 @@ def make_homeserver(self, reactor, clock):
 
         return hs
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
 
         self.media_repo = hs.get_media_repository_resource()
         self.preview_url = self.media_repo.children[b"preview_url"]
 
-        self.lookups = {}
+        self.lookups: Dict[str, Any] = {}
 
         class Resolver:
             def resolveHostName(
                 _self,
-                resolutionReceiver,
-                hostName,
-                portNumber=0,
-                addressTypes=None,
-                transportSemantics="TCP",
-            ):
+                resolutionReceiver: IResolutionReceiver,
+                hostName: str,
+                portNumber: int = 0,
+                addressTypes: Optional[Sequence[Type[IAddress]]] = None,
+                transportSemantics: str = "TCP",
+            ) -> IResolutionReceiver:
 
                 resolution = HostResolution(hostName)
                 resolutionReceiver.resolutionBegan(resolution)
@@ -140,9 +145,9 @@ def resolveHostName(
                 resolutionReceiver.resolutionComplete()
                 return resolutionReceiver
 
-        self.reactor.nameResolver = Resolver()
+        self.reactor.nameResolver = Resolver()  # type: ignore[assignment]
 
-    def create_test_resource(self):
+    def create_test_resource(self) -> MediaRepositoryResource:
         return self.hs.get_media_repository_resource()
 
     def _assert_small_png(self, json_body: JsonDict) -> None:
@@ -153,7 +158,7 @@ def _assert_small_png(self, json_body: JsonDict) -> None:
         self.assertEqual(json_body["og:image:type"], "image/png")
         self.assertEqual(json_body["matrix:image:size"], 67)
 
-    def test_cache_returns_correct_type(self):
+    def test_cache_returns_correct_type(self) -> None:
         self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]
 
         channel = self.make_request(
@@ -207,7 +212,7 @@ def test_cache_returns_correct_type(self):
             channel.json_body, {"og:title": "~matrix~", "og:description": "hi"}
         )
 
-    def test_non_ascii_preview_httpequiv(self):
+    def test_non_ascii_preview_httpequiv(self) -> None:
         self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]
 
         end_content = (
@@ -243,7 +248,7 @@ def test_non_ascii_preview_httpequiv(self):
         self.assertEqual(channel.code, 200)
         self.assertEqual(channel.json_body["og:title"], "\u0434\u043a\u0430")
 
-    def test_video_rejected(self):
+    def test_video_rejected(self) -> None:
         self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]
 
         end_content = b"anything"
@@ -279,7 +284,7 @@ def test_video_rejected(self):
             },
         )
 
-    def test_audio_rejected(self):
+    def test_audio_rejected(self) -> None:
         self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]
 
         end_content = b"anything"
@@ -315,7 +320,7 @@ def test_audio_rejected(self):
             },
         )
 
-    def test_non_ascii_preview_content_type(self):
+    def test_non_ascii_preview_content_type(self) -> None:
         self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]
 
         end_content = (
@@ -350,7 +355,7 @@ def test_non_ascii_preview_content_type(self):
         self.assertEqual(channel.code, 200)
         self.assertEqual(channel.json_body["og:title"], "\u0434\u043a\u0430")
 
-    def test_overlong_title(self):
+    def test_overlong_title(self) -> None:
         self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]
 
         end_content = (
@@ -387,7 +392,7 @@ def test_overlong_title(self):
         # We should only see the `og:description` field, as `title` is too long and should be stripped out
         self.assertCountEqual(["og:description"], res.keys())
 
-    def test_ipaddr(self):
+    def test_ipaddr(self) -> None:
         """
         IP addresses can be previewed directly.
         """
@@ -417,7 +422,7 @@ def test_ipaddr(self):
             channel.json_body, {"og:title": "~matrix~", "og:description": "hi"}
         )
 
-    def test_blacklisted_ip_specific(self):
+    def test_blacklisted_ip_specific(self) -> None:
         """
         Blacklisted IP addresses, found via DNS, are not spidered.
         """
@@ -438,7 +443,7 @@ def test_blacklisted_ip_specific(self):
             },
         )
 
-    def test_blacklisted_ip_range(self):
+    def test_blacklisted_ip_range(self) -> None:
         """
         Blacklisted IP ranges, IPs found over DNS, are not spidered.
         """
@@ -457,7 +462,7 @@ def test_blacklisted_ip_range(self):
             },
         )
 
-    def test_blacklisted_ip_specific_direct(self):
+    def test_blacklisted_ip_specific_direct(self) -> None:
         """
         Blacklisted IP addresses, accessed directly, are not spidered.
         """
@@ -476,7 +481,7 @@ def test_blacklisted_ip_specific_direct(self):
         )
         self.assertEqual(channel.code, 403)
 
-    def test_blacklisted_ip_range_direct(self):
+    def test_blacklisted_ip_range_direct(self) -> None:
         """
         Blacklisted IP ranges, accessed directly, are not spidered.
         """
@@ -493,7 +498,7 @@ def test_blacklisted_ip_range_direct(self):
             },
         )
 
-    def test_blacklisted_ip_range_whitelisted_ip(self):
+    def test_blacklisted_ip_range_whitelisted_ip(self) -> None:
         """
         Blacklisted but then subsequently whitelisted IP addresses can be
         spidered.
@@ -526,7 +531,7 @@ def test_blacklisted_ip_range_whitelisted_ip(self):
             channel.json_body, {"og:title": "~matrix~", "og:description": "hi"}
         )
 
-    def test_blacklisted_ip_with_external_ip(self):
+    def test_blacklisted_ip_with_external_ip(self) -> None:
         """
         If a hostname resolves a blacklisted IP, even if there's a
         non-blacklisted one, it will be rejected.
@@ -549,7 +554,7 @@ def test_blacklisted_ip_with_external_ip(self):
             },
         )
 
-    def test_blacklisted_ipv6_specific(self):
+    def test_blacklisted_ipv6_specific(self) -> None:
         """
         Blacklisted IP addresses, found via DNS, are not spidered.
         """
@@ -572,7 +577,7 @@ def test_blacklisted_ipv6_specific(self):
             },
         )
 
-    def test_blacklisted_ipv6_range(self):
+    def test_blacklisted_ipv6_range(self) -> None:
         """
         Blacklisted IP ranges, IPs found over DNS, are not spidered.
         """
@@ -591,7 +596,7 @@ def test_blacklisted_ipv6_range(self):
             },
         )
 
-    def test_OPTIONS(self):
+    def test_OPTIONS(self) -> None:
         """
         OPTIONS returns the OPTIONS.
         """
@@ -601,7 +606,7 @@ def test_OPTIONS(self):
         self.assertEqual(channel.code, 200)
         self.assertEqual(channel.json_body, {})
 
-    def test_accept_language_config_option(self):
+    def test_accept_language_config_option(self) -> None:
         """
         Accept-Language header is sent to the remote server
         """
@@ -652,7 +657,7 @@ def test_accept_language_config_option(self):
             server.data,
         )
 
-    def test_data_url(self):
+    def test_data_url(self) -> None:
         """
         Requesting to preview a data URL is not supported.
         """
@@ -675,7 +680,7 @@ def test_data_url(self):
 
         self.assertEqual(channel.code, 500)
 
-    def test_inline_data_url(self):
+    def test_inline_data_url(self) -> None:
         """
         An inline image (as a data URL) should be parsed properly.
         """
@@ -712,7 +717,7 @@ def test_inline_data_url(self):
         self.assertEqual(channel.code, 200)
         self._assert_small_png(channel.json_body)
 
-    def test_oembed_photo(self):
+    def test_oembed_photo(self) -> None:
         """Test an oEmbed endpoint which returns a 'photo' type which redirects the preview to a new URL."""
         self.lookups["publish.twitter.com"] = [(IPv4Address, "10.1.2.3")]
         self.lookups["cdn.twitter.com"] = [(IPv4Address, "10.1.2.3")]
@@ -771,7 +776,7 @@ def test_oembed_photo(self):
         self.assertEqual(body["og:url"], "http://twitter.com/matrixdotorg/status/12345")
         self._assert_small_png(body)
 
-    def test_oembed_rich(self):
+    def test_oembed_rich(self) -> None:
         """Test an oEmbed endpoint which returns HTML content via the 'rich' type."""
         self.lookups["publish.twitter.com"] = [(IPv4Address, "10.1.2.3")]
 
@@ -817,7 +822,7 @@ def test_oembed_rich(self):
             },
         )
 
