diff --git a/packages/cosmic-swingset/bin/ag-solo-xs.js b/packages/cosmic-swingset/bin/ag-solo-xs.js
index b6f1060142d..82009d054e6 100644
--- a/packages/cosmic-swingset/bin/ag-solo-xs.js
+++ b/packages/cosmic-swingset/bin/ag-solo-xs.js
@@ -34,7 +34,7 @@ export default async function main() {
   for (const [internal, external] of Object.entries(native)) {
     cmap[internal] = Compartment.map[external];
   }
-  const endowments = { console, require, setImmediate, setInterval, URL };
+  const endowments = { console, require, setImmediate, setInterval, setTimeout, URL };
 
   try {
     // console.log('making compartment...');
diff --git a/packages/cosmic-swingset/lib/xs-node-api/fs.js b/packages/cosmic-swingset/lib/xs-node-api/fs.js
index 1b66c732225..2e015f81974 100644
--- a/packages/cosmic-swingset/lib/xs-node-api/fs.js
+++ b/packages/cosmic-swingset/lib/xs-node-api/fs.js
@@ -9,19 +9,18 @@ export function makePathAccess(path) {
   return makePath(path, { File, Iterator });
 }
 
+const mkp = makePathAccess;
+
 function readFileSync(path) {
-  const p = makePath(path, { File, Iterator });
-  return p.readFileSync();
+  return mkp(path).readFileSync();
 }
 
-function readdirSync(path) {
-  const p = makePath(path, { File, Iterator });
-  return p.readdirSync();
+function readdirSync(path, options) {
+  return mkp(path).readdirSync(options);
 }
 
 function statSync(path) {
-  const p = makePath(path, { File, Iterator });
-  return p.statSync();
+  return mkp(path).statSync();
 }
 
 export function realpathSync(path) {
@@ -59,26 +58,36 @@ const openFiles = (() => {
 })();
 
 function later(thunk) {
-  Promise.resolve(null).then(thunk);
+  return new Promise((resolve, reject) => {
+    try {
+      resolve(thunk());
+    } catch (err) {
+      reject(err);
+    }
+  });
 }
 
 const promises = harden({
+  readFile(path) {
+    return mkp(path).readFile();
+  },
+  writeFile(file, data) {
+    return mkp(file).writeFile(data);
+  },
   write(fd, text) {
-    later(() => {
-      openFiles.lookup(fd).write(text);
-    });
+    return later(() => openFiles.lookup(fd).write(text));
   },
   close(fd) {
-    later(() => openFiles.close(fd));
+    return later(() => openFiles.close(fd));
   },
   readdir(path) {
-    return makePath(path, { File, Iterator }).readdir();
+    return mkp(path).readdir();
   },
   rename(from, to) {
-    later(() => File.rename(from, to));
+    return later(() => File.rename(from, to));
   },
   unlink(path) {
-    later(() => File.delete(path));
+    return later(() => File.delete(path));
   },
 });
 
@@ -97,6 +106,7 @@ export function openSync(path, mode = 'r') {
       throw new Error('already exists');
     } catch (_doesNotExist) {
       // ok
+      // ISSUE: need to distinguish doesNotExist from no permission etc.?
     }
     return openFiles.add(path, true);
   }
diff --git a/packages/cosmic-swingset/lib/xs-node-api/pathlib.js b/packages/cosmic-swingset/lib/xs-node-api/pathlib.js
index 3b6de2e9f86..69e45a83bf8 100644
--- a/packages/cosmic-swingset/lib/xs-node-api/pathlib.js
+++ b/packages/cosmic-swingset/lib/xs-node-api/pathlib.js
@@ -33,6 +33,16 @@ export function join(...paths) {
   return normalize(paths.join('/'));
 }
 
+function later(thunk) {
+  return new Promise((resolve, reject) => {
+    try {
+      resolve(thunk());
+    } catch (err) {
+      reject(err);
+    }
+  });
+}
+
 export function makePath(filename, { File, Iterator }) {
   const mk = there => makePath(there, { File, Iterator });
 
@@ -74,46 +84,37 @@ export function makePath(filename, { File, Iterator }) {
   }
 
   function atomicReplace(contents) {
-    return new Promise((resolve, reject) => {
-      try {
-        const tmp = mk(`${filename}.tmp`);
-        const tmpF = new File(tmp, true);
-        tmpF.write(contents);
-        tmpF.close();
-        File.rename(tmp, filename);
-      } catch (oops) {
-        reject(oops);
-        return;
-      }
-      resolve();
+    return later(() => {
+      const tmp = mk(`${filename}.tmp`);
+      const tmpF = new File(tmp, true);
+      tmpF.write(contents);
+      tmpF.close();
+      File.rename(tmp, filename);
     });
   }
 
-  function readdirSync(options) {
+  function readdirSync(options = {}) {
     const dirIter = new Iterator(filename);
     let item;
     const items = [];
     while ((item = dirIter.next())) {
-      const f = typeof item.length === 'number';
-      items.push(
-        harden({
-          name: item.name,
-          isFile: () => f,
-        }),
-      );
+      if (options.withFileTypes) {
+        const f = typeof item.length === 'number';
+        items.push(
+          harden({
+            name: item.name,
+            isFile: () => f,
+          }),
+        );
+      } else {
+        items.push(item.name);
+      }
     }
     return items;
   }
 
-  function readdir() {
-    return new Promise((resolve, reject) => {
-      try {
-        const names = readdirSync({}).map(item => item.name);
-        resolve(names);
-      } catch (oops) {
-        reject(oops);
-      }
-    });
+  function readdir(options) {
+    return later(() => readdirSync(options));
   }
 
   function butLast(p) {
@@ -166,6 +167,9 @@ export function makePath(filename, { File, Iterator }) {
     exists,
     statSync,
     readFileSync,
+    readFile() {
+      return later(() => readFileSync());
+    },
     readlinesSync() {
       const text = readFileSync();
       if (text === '') {
@@ -177,6 +181,12 @@ export function makePath(filename, { File, Iterator }) {
     readdir,
     bundleSource,
     atomicReplace,
+    writeFile(data, options) {
+      return later(() => {
+        const f = new File(filename, true);
+        f.write(data);
+      });
+    },
     withWriting,
   });
 }
diff --git a/packages/cosmic-swingset/lib/xs-npm/deterministic-json.js b/packages/cosmic-swingset/lib/xs-npm/deterministic-json.js
index 8b49f2a41b7..1159b061277 100644
--- a/packages/cosmic-swingset/lib/xs-npm/deterministic-json.js
+++ b/packages/cosmic-swingset/lib/xs-npm/deterministic-json.js
@@ -1,3 +1,4 @@
-export default function () {
-  throw 'TODO!';
-}
+// ISSUE: why are we using deterministic-json? Are we using the buffer stuff?
+import stringify from '@agoric/swingset-vat/src/kernel/json-stable-stringify';
+
+export default { stringify };