Fix: handle Delete merging with following paragraph after nested list…

[yyppsk]

What?

Closes #77245

Fixes forward Delete at the end of a nested list item so it correctly merges the following block (e.g. a paragraph) into the list.

Why?

When pressing Delete at the end of a nested list item, nothing happens if the next block is outside the list hierarchy (e.g. a paragraph after the list). This is because getNextId only searches within the list's own tree and returns undefined for nested items that are the last at every level, causing the code to fall through to onMerge( forward ), which itself has no effect since the list-item is not top-level.

Top-level list items already merge correctly with following blocks; only nested items are broken.

How?

Added a new helper getNextOuterBlockClientId in useMerge that, when getNextId returns nothing, walks up through ancestor list-items and checks whether any ancestor list has a next sibling block. If one is found, mergeBlocks is called between the ancestor list and that following block, which uses the existing __experimentalOnMerge merge path on core/list to absorb the block as new list items.

The fix is intentionally not guarded to only core/paragraph , the mergeBlocks codepath already handles non-convertible block types gracefully (it simply selects the first block without modifying anything), and top-level items already merge with any block type, so nested items should behave consistently.

Testing Instructions

1. Create a new post.
2. Add a List block with one outer item and one nested (indented) item.
3. Add a Paragraph block with some text after the list.
4. Place the cursor at the end of the nested item.
5. Press Delete.
6. Expected: The paragraph merges into the list as a new nested list item.
7. Before this fix: Nothing happened.

Testing Instructions for Keyboard

Same as above.

Screenshots or screencast

Before	After
Pressing Delete at the end of a nested list item does nothing	The following paragraph is merged into the nested list as a new item
Screen.Recording.2026-04-13.at.2.59.15.PM.mov	Screen.Recording.2026-04-13.at.2.55.36.PM.mov

Use of AI Tools

Claude was used to review the patch, evaluate correctness. All code was reviewed manually.

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[github-actions]

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[mikachan]

Thanks for working on this!

These changes look good, and they're testing well for me. I see you added some tests, but then reverted them. I think testing these changes would be a good idea, so I'd suggest adding some tests back before we merge this.

[yyppsk]

Thanks for working on this!

These changes look good, and they're testing well for me. I see you added some tests, but then reverted them. I think testing these changes would be a good idea, so I'd suggest adding some tests back before we merge this.

I’ve also included the reverted and improved tests in the new commit.t @mikachan .

[mikachan]

Thanks for the recent changes! I've spotted one other potential change in the test file.

[mcsf]

Thanks for the work here, @yyppsk!

There is one more edge case that this fix reveals, though. I wonder if we should fix it in this same PR or separately:

1. Have two separate consecutive List blocks (see the List View in the recording below)
2. Add a nested item in the first list
3. Try to Delete into the next list
4. Observed: No merge happens, but the nested List gets selected (confusing and prone to accidental deletion)

delete-into-sibling-list.mov