-    def test_oembed_format(self):
+    def test_oembed_format(self) -> None:
         """Test an oEmbed endpoint which requires the format in the URL."""
         self.lookups["www.hulu.com"] = [(IPv4Address, "10.1.2.3")]
 
@@ -866,7 +871,7 @@ def test_oembed_format(self):
             },
         )
 
-    def test_oembed_autodiscovery(self):
+    def test_oembed_autodiscovery(self) -> None:
         """
         Autodiscovery works by finding the link in the HTML response and then requesting an oEmbed URL.
         1. Request a preview of a URL which is not known to the oEmbed code.
@@ -962,7 +967,7 @@ def test_oembed_autodiscovery(self):
         )
         self._assert_small_png(body)
 
-    def _download_image(self):
+    def _download_image(self) -> Tuple[str, str]:
         """Downloads an image into the URL cache.
         Returns:
             A (host, media_id) tuple representing the MXC URI of the image.
@@ -995,7 +1000,7 @@ def _download_image(self):
         self.assertIsNone(_port)
         return host, media_id
 
-    def test_storage_providers_exclude_files(self):
+    def test_storage_providers_exclude_files(self) -> None:
         """Test that files are not stored in or fetched from storage providers."""
         host, media_id = self._download_image()
 
@@ -1037,7 +1042,7 @@ def test_storage_providers_exclude_files(self):
             "URL cache file was unexpectedly retrieved from a storage provider",
         )
 
-    def test_storage_providers_exclude_thumbnails(self):
+    def test_storage_providers_exclude_thumbnails(self) -> None:
         """Test that thumbnails are not stored in or fetched from storage providers."""
         host, media_id = self._download_image()
 
@@ -1090,7 +1095,7 @@ def test_storage_providers_exclude_thumbnails(self):
             "URL cache thumbnail was unexpectedly retrieved from a storage provider",
         )
 
-    def test_cache_expiry(self):
+    def test_cache_expiry(self) -> None:
         """Test that URL cache files and thumbnails are cleaned up properly on expiry."""
         self.preview_url.clock = MockClock()
 
diff --git a/tests/rest/test_health.py b/tests/rest/test_health.py
index 01d48c3860d4..da325955f86f 100644
--- a/tests/rest/test_health.py
+++ b/tests/rest/test_health.py
@@ -11,7 +11,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-
+from http import HTTPStatus
 
 from synapse.rest.health import HealthResource
 
@@ -19,12 +19,12 @@
 
 
 class HealthCheckTests(unittest.HomeserverTestCase):
-    def create_test_resource(self):
+    def create_test_resource(self) -> HealthResource:
         # replace the JsonResource with a HealthResource.
         return HealthResource()
 
-    def test_health(self):
+    def test_health(self) -> None:
         channel = self.make_request("GET", "/health", shorthand=False)
 
-        self.assertEqual(channel.code, 200)
+        self.assertEqual(channel.code, HTTPStatus.OK)
         self.assertEqual(channel.result["body"], b"OK")
diff --git a/tests/rest/test_well_known.py b/tests/rest/test_well_known.py
index 118aa93a320d..11f78f52b87a 100644
--- a/tests/rest/test_well_known.py
+++ b/tests/rest/test_well_known.py
@@ -11,6 +11,8 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+from http import HTTPStatus
+
 from twisted.web.resource import Resource
 
 from synapse.rest.well_known import well_known_resource
@@ -19,7 +21,7 @@
 
 
 class WellKnownTests(unittest.HomeserverTestCase):
-    def create_test_resource(self):
+    def create_test_resource(self) -> Resource:
         # replace the JsonResource with a Resource wrapping the WellKnownResource
         res = Resource()
         res.putChild(b".well-known", well_known_resource(self.hs))
@@ -31,12 +33,12 @@ def create_test_resource(self):
             "default_identity_server": "https://testis",
         }
     )
-    def test_client_well_known(self):
+    def test_client_well_known(self) -> None:
         channel = self.make_request(
             "GET", "/.well-known/matrix/client", shorthand=False
         )
 
-        self.assertEqual(channel.code, 200)
+        self.assertEqual(channel.code, HTTPStatus.OK)
         self.assertEqual(
             channel.json_body,
             {
@@ -50,27 +52,27 @@ def test_client_well_known(self):
             "public_baseurl": None,
         }
     )
-    def test_client_well_known_no_public_baseurl(self):
+    def test_client_well_known_no_public_baseurl(self) -> None:
         channel = self.make_request(
             "GET", "/.well-known/matrix/client", shorthand=False
         )
 
-        self.assertEqual(channel.code, 404)
+        self.assertEqual(channel.code, HTTPStatus.NOT_FOUND)
 
     @unittest.override_config({"serve_server_wellknown": True})
-    def test_server_well_known(self):
+    def test_server_well_known(self) -> None:
         channel = self.make_request(
             "GET", "/.well-known/matrix/server", shorthand=False
         )
 
-        self.assertEqual(channel.code, 200)
+        self.assertEqual(channel.code, HTTPStatus.OK)
         self.assertEqual(
             channel.json_body,
             {"m.server": "test:443"},
         )
 
-    def test_server_well_known_disabled(self):
+    def test_server_well_known_disabled(self) -> None:
         channel = self.make_request(
             "GET", "/.well-known/matrix/server", shorthand=False
         )
-        self.assertEqual(channel.code, 404)
+        self.assertEqual(channel.code, HTTPStatus.NOT_FOUND)
diff --git a/tests/storage/test_background_update.py b/tests/storage/test_background_update.py
index 39dcc094bd8b..5cf18b690e48 100644
--- a/tests/storage/test_background_update.py
+++ b/tests/storage/test_background_update.py
@@ -14,12 +14,15 @@
 
 from unittest.mock import Mock
 
+import yaml
+
 from twisted.internet.defer import Deferred, ensureDeferred
 
 from synapse.storage.background_updates import BackgroundUpdater
 
 from tests import unittest
 from tests.test_utils import make_awaitable, simple_async_mock
+from tests.unittest import override_config
 
 
 class BackgroundUpdateTestCase(unittest.HomeserverTestCase):
@@ -34,6 +37,19 @@ def prepare(self, reactor, clock, homeserver):
         self.updates.register_background_update_handler(
             "test_update", self.update_handler
         )
+        self.store = self.hs.get_datastores().main
+
+    async def update(self, progress, count):
+        duration_ms = 10
+        await self.clock.sleep((count * duration_ms) / 1000)
+        progress = {"my_key": progress["my_key"] + 1}
+        await self.store.db_pool.runInteraction(
+            "update_progress",
+            self.updates._background_update_progress_txn,
+            "test_update",
+            progress,
+        )
+        return count
 
     def test_do_background_update(self):
         # the time we claim it takes to update one item when running the update
@@ -42,37 +58,24 @@ def test_do_background_update(self):
         # the target runtime for each bg update
         target_background_update_duration_ms = 100
 
-        store = self.hs.get_datastores().main
         self.get_success(
-            store.db_pool.simple_insert(
+            self.store.db_pool.simple_insert(
                 "background_updates",
                 values={"update_name": "test_update", "progress_json": '{"my_key": 1}'},
             )
         )
 
-        # first step: make a bit of progress
-        async def update(progress, count):
-            await self.clock.sleep((count * duration_ms) / 1000)
-            progress = {"my_key": progress["my_key"] + 1}
-            await store.db_pool.runInteraction(
-                "update_progress",
-                self.updates._background_update_progress_txn,
-                "test_update",
-                progress,
-            )
-            return count
-
-        self.update_handler.side_effect = update
+        self.update_handler.side_effect = self.update
         self.update_handler.reset_mock()
         res = self.get_success(
             self.updates.do_next_background_update(False),
-            by=0.01,
+            by=0.02,
         )
         self.assertFalse(res)
 
         # on the first call, we should get run with the default background update size
         self.update_handler.assert_called_once_with(
-            {"my_key": 1}, self.updates.MINIMUM_BACKGROUND_BATCH_SIZE
+            {"my_key": 1}, self.updates.default_background_batch_size
         )
 
         # second step: complete the update
@@ -99,6 +102,224 @@ async def update(progress, count):
         self.assertTrue(result)
         self.assertFalse(self.update_handler.called)
 
