[zurfyx]

Note

Stack, part 3 of 10. Based on #9523 (zurfyx/write-before-unread-change). Review only this PR's own commits.

The @lexical/y fixes touch the same writer, cursor, reader and binding internals, so they are one linear stack: each PR is based on the one below it, each conflict is resolved once, in the PR whose change causes it, and every CI run tests the real combination.

Merge order: bottom first, #9509 → #9523 → #9522 → #9505 → #9508 → #9502 → #9504 → #9527 → #9507 → #9510. With squash merges, rebase the next PR onto main before merging it (git rebase --onto main <old base branch>).

The stack

#	PR	Branch	Base
1	#9509	zurfyx/update-error-rollback	main
2	#9523	zurfyx/write-before-unread-change	#9509
3	#9522 (this PR)	zurfyx/y-keep-chars-at-format-boundary	#9523
4	#9505	zurfyx/y-undo-member-closer	#9522
5	#9508	zurfyx/y-initial-state-binding	#9505
6	#9502	zurfyx/y-reorder-intent	#9508
7	#9504	zurfyx/y-preserve-unknown-attrs	#9502
8	#9527	zurfyx/y-move-keeps-unknown-fields	#9504
9	#9507	zurfyx/y-composition-holdback	#9527
10	#9510	zurfyx/y-incremental-read-marks	#9507

Follow-ups for after the stack (not in it):

• One "seen of Yjs" view. [lexical-y] Bug Fix: Write a local update made before an unread remote change on the document it was made on #9523's Unread (changes Yjs applied that the binding has not read) and [lexical-playground][lexical-website][lexical-y] Bug Fix: Hold back remote changes to the line being composed until the composition ends #9507's Hidden (changes held back while a line is composed) answer one question, and call sites combine them by hand. One owner module (isGone, isShown, attrOf/attrsOf and the write primitives), an item-level held overlay instead of the was/now maps, and a lint or grep test that allows raw .deleted/getAttr(s) only in the Reader and in named provenance scans. [lexical-website][lexical-y] Bug Fix: Stop a format, comment or link from spreading to the end of the document after an undo or delete races an edit inside it #9505's run-opener scans (liveItemBefore, runOpener, restatedEnd) still read raw deletedness and move there too.
• B-2 at the end of a line. Enter at the very end of a line being composed, while a collaborator's alignment change is held back, leaves that alignment off the new line Lexical copies it to. Enter inside the line keeps it on both halves. It needs a per-key "inherits on split" rule, or a Limit in y.md.
• [lexical-website][lexical-y] Bug Fix: Keep the fields an older client does not know in a block it moves #9527's group fallback chain. A moved item takes its group's fields from a chain of four lookups ($groupReference, $priorGroupItem, the nearest neighbour's marker before the write, priorGroupMarker), with separate predecessor stores for markers and nodes. One stored-predecessor lookup would replace it.

Description

When a line's children are made again as one node with one word changed
(an agent's block rewrite), @lexical/y wrote some unchanged characters
again as new text, if the changed word had been a text node of its own (for
example italic). A collaborator's concurrent edit of that word then landed
inside the word before it, on every client:

• "t16z " | "t63z " | " t19z", rewritten as one plain node with
  t63z changed to t80z, wrote "z t80z " instead of "t80z ". A
  collaborator who replaced t63z with t83z at the same time got
  "t16t83zz t80z t19z".
• The same happens when the dropped node is the last one ("t58z t59z" |
  " t60z t61z" rewrote the z of t59z), and with an IME composition in
  the rewritten line.

The cause is in how a line's characters are matched. A removed node's text
is matched whole or not at all, so the italic "t63z " is deleted whole and
the old text is matched without it, as "t16z t19z". The final check keeps
only what a second diff, which takes the common end first, keeps too. Over
that shortened text, the second diff read the change as "z t80" inserted
inside t16z. It disagreed with the first diff about the z , and the
check dropped it.

The check now also reads the old text as it was, with the text deleted whole
still in place, wherever the shortened text left some out. A character
either reading keeps the same way is kept. The change can only keep more
than before, and only where a removed node's text was deleted whole.
Elsewhere the stored bytes are unchanged.

Restack (October 29)

Rebased onto #9523 with no conflicts. It adds no raw attribute or deletedness reads on the write path, so nothing here changes for #9523's view.

Changeset

.changeset/lexical-y-keep-chars-at-format-boundary.md: [fix] for
@lexical/y, with a Verify: paragraph.

Test plan

New regression cases in
packages/lexical-y/src/__tests__/unit/regressions/TextIdentity.test.ts:
three line shapes, each in both client orders. Each checks the rewrite's own
deleted and inserted text, and that the text before the changed node stays
whole on every client and in a fresh read.

Before

$ npx vitest --project unit --no-watch packages/lexical-y/src/__tests__/unit/regressions/TextIdentity.test.ts -t "S7-39"
 Test Files  1 failed (1)
      Tests  6 failed | 95 skipped (101)

AssertionError: expected { del: 'z t63z ', ins: 'z t80z ' } to deeply equal { del: 't63z ', ins: 't80z ' }
AssertionError: expected { del: ' cd ', ins: ' gh ' } to deeply equal { del: 'cd ', ins: 'gh ' }
-   "del": " t60z t61z",
-   "ins": " t70z t61z",
+   "del": "z t60z t61z",
+   "ins": "z t70z t61z",

After

$ npx vitest --project unit --no-watch packages/lexical-y/src/__tests__/unit/regressions/TextIdentity.test.ts -t "S7-39"
      Tests  6 passed | 95 skipped (101)

$ npx vitest --project unit --no-watch --maxWorkers=7 packages/lexical-y
 Test Files  148 passed | 2 skipped (150)
      Tests  4919 passed | 16 expected fail | 2 skipped (4937)

$ pnpm run ci-check
Changeset check passed: 5 pending changeset(s) valid.
Found 0 errors

I also ran randomized text-identity sessions from earlier reviews (a local
harness, not committed): 1,000 seeds of whole-node sets and swaps, 1,000 of
sets with made nodes, and 800 of plugin, agent and paste sessions. Every
summary and failure list matched main. The stored document state matched
main in all 783 sessions that are deterministic across two runs of main. A
replay of a randomized IME session that showed this bug (a composed word
landing inside the word before it) no longer does. Browser e2e was not
run.

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Project	Deployment	Actions	Updated
lexical	Ready	Preview	Oct 29, 2026 5:55pm UTC
lexical-playground	Ready	Preview	Oct 29, 2026 5:55pm UTC

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commit: f45dfa2