[lexical-yjs] Bug Fix: handle text node being split by Yjs redo

[james-atticus]

Description

Fixes a bug in applyChildrenYjsDelta which caused Lexical and Yjs to get out of sync. Once in this state, some changes would not sync to other clients; the changes would be lost on refresh.

This can be reproduced in the Playground with the following steps:

1. In the left editor, type "Hello World"
2. Select "World" and change the formatting to bold
3. In the right editor, type a character in the middle of "World", eg "Wor_ld"
4. In the left editor, click undo then redo
5. Any text added at the end in the left editor won't be synced to the right editor

When applying change deltas from Yjs, an insertDelta can be a string or a sharedType. If currIndex is pointing to some position within a text node and insertDelta is a string, then the new text is spliced in correctly. If insertDelta represents a shared type, then the newly created collabNode is inserted in the wrong position (before said text node).

This PR updates the logic in applyChildrenYjsDelta to handle inserting a sharedType node in the middle of a text node.

Test plan

The repro steps above are covered in an end-to-end test. I added a second E2E test to cover the case where the first insertDelta corresponds to an ElementNode, then the second delta is the TextNode.

Before

Lexical.applyChildrenYjsDelta.before.mov

After

Lexical.applyChildrenYjsDelta.after.mov

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
lexical	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jan 26, 2025 10:28am
lexical-playground	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jan 26, 2025 10:28am

[github-actions]

size-limit report 📦

Path	Size
lexical - cjs	29.07 KB (0%)
lexical - esm	28.86 KB (0%)
@lexical/rich-text - cjs	38.04 KB (0%)
@lexical/rich-text - esm	30.92 KB (0%)
@lexical/plain-text - cjs	36.55 KB (0%)
@lexical/plain-text - esm	28.22 KB (0%)
@lexical/react - cjs	39.85 KB (0%)
@lexical/react - esm	32.28 KB (0%)

[etrepum]

I haven't done an audit of exactly how this works but it seems unlikely to be problematic given that it passes the existing e2e suite and the new test. Locally the change looks like it makes sense.