+    @override_config(
+        yaml.safe_load(
+            """
+            background_updates:
+                default_batch_size: 20
+            """
+        )
+    )
+    def test_background_update_default_batch_set_by_config(self):
+        """
+        Test that the background update is run with the default_batch_size set by the config
+        """
+
+        self.get_success(
+            self.store.db_pool.simple_insert(
+                "background_updates",
+                values={"update_name": "test_update", "progress_json": '{"my_key": 1}'},
+            )
+        )
+
+        self.update_handler.side_effect = self.update
+        self.update_handler.reset_mock()
+        res = self.get_success(
+            self.updates.do_next_background_update(False),
+            by=0.01,
+        )
+        self.assertFalse(res)
+
+        # on the first call, we should get run with the default background update size specified in the config
+        self.update_handler.assert_called_once_with({"my_key": 1}, 20)
+
+    def test_background_update_default_sleep_behavior(self):
+        """
+        Test default background update behavior, which is to sleep
+        """
+
+        self.get_success(
+            self.store.db_pool.simple_insert(
+                "background_updates",
+                values={"update_name": "test_update", "progress_json": '{"my_key": 1}'},
+            )
+        )
+
+        self.update_handler.side_effect = self.update
+        self.update_handler.reset_mock()
+        self.updates.start_doing_background_updates(),
+
+        # 2: advance the reactor less than the default sleep duration (1000ms)
+        self.reactor.pump([0.5])
+        # check that an update has not been run
+        self.update_handler.assert_not_called()
+
+        # advance reactor past default sleep duration
+        self.reactor.pump([1])
+        # check that update has been run
+        self.update_handler.assert_called()
+
+    @override_config(
+        yaml.safe_load(
+            """
+            background_updates:
+                sleep_duration_ms: 500
+            """
+        )
+    )
+    def test_background_update_sleep_set_in_config(self):
+        """
+        Test that changing the sleep time in the config changes how long it sleeps
+        """
+
+        self.get_success(
+            self.store.db_pool.simple_insert(
+                "background_updates",
+                values={"update_name": "test_update", "progress_json": '{"my_key": 1}'},
+            )
+        )
+
+        self.update_handler.side_effect = self.update
+        self.update_handler.reset_mock()
+        self.updates.start_doing_background_updates(),
+
+        # 2: advance the reactor less than the configured sleep duration (500ms)
+        self.reactor.pump([0.45])
+        # check that an update has not been run
+        self.update_handler.assert_not_called()
+
+        # advance reactor past config sleep duration but less than default duration
+        self.reactor.pump([0.75])
+        # check that update has been run
+        self.update_handler.assert_called()
+
+    @override_config(
+        yaml.safe_load(
+            """
+            background_updates:
+                sleep_enabled: false
+            """
+        )
+    )
+    def test_disabling_background_update_sleep(self):
+        """
+        Test that disabling sleep in the config results in bg update not sleeping
+        """
+
+        self.get_success(
+            self.store.db_pool.simple_insert(
+                "background_updates",
+                values={"update_name": "test_update", "progress_json": '{"my_key": 1}'},
+            )
+        )
+
+        self.update_handler.side_effect = self.update
+        self.update_handler.reset_mock()
+        self.updates.start_doing_background_updates(),
+
+        # 2: advance the reactor very little
+        self.reactor.pump([0.025])
+        # check that an update has run
+        self.update_handler.assert_called()
+
+    @override_config(
+        yaml.safe_load(
+            """
+            background_updates:
+                background_update_duration_ms: 500
+            """
+        )
+    )
+    def test_background_update_duration_set_in_config(self):
+        """
+        Test that the desired duration set in the config is used in determining batch size
+        """
+        # Duration of one background update item
+        duration_ms = 10
+
+        self.get_success(
+            self.store.db_pool.simple_insert(
+                "background_updates",
+                values={"update_name": "test_update", "progress_json": '{"my_key": 1}'},
+            )
+        )
+
+        self.update_handler.side_effect = self.update
+        self.update_handler.reset_mock()
+        res = self.get_success(
+            self.updates.do_next_background_update(False),
+            by=0.02,
+        )
+        self.assertFalse(res)
+
+        # the first update was run with the default batch size, this should be run with 500ms as the
+        # desired duration
+        async def update(progress, count):
+            self.assertEqual(progress, {"my_key": 2})
+            self.assertAlmostEqual(
+                count,
+                500 / duration_ms,
+                places=0,
+            )
+            await self.updates._end_background_update("test_update")
+            return count
+
+        self.update_handler.side_effect = update
+        self.get_success(self.updates.do_next_background_update(False))
+
+    @override_config(
+        yaml.safe_load(
+            """
+            background_updates:
+                min_batch_size: 5
+            """
+        )
+    )
+    def test_background_update_min_batch_set_in_config(self):
+        """
+        Test that the minimum batch size set in the config is used
+        """
+        # a very long-running individual update
+        duration_ms = 50
+
+        self.get_success(
+            self.store.db_pool.simple_insert(
+                "background_updates",
+                values={"update_name": "test_update", "progress_json": '{"my_key": 1}'},
+            )
+        )
+
+        # Run the update with the long-running update item
+        async def update(progress, count):
+            await self.clock.sleep((count * duration_ms) / 1000)
+            progress = {"my_key": progress["my_key"] + 1}
+            await self.store.db_pool.runInteraction(
+                "update_progress",
+                self.updates._background_update_progress_txn,
+                "test_update",
+                progress,
+            )
+            return count
+
+        self.update_handler.side_effect = update
+        self.update_handler.reset_mock()
+        res = self.get_success(
+            self.updates.do_next_background_update(False),
+            by=1,
+        )
+        self.assertFalse(res)
+
+        # the first update was run with the default batch size, this should be run with minimum batch size
+        # as the first items took a very long time
+        async def update(progress, count):
+            self.assertEqual(progress, {"my_key": 2})
+            self.assertEqual(count, 5)
+            await self.updates._end_background_update("test_update")
+            return count
+
+        self.update_handler.side_effect = update
+        self.get_success(self.updates.do_next_background_update(False))
+
 
 class BackgroundUpdateControllerTestCase(unittest.HomeserverTestCase):
     def prepare(self, reactor, clock, homeserver):
diff --git a/tests/storage/test_database.py b/tests/storage/test_database.py
index 6fbac0ab1466..85978675634b 100644
--- a/tests/storage/test_database.py
+++ b/tests/storage/test_database.py
@@ -13,26 +13,10 @@
 # limitations under the License.
 
 from synapse.storage.database import make_tuple_comparison_clause
-from synapse.storage.engines import BaseDatabaseEngine
 
 from tests import unittest
 
 
-def _stub_db_engine(**kwargs) -> BaseDatabaseEngine:
-    # returns a DatabaseEngine, circumventing the abc mechanism
-    # any kwargs are set as attributes on the class before instantiating it
-    t = type(
-        "TestBaseDatabaseEngine",
-        (BaseDatabaseEngine,),
-        dict(BaseDatabaseEngine.__dict__),
-    )
-    # defeat the abc mechanism
-    t.__abstractmethods__ = set()
-    for k, v in kwargs.items():
-        setattr(t, k, v)
-    return t(None, None)
-
-
 class TupleComparisonClauseTestCase(unittest.TestCase):
     def test_native_tuple_comparison(self):
         clause, args = make_tuple_comparison_clause([("a", 1), ("b", 2)])
diff --git a/tests/storage/test_stream.py b/tests/storage/test_stream.py
index 6a1cf3305455..eaa0d7d749b7 100644
--- a/tests/storage/test_stream.py
+++ b/tests/storage/test_stream.py
@@ -129,21 +129,19 @@ def _filter_messages(self, filter: JsonDict) -> List[EventBase]:
 
     def test_filter_relation_senders(self):
         # Messages which second user reacted to.
-        filter = {"io.element.relation_senders": [self.second_user_id]}
+        filter = {"related_by_senders": [self.second_user_id]}
         chunk = self._filter_messages(filter)
         self.assertEqual(len(chunk), 1, chunk)
         self.assertEqual(chunk[0].event_id, self.event_id_1)
 
         # Messages which third user reacted to.
-        filter = {"io.element.relation_senders": [self.third_user_id]}
+        filter = {"related_by_senders": [self.third_user_id]}
         chunk = self._filter_messages(filter)
         self.assertEqual(len(chunk), 1, chunk)
         self.assertEqual(chunk[0].event_id, self.event_id_2)
 
         # Messages which either user reacted to.
-        filter = {
-            "io.element.relation_senders": [self.second_user_id, self.third_user_id]
-        }
+        filter = {"related_by_senders": [self.second_user_id, self.third_user_id]}
         chunk = self._filter_messages(filter)
         self.assertEqual(len(chunk), 2, chunk)
         self.assertCountEqual(
@@ -152,20 +150,20 @@ def test_filter_relation_senders(self):
 
     def test_filter_relation_type(self):
         # Messages which have annotations.
-        filter = {"io.element.relation_types": [RelationTypes.ANNOTATION]}
+        filter = {"related_by_rel_types": [RelationTypes.ANNOTATION]}
         chunk = self._filter_messages(filter)
         self.assertEqual(len(chunk), 1, chunk)
         self.assertEqual(chunk[0].event_id, self.event_id_1)
 
