feat: add undo and redo shortcuts for deleting blocks

[lavjeetrai]

Description

This PR upgrades the Ctrl+Z and Ctrl+Y keyboard shortcuts to support a generalized undo/redo history using the Command Pattern. Users can now flawlessly revert and reapply both block movements and block deletions.

Screen.Recording.2026-07-01.233456.mp4

Key Changes

• Action History Stack: Replaced the primitive trashStacks system with an actionHistory and redoActionHistory array in blocks.js to log generalized { type: "move" | "trash", ... } objects.

• Coordinate Tracking: Added mousedown coordinate tracking to record precise start/end locations of blocks when dragged across the canvas.

• Feature

[codecov]

Codecov Report

❌ Patch coverage is 61.42857% with 27 lines in your changes missing coverage. Please review.
✅ Project coverage is 54.19%. Comparing base (7dd8361) to head (7b8ddfa).
⚠️ Report is 35 commits behind head on master.

Files with missing lines	Patch %	Lines
js/blocks.js	69.49%	18 Missing ⚠️
js/activity.js	0.00%	7 Missing ⚠️
js/block.js	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7714      +/-   ##
==========================================
+ Coverage   54.12%   54.19%   +0.06%     
==========================================
  Files         172      172              
  Lines       57072    57133      +61     
==========================================
+ Hits        30892    30964      +72     
+ Misses      26180    26169      -11     

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[Chaitu7032]

the feature is working tested locally 👍. good work .

but Looks like sendStackToTrash() and restoreTrashById() already add the action to actionHistory. Do we also need this.actionHistory.push(action) here ? It seems like this could create duplicate history entries after redo.

[github-actions]

This PR has merge conflicts with master.

Please rebase your branch:

# Add upstream remote (one-time setup)
git remote add upstream https://github.com/sugarlabs/musicblocks.git

# Fetch latest master and rebase
git fetch upstream
git rebase upstream/master

# Resolve any conflicts, then:
git push --force-with-lease origin YOUR_BRANCH

Tip: Enable "Allow edits from maintainers" on this PR so we can auto-rebase for you next time. This only grants access to your PR branch. Your fork's other branches are not affected.

[lavjeetrai]

@Chaitu7032 thanks for this critical reveiw, i have fixed it ,now take a look .

[lavjeetrai]

@walterbender @zealot-zew what u guys think about this feature?

[walterbender]

I've not tested your code yet. Will do over the weekend. This has been tried numerous times but we've yet to strike the right balance in terms of what undo granularity should be. Each block movement? Only block movements that cause a connection change? Values in arg blocks? etc. I'd be curious as to how you determined what a change consists of.

[walterbender]

This does a good job as far as it goes. But one UX issue and a lot of questions.
My instinct was to repeatedly type ctrl-z to restore multiple changes. But it seems that I could only type one at a time and wait for the message to appear each time. Is there a reason for that?
When restoring from the trash, the block was restored but not put back to the same position it was deleted from.

I would expect to see changes in block values restored as well: if I change a pitch, ctrl-z says "nothing to do."

[lavjeetrai]

Thanks for the feedback! @walterbender

Regarding the Ctrl+Z UX issue, there wasn't any specific reason behind requiring users to wait between consecutive undo operations. I'll look into improving that behavior so multiple undo actions can be triggered seamlessly.

I'll also start working on the other points you mentioned, including restoring deleted blocks to their original position and supporting undo for block value changes, and I'll update the PR as I make progress.

[stutijain2006]

Hi @lavjeetrai
I raised a PR long time back adding undo redo functionality only in three major cases - out of which one was deleting a block as well, and it was working perfectly fine in all cases and in collaboration with restore from stack as well, you can have a look, and it adds undo/redo to block addition and movement as well. It was closed due to inactivity for 60 days.

#4903

[stutijain2006]

Hi @lavjeetrai I raised a PR long time back adding undo redo functionality only in three major cases - out of which one was deleting a block as well, and it was working perfectly fine in all cases and in collaboration with restore from stack as well, you can have a look, and it adds undo/redo to block addition and movement as well. It was closed due to inactivity for 60 days.

#4903

There was only one bug in that PR that adding a new block directly in the existing block and undo that leads to white space. This issue is mentioned in the comments of that PR as well. So if you wish to work on that PR, you can do that, I will merge your commits into the same.

[lavjeetrai]

Hi @stutijain2006, thanks for letting me know and for sharing your PR!

Sorry, but I'm already familiar with the implementation in my current PR, and I don't have enough time to go through the older PR in detail. I think it's more efficient for me to continue with my current approach.

That said, since you've already worked on this, I'd really appreciate your help if I run into any issues or need guidance while finishing it.

Sorry and Thanks again!

[stutijain2006]

Hi @stutijain2006, thanks for letting me know and for sharing your PR!

Sorry, but I'm already familiar with the implementation in my current PR, and I don't have enough time to go through the older PR in detail. I think it's more efficient for me to continue with my current approach.

That said, since you've already worked on this, I'd really appreciate your help if I run into any issues or need guidance while finishing it.

Sorry and Thanks again!

That's completely fine. No issues. Keep on working on your PR, and can ask me for help if you face any difficult in between.