[shahednasser]

Summary

What — Upgrades all documentation apps under www/ (book, resources, api-reference, ui, user-guide, cloud) to Next.js 16.4.2, and removes the temporary --dangerouslyUseUnsupportedNextVersion flag added in #17386.

Why — @opennextjs/cloudflare now supports Next.js >=16.4.1, so we can move off 15.x and deploy to Cloudflare without the unsupported-version escape hatch.

How

• Bumped next, @next/mdx, @next/third-parties, @next/bundle-analyzer, and eslint-config-next to 16.4.2; @opennextjs/cloudflare to ^1.20.12; wrangler to ^4.151.3 (OpenNext's new peer minimum). Node engine is now >=20.9.0 (Next 16 minimum; CI already uses Node 22).
• Kept webpack (next dev/build --webpack): Turbopack is Next 16's default, but it can't take our MDX remark/rehype/recma plugins, which are JS functions with non-serializable options. OpenNext supports webpack builds.
• Added withMdxWebpackLayers in build-scripts and wrapped each app's config with it. It works around MDX export const metadata fails to build with webpack in 16.2.0 (regression from 16.1.6) vercel/next.js#91735: since 16.2, @next/mdx under webpack compiles MDX with a layer-less SWC loader, so every MDX page is treated as a client component and export const metadata fails the build. The helper routes .mdx through Next's layer-aware SWC rules instead. Remove it once the upstream issue is fixed.
• Replaced the removed next lint with eslint scoped to the same default directories (app pages components lib src) so --fix doesn't touch generated specs. Switched to plugin:@next/next/recommended-legacy, because the plugin's recommended preset is now flat-config only and breaks under FlatCompat.
• api-reference: removed a misused "use server" from MDXContent/Server. It's a component, not a Server Action, and Next 16 now rejects non-async functions in "use server" files.
• book: fixed missing commas in two highlights arrays (scheduled-jobs, extend-create-product). The typo turned [...]["6", ...] into an index lookup that yields undefined, and this crashed prerendering. Also fixed the now-validated highlight text ("link" → LINK).

Testing

• turbo run build passes for all apps and packages.
• yarn build:cloudflare (OpenNext) passes for all 6 apps.
• opennextjs-cloudflare preview for book: pages, the two fixed pages, and 404 render correctly. .md routes return 500 locally, and they do the same on the existing Next 15 build, because they fetch remote assets.
• yarn test passes (docs-ui 1366, docs-utils 36). One docs-ui run hit an existing flaky timer leak in the AiAssistant test, and it passed on rerun.
• Lint output matches develop (clean; 4 existing warnings in api-reference).

---

Checklist

• I have added a changeset for this PR — N/A, www/ packages are private
• The changes are covered by relevant tests
• I have verified the code works as intended locally

🤖 Generated with Claude Code

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[cloudflare-workers-and-pages]

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	medusa-docs-user-guide	f2eabcb	Commit Preview URL Branch Preview URL	Oct 21 2026, 12:06 PM

[cloudflare-workers-and-pages]

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✅ Deployment successful! View logs	medusa-docs-book	f2eabcb	Commit Preview URL Branch Preview URL	Oct 21 2026, 12:08 PM

[cloudflare-workers-and-pages]

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✅ Deployment successful! View logs	medusa-docs-ui	f2eabcb	Commit Preview URL Branch Preview URL	Oct 21 2026, 12:05 PM

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✅ Deployment successful! View logs	medusa-docs-resources	f2eabcb	Commit Preview URL Branch Preview URL	Oct 21 2026, 12:09 PM

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✅ Deployment successful! View logs	medusa-docs-api-reference	f2eabcb	Commit Preview URL Branch Preview URL	Oct 21 2026, 12:06 PM

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