         # Messages which have references.
-        filter = {"io.element.relation_types": [RelationTypes.REFERENCE]}
+        filter = {"related_by_rel_types": [RelationTypes.REFERENCE]}
         chunk = self._filter_messages(filter)
         self.assertEqual(len(chunk), 1, chunk)
         self.assertEqual(chunk[0].event_id, self.event_id_2)
 
         # Messages which have either annotations or references.
         filter = {
-            "io.element.relation_types": [
+            "related_by_rel_types": [
                 RelationTypes.ANNOTATION,
                 RelationTypes.REFERENCE,
             ]
@@ -179,8 +177,8 @@ def test_filter_relation_type(self):
     def test_filter_relation_senders_and_type(self):
         # Messages which second user reacted to.
         filter = {
-            "io.element.relation_senders": [self.second_user_id],
-            "io.element.relation_types": [RelationTypes.ANNOTATION],
+            "related_by_senders": [self.second_user_id],
+            "related_by_rel_types": [RelationTypes.ANNOTATION],
         }
         chunk = self._filter_messages(filter)
         self.assertEqual(len(chunk), 1, chunk)
@@ -201,7 +199,7 @@ def test_duplicate_relation(self):
             tok=self.second_tok,
         )
 
-        filter = {"io.element.relation_senders": [self.second_user_id]}
+        filter = {"related_by_senders": [self.second_user_id]}
         chunk = self._filter_messages(filter)
         self.assertEqual(len(chunk), 1, chunk)
         self.assertEqual(chunk[0].event_id, self.event_id_1)
diff --git a/tests/test_visibility.py b/tests/test_visibility.py
index 219b5660b117..532e3fe9cd92 100644
--- a/tests/test_visibility.py
+++ b/tests/test_visibility.py
@@ -13,11 +13,12 @@
 # limitations under the License.
 import logging
 from typing import Optional
+from unittest.mock import patch
 
 from synapse.api.room_versions import RoomVersions
-from synapse.events import EventBase
-from synapse.types import JsonDict
-from synapse.visibility import filter_events_for_server
+from synapse.events import EventBase, make_event_from_dict
+from synapse.types import JsonDict, create_requester
+from synapse.visibility import filter_events_for_client, filter_events_for_server
 
 from tests import unittest
 from tests.utils import create_room
@@ -185,3 +186,72 @@ def _inject_message(
 
         self.get_success(self.storage.persistence.persist_event(event, context))
         return event
+
+
+class FilterEventsForClientTestCase(unittest.FederatingHomeserverTestCase):
+    def test_out_of_band_invite_rejection(self):
+        # this is where we have received an invite event over federation, and then
+        # rejected it.
+        invite_pdu = {
+            "room_id": "!room:id",
+            "depth": 1,
+            "auth_events": [],
+            "prev_events": [],
+            "origin_server_ts": 1,
+            "sender": "@someone:" + self.OTHER_SERVER_NAME,
+            "type": "m.room.member",
+            "state_key": "@user:test",
+            "content": {"membership": "invite"},
+        }
+        self.add_hashes_and_signatures(invite_pdu)
+        invite_event_id = make_event_from_dict(invite_pdu, RoomVersions.V9).event_id
+
+        self.get_success(
+            self.hs.get_federation_server().on_invite_request(
+                self.OTHER_SERVER_NAME,
+                invite_pdu,
+                "9",
+            )
+        )
+
+        # stub out do_remotely_reject_invite so that we fall back to a locally-
+        # generated rejection
+        with patch.object(
+            self.hs.get_federation_handler(),
+            "do_remotely_reject_invite",
+            side_effect=Exception(),
+        ):
+            reject_event_id, _ = self.get_success(
+                self.hs.get_room_member_handler().remote_reject_invite(
+                    invite_event_id,
+                    txn_id=None,
+                    requester=create_requester("@user:test"),
+                    content={},
+                )
+            )
+
+        invite_event, reject_event = self.get_success(
+            self.hs.get_datastores().main.get_events_as_list(
+                [invite_event_id, reject_event_id]
+            )
+        )
+
+        # the invited user should be able to see both the invite and the rejection
+        self.assertEqual(
+            self.get_success(
+                filter_events_for_client(
+                    self.hs.get_storage(), "@user:test", [invite_event, reject_event]
+                )
+            ),
+            [invite_event, reject_event],
+        )
+
+        # other users should see neither
+        self.assertEqual(
+            self.get_success(
+                filter_events_for_client(
+                    self.hs.get_storage(), "@other:test", [invite_event, reject_event]
+                )
+            ),
+            [],
+        )
diff --git a/tests/util/caches/test_descriptors.py b/tests/util/caches/test_descriptors.py
index 19741ffcdaf1..48e616ac7419 100644
--- a/tests/util/caches/test_descriptors.py
+++ b/tests/util/caches/test_descriptors.py
@@ -17,7 +17,7 @@
 from unittest import mock
 
 from twisted.internet import defer, reactor
-from twisted.internet.defer import Deferred
+from twisted.internet.defer import CancelledError, Deferred
 
 from synapse.api.errors import SynapseError
 from synapse.logging.context import (
@@ -28,7 +28,7 @@
     make_deferred_yieldable,
 )
 from synapse.util.caches import descriptors
-from synapse.util.caches.descriptors import cached, lru_cache
+from synapse.util.caches.descriptors import cached, cachedList, lru_cache
 
 from tests import unittest
 from tests.test_utils import get_awaitable_result
@@ -141,6 +141,84 @@ def fn(self, arg1, arg2):
         self.assertEqual(r, "chips")
         obj.mock.assert_not_called()
 
+    @defer.inlineCallbacks
+    def test_cache_uncached_args(self):
+        """
+        Only the arguments not named in uncached_args should matter to the cache
+
+        Note that this is identical to test_cache_num_args, but provides the
+        arguments differently.
+        """
+
+        class Cls:
+            # Note that it is important that this is not the last argument to
+            # test behaviour of skipping arguments properly.
+            @descriptors.cached(uncached_args=("arg2",))
+            def fn(self, arg1, arg2, arg3):
+                return self.mock(arg1, arg2, arg3)
+
+            def __init__(self):
+                self.mock = mock.Mock()
+
+        obj = Cls()
+        obj.mock.return_value = "fish"
+        r = yield obj.fn(1, 2, 3)
+        self.assertEqual(r, "fish")
+        obj.mock.assert_called_once_with(1, 2, 3)
+        obj.mock.reset_mock()
+
+        # a call with different params should call the mock again
+        obj.mock.return_value = "chips"
+        r = yield obj.fn(2, 3, 4)
+        self.assertEqual(r, "chips")
+        obj.mock.assert_called_once_with(2, 3, 4)
+        obj.mock.reset_mock()
+
+        # the two values should now be cached; we should be able to vary
+        # the second argument and still get the cached result.
+        r = yield obj.fn(1, 4, 3)
+        self.assertEqual(r, "fish")
+        r = yield obj.fn(2, 5, 4)
+        self.assertEqual(r, "chips")
+        obj.mock.assert_not_called()
+
+    @defer.inlineCallbacks
+    def test_cache_kwargs(self):
+        """Test that keyword arguments are treated properly"""
+
+        class Cls:
+            def __init__(self):
+                self.mock = mock.Mock()
+
+            @descriptors.cached()
+            def fn(self, arg1, kwarg1=2):
+                return self.mock(arg1, kwarg1=kwarg1)
+
+        obj = Cls()
+        obj.mock.return_value = "fish"
+        r = yield obj.fn(1, kwarg1=2)
+        self.assertEqual(r, "fish")
+        obj.mock.assert_called_once_with(1, kwarg1=2)
+        obj.mock.reset_mock()
+
+        # a call with different params should call the mock again
+        obj.mock.return_value = "chips"
+        r = yield obj.fn(1, kwarg1=3)
+        self.assertEqual(r, "chips")
+        obj.mock.assert_called_once_with(1, kwarg1=3)
+        obj.mock.reset_mock()
+
+        # the values should now be cached.
+        r = yield obj.fn(1, kwarg1=2)
+        self.assertEqual(r, "fish")
+        # We should be able to not provide kwarg1 and get the cached value back.
+        r = yield obj.fn(1)
+        self.assertEqual(r, "fish")
+        # Keyword arguments can be in any order.
+        r = yield obj.fn(kwarg1=2, arg1=1)
+        self.assertEqual(r, "fish")
+        obj.mock.assert_not_called()
+
     def test_cache_with_sync_exception(self):
         """If the wrapped function throws synchronously, things should continue to work"""
 
