[zurfyx]

Description

Follow-ups to #9607 from the review bot:

• SUPPORTED_YJS_VERSION was published as a literal type
  (export declare const SUPPORTED_YJS_VERSION = "14.0.0-rc.29"), so its
  TypeScript type changed with every @y/y bump, while the Flow
  declaration says string. It is now declared string, as
  LEXICAL_VERSION is; scripts/updateVersion.mjs matches the new form
  when it regenerates the literal.
• The playground pins @y/y on its own (packages/lexical-playground),
  and nothing in the workspace ties it to @lexical/y's pin, so a bump
  that missed it would leave the playground's document and its provider on
  two copies of Yjs. The README's "Bumping @y/y" checklist names it, and
  YjsContract.test.ts now fails when the playground's pin differs from
  SUPPORTED_YJS_VERSION.

Changeset

None: SUPPORTED_YJS_VERSION keeps its value and is part of the unreleased
feature #9607's changeset already describes; the rest is docs, a test and
tooling.

Test plan

Before

The emitted declaration:

export declare const SUPPORTED_YJS_VERSION = "14.0.0-rc.29";

The new assertion with the playground's pin set to 14.0.0-rc.28:

× is the exact @y/y peer dependency, the dev dependency and the installed @y/y
AssertionError: expected '14.0.0-rc.28' to be '14.0.0-rc.29'

After

export declare const SUPPORTED_YJS_VERSION: string;

$ node scripts/updateVersion.mjs   # literal set to '0.0.0-stale' first
export const SUPPORTED_YJS_VERSION: string = '14.0.0-rc.29';

$ pnpm exec vitest run --project unit packages/lexical-y/src/__tests__/unit/YjsContract.test.ts packages/lexical-y/src/__tests__/unit/Source.test.ts
      Tests  45 passed (45)

$ pnpm run ci-check
Changeset check passed: 53 pending changeset(s) valid.
Found 0 errors   (flow; tsc, prettier, lint clean)

[vercel]

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Project	Deployment	Actions	Updated
lexical	Ready	Preview	Oct 30, 2026 9:35pm UTC
lexical-playground	Ready	Preview	Oct 30, 2026 9:35pm UTC

[meta-code-review]

AI review status for this pull request.

Review status	Updated
🟢 Reviewed (for maintainers only)	Oct 30, 2026, 9:55 PM UTC

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commit: 874806a

[meta-code-review]

This looks good to me, thanks! Annotating SUPPORTED_YJS_VERSION as string keeps its published TypeScript type stable across @y/y bumps and in line with flow/LexicalY.js.flow, the built JavaScript is unchanged, and the new assertion in YjsContract.test.ts fails exactly when the playground's @y/y pin drifts from @lexical/y's, the two-copies case the README now calls out.

Two optional, non-blocking notes:

1. Changesets warning. The Changesets job flags packages/lexical-y/src/internal/SupportedYjs.ts as published code without a changeset. SUPPORTED_YJS_VERSION first ships with #9607's pending changeset, which already announces it, so a maintainer adding the skip-changeset label fits better than a new entry (CONTRIBUTING.md, "Changesets").
2. scripts/updateVersion.mjs, lines 136-146 (nit). regenerateSupportedYjsVersion writes the module whether or not its pattern matched, so a future change to the declaration's form would turn pnpm run update-version into a silent no-op (the previous pattern does exactly that against the new annotated form), and the hint in YjsContract.test.ts would then point at a command that changes nothing. Throwing when the pattern finds no match would surface it right there. This predates the pull request, so a follow-up is fine.

[meta-code-review]

Optional (nit): .replace() returns the source unchanged when this pattern finds nothing, and the file is then written as is, so a future change to the declaration's form would make pnpm run update-version a silent no-op (the previous pattern does exactly that against the annotated form). A guard keeps it loud:

const pattern = /(export const SUPPORTED_YJS_VERSION: string = )'[^']*'/;
const source = fs.readFileSync(modulePath, 'utf8');
if (!pattern.test(source)) {
  throw new Error(
    `${SUPPORTED_YJS_MODULE}: no SUPPORTED_YJS_VERSION declaration matches ${pattern}`,
  );
}
const next = source.replace(pattern, `$1'${supported}'`);