Notebook Timeline does not reflect true state of notebook & does not work as expected

[DonJayamanne]

Does this issue occur when all extensions are disabled?: Yes/No

• VS Code Version: OSS
• OS Version:

Steps to Reproduce:

1. Create a new notebook on disc, save it => First entry Create xx.ipynb
2. Add a new cell & save => Next entry edit
3. Add another cell & save => Next entry Insert Cell
4. Repeat this, a few times, and pause a few seconds before saving
   The items in the time line are

• Either edit or Insert Cell, seems to alternate
• Sometimes we end up with Update Cell Metadata as well
• Some times we do not have an entry in Timeline for the cell inserted, hence timeline is now completely wrong.

Problems

1. Create a new notebook and hit Ctrl+Save multiple times in quick succession and you'll end up with at least two Create xxx.ipynb in the timeline.

2. If we create 10 cells, I would expect to see 10 different entries in Timeline, this is not the case
   By design, also see pushStackElement API in Notebook Editor Model needs to line up with Text Editor  #207523

3. We seem to alternate between edit and Insert Cell
   Fixed pushStackElement API in NB Model to be same as same API in Text Model #207525

4. Clicking on one of the items such as edit entry in Timeline displays a broken editor (The editor could not be opened due to an unexpected error....)
   Filed here Unable to open notebook diff view from timeline (Leaking event listener) #207418
   If one of the edit works, then clicking another fails.
   This is very flaky, sometimes the edit entry that worked, no longer works at all.

5. Hitting save without making any changes results in either edit or Update Cell Metadata appearing in the timeline (ensure notebook format is 4.5)
   Whats weird is the fact that SCM view shows now difference.
   Create a notebok with a markdown cell
   Possible the notebook metadata diffing works based on Object refs
   Fixed Avoid unnecessary workspace edits #207377

6. Unwanted Update Cell Metadata entry
   This seems to be related to attachment changes.
   Also, for some reason this entry shows that the metadata is removed.

7. When you add a md cell
   We end up with one item edit and the diff view shows that the metadata of the md cell is removed.
   When in fact we should have an entry for Insert MD as mentioned earlier.
   A few issues here (metadata getting removed in diff view and missing entries)
   Fixed pushStackElement API in NB Model to be same as same API in Text Model #207525

8. Work on a notebook and add 10 cells and edit tyhem, etc
   Eventually use the key z to remove all the added cells (i.e. undo them all)
   Next Save and you'll end up with an Undo / Redo entry
   Clicking this item results in a completely broken view.

[DonJayamanne]

Closing as fixed.

[DonJayamanne]

Steps

• Open a workspace folder
• Create a Jupyter notebook
• Save this file
• Verify there's an entry in the timeline view for this notebook
• Save this file a few more times without making any changes
• Verify there are no new entries in the timeline view (previously we'd have one entry for each save operation)