@@ -415,6 +493,74 @@ def func3(self, key, cache_context):
         obj.invalidate()
         top_invalidate.assert_called_once()
 
+    def test_cancel(self):
+        """Test that cancelling a lookup does not cancel other lookups"""
+        complete_lookup: "Deferred[None]" = Deferred()
+
+        class Cls:
+            @cached()
+            async def fn(self, arg1):
+                await complete_lookup
+                return str(arg1)
+
+        obj = Cls()
+
+        d1 = obj.fn(123)
+        d2 = obj.fn(123)
+        self.assertFalse(d1.called)
+        self.assertFalse(d2.called)
+
+        # Cancel `d1`, which is the lookup that caused `fn` to run.
+        d1.cancel()
+
+        # `d2` should complete normally.
+        complete_lookup.callback(None)
+        self.failureResultOf(d1, CancelledError)
+        self.assertEqual(d2.result, "123")
+
+    def test_cancel_logcontexts(self):
+        """Test that cancellation does not break logcontexts.
+
+        * The `CancelledError` must be raised with the correct logcontext.
+        * The inner lookup must not resume with a finished logcontext.
+        * The inner lookup must not restore a finished logcontext when done.
+        """
+        complete_lookup: "Deferred[None]" = Deferred()
+
+        class Cls:
+            inner_context_was_finished = False
+
+            @cached()
+            async def fn(self, arg1):
+                await make_deferred_yieldable(complete_lookup)
+                self.inner_context_was_finished = current_context().finished
+                return str(arg1)
+
+        obj = Cls()
+
+        async def do_lookup():
+            with LoggingContext("c1") as c1:
+                try:
+                    await obj.fn(123)
+                    self.fail("No CancelledError thrown")
+                except CancelledError:
+                    self.assertEqual(
+                        current_context(),
+                        c1,
+                        "CancelledError was not raised with the correct logcontext",
+                    )
+                    # suppress the error and succeed
+
+        d = defer.ensureDeferred(do_lookup())
+        d.cancel()
+
+        complete_lookup.callback(None)
+        self.successResultOf(d)
+        self.assertFalse(
+            obj.inner_context_was_finished, "Tried to restart a finished logcontext"
+        )
+        self.assertEqual(current_context(), SENTINEL_CONTEXT)
+
 
 class CacheDecoratorTestCase(unittest.HomeserverTestCase):
     """More tests for @cached
@@ -656,7 +802,7 @@ def __init__(self):
             def fn(self, arg1, arg2):
                 pass
 
-            @descriptors.cachedList("fn", "args1")
+            @descriptors.cachedList(cached_method_name="fn", list_name="args1")
             async def list_fn(self, args1, arg2):
                 assert current_context().name == "c1"
                 # we want this to behave like an asynchronous function
@@ -715,7 +861,7 @@ def __init__(self):
             def fn(self, arg1):
                 pass
 
-            @descriptors.cachedList("fn", "args1")
+            @descriptors.cachedList(cached_method_name="fn", list_name="args1")
             def list_fn(self, args1) -> "Deferred[dict]":
                 return self.mock(args1)
 
@@ -758,7 +904,7 @@ def __init__(self):
             def fn(self, arg1, arg2):
                 pass
 
-            @descriptors.cachedList("fn", "args1")
+            @descriptors.cachedList(cached_method_name="fn", list_name="args1")
             async def list_fn(self, args1, arg2):
                 # we want this to behave like an asynchronous function
                 await run_on_reactor()
@@ -787,3 +933,78 @@ async def list_fn(self, args1, arg2):
         obj.fn.invalidate((10, 2))
         invalidate0.assert_called_once()
         invalidate1.assert_called_once()
+
+    def test_cancel(self):
+        """Test that cancelling a lookup does not cancel other lookups"""
+        complete_lookup: "Deferred[None]" = Deferred()
+
+        class Cls:
+            @cached()
+            def fn(self, arg1):
+                pass
+
+            @cachedList(cached_method_name="fn", list_name="args")
+            async def list_fn(self, args):
+                await complete_lookup
+                return {arg: str(arg) for arg in args}
+
+        obj = Cls()
+
+        d1 = obj.list_fn([123, 456])
+        d2 = obj.list_fn([123, 456, 789])
+        self.assertFalse(d1.called)
+        self.assertFalse(d2.called)
+
+        d1.cancel()
+
+        # `d2` should complete normally.
+        complete_lookup.callback(None)
+        self.failureResultOf(d1, CancelledError)
+        self.assertEqual(d2.result, {123: "123", 456: "456", 789: "789"})
+
+    def test_cancel_logcontexts(self):
+        """Test that cancellation does not break logcontexts.
+
+        * The `CancelledError` must be raised with the correct logcontext.
+        * The inner lookup must not resume with a finished logcontext.
+        * The inner lookup must not restore a finished logcontext when done.
+        """
+        complete_lookup: "Deferred[None]" = Deferred()
+
+        class Cls:
+            inner_context_was_finished = False
+
+            @cached()
+            def fn(self, arg1):
+                pass
+
+            @cachedList(cached_method_name="fn", list_name="args")
+            async def list_fn(self, args):
+                await make_deferred_yieldable(complete_lookup)
+                self.inner_context_was_finished = current_context().finished
+                return {arg: str(arg) for arg in args}
+
+        obj = Cls()
+
+        async def do_lookup():
+            with LoggingContext("c1") as c1:
+                try:
+                    await obj.list_fn([123])
+                    self.fail("No CancelledError thrown")
+                except CancelledError:
+                    self.assertEqual(
+                        current_context(),
+                        c1,
+                        "CancelledError was not raised with the correct logcontext",
+                    )
+                    # suppress the error and succeed
+
+        d = defer.ensureDeferred(do_lookup())
+        d.cancel()
+
+        complete_lookup.callback(None)
+        self.successResultOf(d)
+        self.assertFalse(
+            obj.inner_context_was_finished, "Tried to restart a finished logcontext"
+        )
+        self.assertEqual(current_context(), SENTINEL_CONTEXT)
diff --git a/tests/util/test_async_helpers.py b/tests/util/test_async_helpers.py
index 362014f4cb6f..e5bc416de12f 100644
--- a/tests/util/test_async_helpers.py
+++ b/tests/util/test_async_helpers.py
@@ -13,6 +13,8 @@
 # limitations under the License.
 import traceback
 
+from parameterized import parameterized_class
+
 from twisted.internet import defer
 from twisted.internet.defer import CancelledError, Deferred, ensureDeferred
 from twisted.internet.task import Clock
@@ -23,10 +25,12 @@
     LoggingContext,
     PreserveLoggingContext,
     current_context,
+    make_deferred_yieldable,
 )
 from synapse.util.async_helpers import (
     ObservableDeferred,
     concurrently_execute,
+    delay_cancellation,
     stop_cancellation,
     timeout_deferred,
 )
@@ -100,6 +104,34 @@ def check_val(res, idx):
         self.assertEqual(str(results[0].value), "gah!", "observer 1 errback result")
         self.assertEqual(str(results[1].value), "gah!", "observer 2 errback result")
 
+    def test_cancellation(self):
+        """Test that cancelling an observer does not affect other observers."""
+        origin_d: "Deferred[int]" = Deferred()
+        observable = ObservableDeferred(origin_d, consumeErrors=True)
+
+        observer1 = observable.observe()
+        observer2 = observable.observe()
+        observer3 = observable.observe()
+
+        self.assertFalse(observer1.called)
+        self.assertFalse(observer2.called)
+        self.assertFalse(observer3.called)
+
+        # cancel the second observer
+        observer2.cancel()
+        self.assertFalse(observer1.called)
+        self.failureResultOf(observer2, CancelledError)
+        self.assertFalse(observer3.called)
+
+        # other observers resolve as normal
+        origin_d.callback(123)
+        self.assertEqual(observer1.result, 123, "observer 1 callback result")
+        self.assertEqual(observer3.result, 123, "observer 3 callback result")
+
+        # additional observers resolve as normal
+        observer4 = observable.observe()
+        self.assertEqual(observer4.result, 123, "observer 4 callback result")
+
 
 class TimeoutDeferredTest(TestCase):
     def setUp(self):
@@ -285,13 +317,27 @@ async def caller():
         self.successResultOf(d2)
 
