Bug: [lexical-y] Undoing a delete of part of a word a collaborator's update made again with a word inserted inside it shows that part twice #9635

Lexical version: main at fcea4ff (@lexical/y), the 0.53.1-nightly.20261030.0 build (e28f4dd), and #9625.

Steps To Reproduce

1. Two clients bind one document whose line is one text node, aa bbcc dd.
2. Client A, offline, makes the node again from its JSON with a word inserted inside the word bbcc: aa bb xxcc dd (an agent rewriting a block).
3. Client B, offline, deletes aa bb (a range selection from the start of the line into bbcc), then undoes the delete.
4. The clients sync.

a.update(() => {
  const n = $getRoot().getFirstChildOrThrow<ElementNode>().getFirstChildOrThrow<TextNode>();
  n.replace($parseSerializedNode({...n.exportJSON(), text: 'aa bb xxcc dd'}));
});
b.update(() => {
  // select offsets 0..5 ("aa bb") of the line and removeText()
});
b.undo();
await sync();

The current behavior

Every client shows aa bbbb xxcc dd: bb twice. The same with both client id orders. With bb and cc separate words (aa bb cc dd made again as aa bb xx cc dd) it shows bb once on #9625 (on the nightly, twice there too).

An insertion between two letters of a word in text made again replaces that word whole (#9598, so that an edit computed before the rewrite that replaces the old word takes nothing out of the new one), so A deletes the old bbcc and writes bb xxcc. B's undo brings the bb it deleted back as new content, next to A's new bb: the same shape as two clients removing the same text and both undoing (D50 in packages/lexical-y/DECISIONS.md).

A related shape: if A undoes its rewrite instead while B deletes bb (aa b1zc2z dd made again as aa b1z x9zc2z dd, B deletes b1z, A undoes), A's undo brings the old word back as new content, B's delete included, and on some timings a stray character of the deleted word stays glued to the next one.

The expected behavior

bb once: aa bb xxcc dd.

Notes

Keeping the unchanged characters of a word changed by an insertion inside it would fix the duplicate but brings back the case the whole-word rule prevents (#9608: a stale replace of the old word taking a letter of the new one). Until a design covers both, the binding documents this next to "Text nodes made again with other text" in y.md's Limits.