fix(swingset): point the StyleX PostCSS plugin at the Mosaic source

[alexcarpenter]

Description

Since #9765 extracted Mosaic into @clerk/mosaic, production builds of Swingset render every Mosaic component unstyled (the Vercel previews show bare text). next dev is unaffected because the unplugin's runtimeInjection injects atoms and token defaults at runtime.

Swingset's @stylexjs/postcss-plugin was relying on auto-discovery to find the Mosaic source: it scans any direct dependency whose manifest lists @stylexjs/stylex under dependencies, peerDependencies, or optionalDependencies. @clerk/ui did, so packages/ui/src (Mosaic included) was scanned. @clerk/mosaic keeps StyleX in devDependencies, since tsdown inlines it into the published bundle, so the plugin skipped the package, scanned nothing, and replaced @stylex; with an empty sheet.

This gives the plugin an explicit include covering Swingset's own stories and packages/mosaic/src, so extraction no longer depends on how @clerk/mosaic declares its dependencies.

Checklist

• pnpm test runs as expected.
• pnpm build runs as expected.
• (If applicable) JSDoc comments have been added or updated for any package exports
• (If applicable) Documentation has been updated

Type of change

• 🐛 Bug fix
• 🌟 New feature
• 🔨 Breaking change
• 📖 Refactoring / dependency upgrade / documentation
• other:

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated
clerk-js-sandbox	Ready	Preview	Sep 17, 2026 4:02pm UTC
swingset	Ready	Preview	Sep 17, 2026 4:02pm UTC

[changeset-bot]

🦋 Changeset detected

Latest commit: 1767ddf

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 0 packages

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository YAML (base), Organization UI (inherited)

Review profile: ASSERTIVE

Plan: Team

Run ID: 5ac40ade-5a21-4a81-9d53-c2188bbc0824

📥 Commits

Reviewing files that changed from the base of the PR and between 970583c and 1767ddf.

📒 Files selected for processing (2)

• .changeset/swingset-stylex-include.md
• packages/swingset/postcss.config.mjs

🔗 Linked repositories identified

CodeRabbit considers these linked repositories for cross-repo context during reviews:

• clerk/clerk_go (manual)
• clerk/dashboard (manual)
• clerk/accounts (manual)
• clerk/backoffice (manual)
• clerk/clerk (manual)
• clerk/clerk-docs (manual)
• clerk/cloudflare-workers (manual)
• clerk/cli (auto-detected)
• clerk/clerk-ios (auto-detected)
• clerk/clerk-android (auto-detected)

Included review availability: 1 review is currently available. Your included PR review attempts over the past 7 days set your current allowance at 4 reviews per hour.

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📝 Walkthrough

Walkthrough

The Swingset PostCSS configuration now includes TypeScript and TSX sources from both the local src directory and the Mosaic package’s src directory for StyleX processing. An empty Changesets metadata file was added.

Priority: ➖ Normal

Estimated code review effort: 1 (Trivial) | ~5 minutes

Merge Risk: ⚪ Minimal · up to 1767d

The configuration covers the executable Swingset story sources; the MDX files contain documentation examples rather than omitted runtime styles. The change is ready to merge.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 1…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly identifies the fix to the Swingset StyleX PostCSS configuration and the Mosaic source path.
Description check	✅ Passed	The description explains the production styling bug, its cause, and the explicit source inclusion fix.

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commit: 1767ddf