 
-class StopCancellationTests(TestCase):
-    """Tests for the `stop_cancellation` function."""
+@parameterized_class(
+    ("wrapper",),
+    [("stop_cancellation",), ("delay_cancellation",)],
+)
+class CancellationWrapperTests(TestCase):
+    """Common tests for the `stop_cancellation` and `delay_cancellation` functions."""
+
+    wrapper: str
+
+    def wrap_deferred(self, deferred: "Deferred[str]") -> "Deferred[str]":
+        if self.wrapper == "stop_cancellation":
+            return stop_cancellation(deferred)
+        elif self.wrapper == "delay_cancellation":
+            return delay_cancellation(deferred)
+        else:
+            raise ValueError(f"Unsupported wrapper type: {self.wrapper}")
 
     def test_succeed(self):
         """Test that the new `Deferred` receives the result."""
         deferred: "Deferred[str]" = Deferred()
-        wrapper_deferred = stop_cancellation(deferred)
+        wrapper_deferred = self.wrap_deferred(deferred)
 
         # Success should propagate through.
         deferred.callback("success")
@@ -301,7 +347,7 @@ def test_succeed(self):
     def test_failure(self):
         """Test that the new `Deferred` receives the `Failure`."""
         deferred: "Deferred[str]" = Deferred()
-        wrapper_deferred = stop_cancellation(deferred)
+        wrapper_deferred = self.wrap_deferred(deferred)
 
         # Failure should propagate through.
         deferred.errback(ValueError("abc"))
@@ -309,6 +355,10 @@ def test_failure(self):
         self.failureResultOf(wrapper_deferred, ValueError)
         self.assertIsNone(deferred.result, "`Failure` was not consumed")
 
+
+class StopCancellationTests(TestCase):
+    """Tests for the `stop_cancellation` function."""
+
     def test_cancellation(self):
         """Test that cancellation of the new `Deferred` leaves the original running."""
         deferred: "Deferred[str]" = Deferred()
@@ -319,11 +369,101 @@ def test_cancellation(self):
         self.assertTrue(wrapper_deferred.called)
         self.failureResultOf(wrapper_deferred, CancelledError)
         self.assertFalse(
-            deferred.called, "Original `Deferred` was unexpectedly cancelled."
+            deferred.called, "Original `Deferred` was unexpectedly cancelled"
+        )
+
+        # Now make the original `Deferred` fail.
+        # The `Failure` must be consumed, otherwise unwanted tracebacks will be printed
+        # in logs.
+        deferred.errback(ValueError("abc"))
+        self.assertIsNone(deferred.result, "`Failure` was not consumed")
+
+
+class DelayCancellationTests(TestCase):
+    """Tests for the `delay_cancellation` function."""
+
+    def test_cancellation(self):
+        """Test that cancellation of the new `Deferred` waits for the original."""
+        deferred: "Deferred[str]" = Deferred()
+        wrapper_deferred = delay_cancellation(deferred)
+
+        # Cancel the new `Deferred`.
+        wrapper_deferred.cancel()
+        self.assertNoResult(wrapper_deferred)
+        self.assertFalse(
+            deferred.called, "Original `Deferred` was unexpectedly cancelled"
+        )
+
+        # Now make the original `Deferred` fail.
+        # The `Failure` must be consumed, otherwise unwanted tracebacks will be printed
+        # in logs.
+        deferred.errback(ValueError("abc"))
+        self.assertIsNone(deferred.result, "`Failure` was not consumed")
+
+        # Now that the original `Deferred` has failed, we should get a `CancelledError`.
+        self.failureResultOf(wrapper_deferred, CancelledError)
+
+    def test_suppresses_second_cancellation(self):
+        """Test that a second cancellation is suppressed.
+
+        Identical to `test_cancellation` except the new `Deferred` is cancelled twice.
+        """
+        deferred: "Deferred[str]" = Deferred()
+        wrapper_deferred = delay_cancellation(deferred)
+
+        # Cancel the new `Deferred`, twice.
+        wrapper_deferred.cancel()
+        wrapper_deferred.cancel()
+        self.assertNoResult(wrapper_deferred)
+        self.assertFalse(
+            deferred.called, "Original `Deferred` was unexpectedly cancelled"
         )
 
-        # Now make the inner `Deferred` fail.
+        # Now make the original `Deferred` fail.
         # The `Failure` must be consumed, otherwise unwanted tracebacks will be printed
         # in logs.
         deferred.errback(ValueError("abc"))
         self.assertIsNone(deferred.result, "`Failure` was not consumed")
+
+        # Now that the original `Deferred` has failed, we should get a `CancelledError`.
+        self.failureResultOf(wrapper_deferred, CancelledError)
+
+    def test_propagates_cancelled_error(self):
+        """Test that a `CancelledError` from the original `Deferred` gets propagated."""
+        deferred: "Deferred[str]" = Deferred()
+        wrapper_deferred = delay_cancellation(deferred)
+
+        # Fail the original `Deferred` with a `CancelledError`.
+        cancelled_error = CancelledError()
+        deferred.errback(cancelled_error)
+
+        # The new `Deferred` should fail with exactly the same `CancelledError`.
+        self.assertTrue(wrapper_deferred.called)
+        self.assertIs(cancelled_error, self.failureResultOf(wrapper_deferred).value)
+
+    def test_preserves_logcontext(self):
+        """Test that logging contexts are preserved."""
+        blocking_d: "Deferred[None]" = Deferred()
+
+        async def inner():
+            await make_deferred_yieldable(blocking_d)
+
+        async def outer():
+            with LoggingContext("c") as c:
+                try:
+                    await delay_cancellation(defer.ensureDeferred(inner()))
+                    self.fail("`CancelledError` was not raised")
+                except CancelledError:
+                    self.assertEqual(c, current_context())
+                    # Succeed with no error, unless the logging context is wrong.
+
+        # Run and block inside `inner()`.
+        d = defer.ensureDeferred(outer())
+        self.assertEqual(SENTINEL_CONTEXT, current_context())
+
+        d.cancel()
+
+        # Now unblock. `outer()` will consume the `CancelledError` and check the
+        # logging context.
+        blocking_d.callback(None)
+        self.successResultOf(d)
diff --git a/tests/util/test_rwlock.py b/tests/util/test_rwlock.py
index 0774625b8551..0c842261971f 100644
--- a/tests/util/test_rwlock.py
+++ b/tests/util/test_rwlock.py
@@ -12,8 +12,10 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import AsyncContextManager, Callable, Sequence, Tuple
+
 from twisted.internet import defer
-from twisted.internet.defer import Deferred
+from twisted.internet.defer import CancelledError, Deferred
 
 from synapse.util.async_helpers import ReadWriteLock
 
@@ -21,87 +23,187 @@
 
 
 class ReadWriteLockTestCase(unittest.TestCase):
-    def _assert_called_before_not_after(self, lst, first_false):
-        for i, d in enumerate(lst[:first_false]):
-            self.assertTrue(d.called, msg="%d was unexpectedly false" % i)
+    def _start_reader_or_writer(
+        self,
+        read_or_write: Callable[[str], AsyncContextManager],
+        key: str,
+        return_value: str,
+    ) -> Tuple["Deferred[str]", "Deferred[None]", "Deferred[None]"]:
+        """Starts a reader or writer which acquires the lock, blocks, then completes.
+
+        Args:
+            read_or_write: A function returning a context manager for a lock.
+                Either a bound `ReadWriteLock.read` or `ReadWriteLock.write`.
+            key: The key to read or write.
+            return_value: A string that the reader or writer will resolve with when
+                done.
+
+        Returns:
+            A tuple of three `Deferred`s:
+             * A `Deferred` that resolves with `return_value` once the reader or writer
+               completes successfully.
+             * A `Deferred` that resolves once the reader or writer acquires the lock.
+             * A `Deferred` that blocks the reader or writer. Must be resolved by the
+               caller to allow the reader or writer to release the lock and complete.
+        """
+        acquired_d: "Deferred[None]" = Deferred()
+        unblock_d: "Deferred[None]" = Deferred()
+
+        async def reader_or_writer():
+            async with read_or_write(key):
+                acquired_d.callback(None)
+                await unblock_d
+            return return_value
+
+        d = defer.ensureDeferred(reader_or_writer())
+        return d, acquired_d, unblock_d
+
+    def _start_blocking_reader(
+        self, rwlock: ReadWriteLock, key: str, return_value: str
+    ) -> Tuple["Deferred[str]", "Deferred[None]", "Deferred[None]"]:
+        """Starts a reader which acquires the lock, blocks, then releases the lock.
+
+        See the docstring for `_start_reader_or_writer` for details about the arguments
+        and return values.
+        """
+        return self._start_reader_or_writer(rwlock.read, key, return_value)
+
+    def _start_blocking_writer(
+        self, rwlock: ReadWriteLock, key: str, return_value: str
+    ) -> Tuple["Deferred[str]", "Deferred[None]", "Deferred[None]"]:
+        """Starts a writer which acquires the lock, blocks, then releases the lock.
+
+        See the docstring for `_start_reader_or_writer` for details about the arguments
+        and return values.
+        """
+        return self._start_reader_or_writer(rwlock.write, key, return_value)
+
+    def _start_nonblocking_reader(
+        self, rwlock: ReadWriteLock, key: str, return_value: str
+    ) -> Tuple["Deferred[str]", "Deferred[None]"]:
+        """Starts a reader which acquires the lock, then releases it immediately.
+
+        See the docstring for `_start_reader_or_writer` for details about the arguments.
+
+        Returns:
+            A tuple of two `Deferred`s:
+             * A `Deferred` that resolves with `return_value` once the reader completes
+               successfully.
+             * A `Deferred` that resolves once the reader acquires the lock.
+        """
+        d, acquired_d, unblock_d = self._start_reader_or_writer(
+            rwlock.read, key, return_value
+        )
+        unblock_d.callback(None)
+        return d, acquired_d
+
+    def _start_nonblocking_writer(
+        self, rwlock: ReadWriteLock, key: str, return_value: str
+    ) -> Tuple["Deferred[str]", "Deferred[None]"]:
+        """Starts a writer which acquires the lock, then releases it immediately.
+
+        See the docstring for `_start_reader_or_writer` for details about the arguments.
+
+        Returns:
+            A tuple of two `Deferred`s:
+             * A `Deferred` that resolves with `return_value` once the writer completes
+               successfully.
+             * A `Deferred` that resolves once the writer acquires the lock.
+        """
+        d, acquired_d, unblock_d = self._start_reader_or_writer(
+            rwlock.write, key, return_value
+        )
+        unblock_d.callback(None)
+        return d, acquired_d
+
+    def _assert_first_n_resolved(
+        self, deferreds: Sequence["defer.Deferred[None]"], n: int
+    ) -> None:
+        """Assert that exactly the first n `Deferred`s in the given list are resolved.
 
-        for i, d in enumerate(lst[first_false:]):
+        Args:
+            deferreds: The list of `Deferred`s to be checked.
+            n: The number of `Deferred`s at the start of `deferreds` that should be
+                resolved.
+        """
+        for i, d in enumerate(deferreds[:n]):
+            self.assertTrue(d.called, msg="deferred %d was unexpectedly unresolved" % i)
+
+        for i, d in enumerate(deferreds[n:]):
             self.assertFalse(
-                d.called, msg="%d was unexpectedly true" % (i + first_false)
+                d.called, msg="deferred %d was unexpectedly resolved" % (i + n)
             )
 
     def test_rwlock(self):
         rwlock = ReadWriteLock()
-
-        key = object()
+        key = "key"
 
         ds = [
-            rwlock.read(key),  # 0
-            rwlock.read(key),  # 1
-            rwlock.write(key),  # 2
-            rwlock.write(key),  # 3
-            rwlock.read(key),  # 4
-            rwlock.read(key),  # 5
-            rwlock.write(key),  # 6
+            self._start_blocking_reader(rwlock, key, "0"),
+            self._start_blocking_reader(rwlock, key, "1"),
+            self._start_blocking_writer(rwlock, key, "2"),
+            self._start_blocking_writer(rwlock, key, "3"),
+            self._start_blocking_reader(rwlock, key, "4"),
+            self._start_blocking_reader(rwlock, key, "5"),
+            self._start_blocking_writer(rwlock, key, "6"),
         ]
-        ds = [defer.ensureDeferred(d) for d in ds]
+        # `Deferred`s that resolve when each reader or writer acquires the lock.
+        acquired_ds = [acquired_d for _, acquired_d, _ in ds]
+        # `Deferred`s that will trigger the release of locks when resolved.
+        release_ds = [release_d for _, _, release_d in ds]
 
-        self._assert_called_before_not_after(ds, 2)
+        # The first two readers should acquire their locks.
+        self._assert_first_n_resolved(acquired_ds, 2)
 
-        with ds[0].result:
-            self._assert_called_before_not_after(ds, 2)
-        self._assert_called_before_not_after(ds, 2)
+        # Release one of the read locks. The next writer should not acquire the lock,
+        # because there is another reader holding the lock.
+        self._assert_first_n_resolved(acquired_ds, 2)
+        release_ds[0].callback(None)
+        self._assert_first_n_resolved(acquired_ds, 2)
 
-        with ds[1].result:
-            self._assert_called_before_not_after(ds, 2)
-        self._assert_called_before_not_after(ds, 3)
+        # Release the other read lock. The next writer should acquire the lock.
+        self._assert_first_n_resolved(acquired_ds, 2)
+        release_ds[1].callback(None)
+        self._assert_first_n_resolved(acquired_ds, 3)
 
-        with ds[2].result:
-            self._assert_called_before_not_after(ds, 3)
-        self._assert_called_before_not_after(ds, 4)
+        # Release the write lock. The next writer should acquire the lock.
+        self._assert_first_n_resolved(acquired_ds, 3)
+        release_ds[2].callback(None)
+        self._assert_first_n_resolved(acquired_ds, 4)
 
-        with ds[3].result:
-            self._assert_called_before_not_after(ds, 4)
-        self._assert_called_before_not_after(ds, 6)
+        # Release the write lock. The next two readers should acquire locks.
+        self._assert_first_n_resolved(acquired_ds, 4)
+        release_ds[3].callback(None)
+        self._assert_first_n_resolved(acquired_ds, 6)
 
-        with ds[5].result:
-            self._assert_called_before_not_after(ds, 6)
-        self._assert_called_before_not_after(ds, 6)
+        # Release one of the read locks. The next writer should not acquire the lock,
+        # because there is another reader holding the lock.
+        self._assert_first_n_resolved(acquired_ds, 6)
+        release_ds[5].callback(None)
+        self._assert_first_n_resolved(acquired_ds, 6)
 
-        with ds[4].result:
-            self._assert_called_before_not_after(ds, 6)
-        self._assert_called_before_not_after(ds, 7)
+        # Release the other read lock. The next writer should acquire the lock.
+        self._assert_first_n_resolved(acquired_ds, 6)
+        release_ds[4].callback(None)
+        self._assert_first_n_resolved(acquired_ds, 7)
 
-        with ds[6].result:
-            pass
+        # Release the write lock.
+        release_ds[6].callback(None)
 
-        d = defer.ensureDeferred(rwlock.write(key))
-        self.assertTrue(d.called)
-        with d.result:
-            pass
+        # Acquire and release the write and read locks one last time for good measure.
+        _, acquired_d = self._start_nonblocking_writer(rwlock, key, "last writer")
+        self.assertTrue(acquired_d.called)
 
-        d = defer.ensureDeferred(rwlock.read(key))
-        self.assertTrue(d.called)
-        with d.result:
-            pass
+        _, acquired_d = self._start_nonblocking_reader(rwlock, key, "last reader")
+        self.assertTrue(acquired_d.called)
 
     def test_lock_handoff_to_nonblocking_writer(self):
         """Test a writer handing the lock to another writer that completes instantly."""
         rwlock = ReadWriteLock()
         key = "key"
 
-        unblock: "Deferred[None]" = Deferred()
-
-        async def blocking_write():
-            with await rwlock.write(key):
-                await unblock
-
-        async def nonblocking_write():
-            with await rwlock.write(key):
-                pass
-
-        d1 = defer.ensureDeferred(blocking_write())
-        d2 = defer.ensureDeferred(nonblocking_write())
+        d1, _, unblock = self._start_blocking_writer(rwlock, key, "write 1 completed")
+        d2, _ = self._start_nonblocking_writer(rwlock, key, "write 2 completed")
         self.assertFalse(d1.called)
         self.assertFalse(d2.called)
 
@@ -111,5 +213,182 @@ async def nonblocking_write():
         self.assertTrue(d2.called)
 
         # The `ReadWriteLock` should operate as normal.
-        d3 = defer.ensureDeferred(nonblocking_write())
+        d3, _ = self._start_nonblocking_writer(rwlock, key, "write 3 completed")
         self.assertTrue(d3.called)
+
+    def test_cancellation_while_holding_read_lock(self):
+        """Test cancellation while holding a read lock.
+
+        A waiting writer should be given the lock when the reader holding the lock is
+        cancelled.
+        """
+        rwlock = ReadWriteLock()
+        key = "key"
+
+        # 1. A reader takes the lock and blocks.
+        reader_d, _, _ = self._start_blocking_reader(rwlock, key, "read completed")
+
+        # 2. A writer waits for the reader to complete.
+        writer_d, _ = self._start_nonblocking_writer(rwlock, key, "write completed")
+        self.assertFalse(writer_d.called)
+
+        # 3. The reader is cancelled.
+        reader_d.cancel()
+        self.failureResultOf(reader_d, CancelledError)
+
+        # 4. The writer should take the lock and complete.
+        self.assertTrue(
+            writer_d.called, "Writer is stuck waiting for a cancelled reader"
+        )
+        self.assertEqual("write completed", self.successResultOf(writer_d))
+
+    def test_cancellation_while_holding_write_lock(self):
+        """Test cancellation while holding a write lock.
+
+        A waiting reader should be given the lock when the writer holding the lock is
+        cancelled.
+        """
+        rwlock = ReadWriteLock()
+        key = "key"
+
+        # 1. A writer takes the lock and blocks.
+        writer_d, _, _ = self._start_blocking_writer(rwlock, key, "write completed")
+
+        # 2. A reader waits for the writer to complete.
+        reader_d, _ = self._start_nonblocking_reader(rwlock, key, "read completed")
+        self.assertFalse(reader_d.called)
+
+        # 3. The writer is cancelled.
+        writer_d.cancel()
+        self.failureResultOf(writer_d, CancelledError)
+
+        # 4. The reader should take the lock and complete.
+        self.assertTrue(
+            reader_d.called, "Reader is stuck waiting for a cancelled writer"
+        )
+        self.assertEqual("read completed", self.successResultOf(reader_d))
+
+    def test_cancellation_while_waiting_for_read_lock(self):
+        """Test cancellation while waiting for a read lock.
+
+        Tests that cancelling a waiting reader:
+         * does not cancel the writer it is waiting on
+         * does not cancel the next writer waiting on it
+         * does not allow the next writer to acquire the lock before an earlier writer
+           has finished
+         * does not keep the next writer waiting indefinitely
+
+        These correspond to the asserts with explicit messages.
+        """
+        rwlock = ReadWriteLock()
+        key = "key"
+
+        # 1. A writer takes the lock and blocks.
+        writer1_d, _, unblock_writer1 = self._start_blocking_writer(
+            rwlock, key, "write 1 completed"
+        )
+
+        # 2. A reader waits for the first writer to complete.
+        #    This reader will be cancelled later.
+        reader_d, _ = self._start_nonblocking_reader(rwlock, key, "read completed")
+        self.assertFalse(reader_d.called)
+
+        # 3. A second writer waits for both the first writer and the reader to complete.
+        writer2_d, _ = self._start_nonblocking_writer(rwlock, key, "write 2 completed")
+        self.assertFalse(writer2_d.called)
+
+        # 4. The waiting reader is cancelled.
+        #    Neither of the writers should be cancelled.
+        #    The second writer should still be waiting, but only on the first writer.
+        reader_d.cancel()
+        self.failureResultOf(reader_d, CancelledError)
+        self.assertFalse(writer1_d.called, "First writer was unexpectedly cancelled")
+        self.assertFalse(
+            writer2_d.called,
+            "Second writer was unexpectedly cancelled or given the lock before the "
+            "first writer finished",
+        )
+
+        # 5. Unblock the first writer, which should complete.
+        unblock_writer1.callback(None)
+        self.assertEqual("write 1 completed", self.successResultOf(writer1_d))
+
+        # 6. The second writer should take the lock and complete.
+        self.assertTrue(
+            writer2_d.called, "Second writer is stuck waiting for a cancelled reader"
+        )
+        self.assertEqual("write 2 completed", self.successResultOf(writer2_d))
+
+    def test_cancellation_while_waiting_for_write_lock(self):
+        """Test cancellation while waiting for a write lock.
+
+        Tests that cancelling a waiting writer:
+         * does not cancel the reader or writer it is waiting on
+         * does not cancel the next writer waiting on it
+         * does not allow the next writer to acquire the lock before an earlier reader
+           and writer have finished
+         * does not keep the next writer waiting indefinitely
+
+        These correspond to the asserts with explicit messages.
+        """
+        rwlock = ReadWriteLock()
+        key = "key"
+
+        # 1. A reader takes the lock and blocks.
+        reader_d, _, unblock_reader = self._start_blocking_reader(
+            rwlock, key, "read completed"
+        )
+
+        # 2. A writer waits for the reader to complete.
+        writer1_d, _, unblock_writer1 = self._start_blocking_writer(
+            rwlock, key, "write 1 completed"
+        )
+
+        # 3. A second writer waits for both the reader and first writer to complete.
+        #    This writer will be cancelled later.
+        writer2_d, _ = self._start_nonblocking_writer(rwlock, key, "write 2 completed")
+        self.assertFalse(writer2_d.called)
+
+        # 4. A third writer waits for the second writer to complete.
+        writer3_d, _ = self._start_nonblocking_writer(rwlock, key, "write 3 completed")
+        self.assertFalse(writer3_d.called)
+
+        # 5. The second writer is cancelled, but continues waiting for the lock.
+        #    The reader, first writer and third writer should not be cancelled.
+        #    The first writer should still be waiting on the reader.
+        #    The third writer should still be waiting on the second writer.
+        writer2_d.cancel()
+        self.assertNoResult(writer2_d)
+        self.assertFalse(reader_d.called, "Reader was unexpectedly cancelled")
+        self.assertFalse(writer1_d.called, "First writer was unexpectedly cancelled")
+        self.assertFalse(
+            writer3_d.called,
+            "Third writer was unexpectedly cancelled or given the lock before the first "
+            "writer finished",
+        )
+
+        # 6. Unblock the reader, which should complete.
+        #    The first writer should be given the lock and block.
+        #    The third writer should still be waiting on the second writer.
+        unblock_reader.callback(None)
+        self.assertEqual("read completed", self.successResultOf(reader_d))
+        self.assertNoResult(writer2_d)
+        self.assertFalse(
+            writer3_d.called,
+            "Third writer was unexpectedly given the lock before the first writer "
+            "finished",
+        )
+
+        # 7. Unblock the first writer, which should complete.
+        unblock_writer1.callback(None)
+        self.assertEqual("write 1 completed", self.successResultOf(writer1_d))
+
+        # 8. The second writer should take the lock and release it immediately, since it
+        #    has been cancelled.
+        self.failureResultOf(writer2_d, CancelledError)
+
+        # 9. The third writer should take the lock and complete.
+        self.assertTrue(
+            writer3_d.called, "Third writer is stuck waiting for a cancelled writer"
+        )
+        self.assertEqual("write 3 completed", self.successResultOf(writer3_d))
diff --git a/tox.ini b/tox.ini
index 04b972e2c58c..3ffd2c3e97e8 100644
--- a/tox.ini
+++ b/tox.ini
@@ -38,21 +38,10 @@ lint_targets =
     setup.py
     synapse
     tests
-    scripts
     # annoyingly, black doesn't find these so we have to list them
-    scripts/export_signing_key
-    scripts/generate_config
-    scripts/generate_log_config
-    scripts/hash_password
-    scripts/register_new_matrix_user
-    scripts/synapse_port_db
-    scripts/update_synapse_database
     scripts-dev
-    scripts-dev/build_debian_packages
-    scripts-dev/sign_json
     stubs
     contrib
-    synctl
     synmark
     .ci
     docker
@@ -162,38 +151,11 @@ extras = lint
 commands =
     python -m black --check --diff {[base]lint_targets}
     flake8 {[base]lint_targets} {env:PEP8SUFFIX:}
-    {toxinidir}/scripts-dev/config-lint.sh
 
 [testenv:check_isort]
 extras = lint
 commands = isort -c --df {[base]lint_targets}
 
-[testenv:combine]
-skip_install = true
-usedevelop = false
-deps =
-    coverage
-    pip>=10
-commands=
-    coverage combine
-    coverage report
-
-[testenv:cov-erase]
-skip_install = true
-usedevelop = false
-deps =
-    coverage
-commands=
-    coverage erase
-
-[testenv:cov-html]
-skip_install = true
-usedevelop = false
-deps =
-    coverage
-commands=
-    coverage html
-
 [testenv:mypy]
 deps =
     {[base]deps}