feat(registry): add next-intl localized routes

[bntvllnt]

Summary

• Add next-intl routing for English and French registry app pages, with localized metadata, hreflang alternates, sitemap entries, and locale-aware navigation/chrome.
• Move MDX page content to content/pages/<slug>/<locale>.mdx, add French pages, and add a CI translation check for required default-locale MDX.
• Keep machine endpoints canonical while adding localized llms routes and /r/<name>.<locale>.json description overlays.
• Remediate the i18n/SEO blocker for comparison routes: /fr/vs and /fr/vs/shadcn now have French metadata and visible French body/table copy, so the advertised French canonical, sitemap, and hreflang alternates no longer point at English-only comparison pages.
• Reconciled the branch with current origin/main after PR fix(registry): upgrade Next.js to 16.2.6 #357 by preserving the PR's localized-route changes and main's Next.js / @next/mdx 16.2.6 update in apps/registry/package.json and pnpm-lock.yaml.

Dependency tradeoff

• Adds next-intl to the registry app only. This brings next-intl, use-intl, and @formatjs/* runtime packages, but avoids a bespoke i18n router/message loader and matches the issue request.

Validation

Earlier not-found fix validation on fb51552cf235dd918bc90baf58fb8bda1add1a61 before the 2026-05-31 branch refresh:

• PASS: tsc --noEmit --project tsconfig.json (0 errors)
• PASS: targeted ESLint for app/[locale]/not-found.tsx, app/[locale]/llms.txt/route.ts, app/[locale]/llms-full.txt/route.ts
• FIX: not-found.tsx converted from sync client component to async server component; useLocale/useTranslations replaced with getLocale/getTranslations from next-intl/server — resolves metadata + client-hook conflict that caused Next.js build error
• FIX: functional/no-loop-statements eslint-disable removed from both llms route files; loops replaced with map+spread (llms.txt) and reduce (llms-full.txt)

Earlier reconciliation validation on fb51552cf235dd918bc90baf58fb8bda1add1a61 before the 2026-05-31 branch refresh:

• PASS: git diff --check
• PASS: pnpm -F @vllnt/ui-registry check:translations
• PASS: pnpm -F @vllnt/ui-registry exec tsc --noEmit --project tsconfig.json
• PASS: pnpm -F @vllnt/ui-registry registry:build

Latest remediation validation on earlier head d66a08c69581cfc3ff69cd0213461890be0c4bc9:

• PASS: pnpm -F @vllnt/ui-registry exec tsc --noEmit --project tsconfig.json
• PASS: targeted ESLint for edited comparison route files: pnpm -F @vllnt/ui-registry exec eslint 'app/[locale]/vs/page.tsx' 'app/[locale]/vs/shadcn/page.tsx'
• PASS: git diff --check
• FAIL baseline/unrelated: pnpm -F @vllnt/ui-registry lint exited 1 with 221 existing errors outside the edited comparison files, including app/manifest.ts, app/mcp/route.ts, app/robots.ts, lib/jsonld.ts, registry scripts, and types/registry.ts.

Prior branch validation retained from earlier HEAD:

• pnpm install --frozen-lockfile
• pnpm -F @vllnt/ui lint
• pnpm -F @vllnt/ui exec tsc --noEmit --project tsconfig.build.json
• pnpm -F @vllnt/ui-registry exec tsc --noEmit --project tsconfig.json
• pnpm build
• pnpm test:once
• pnpm -F @vllnt/ui-registry check:translations
• pnpm -F @vllnt/ui check:use-client
• pnpm -F @vllnt/ui exec tsx scripts/check-story-coverage.ts
• pnpm -F @vllnt/ui exec tsx scripts/verify-stories.ts
• pnpm -F @vllnt/ui build-storybook
• git diff --check
• Targeted registry ESLint over touched runtime route/component/lib files, including localized routes and llms routes.

Runtime smoke

After the earlier pnpm build, ran pnpm -F @vllnt/ui-registry exec next start -p 3011 and verified:

• curl -I http://localhost:3011/en/llms.txt -> 308 to http://localhost:3011/llms.txt
• curl -I http://localhost:3011/en/llms-full.txt -> 308 to http://localhost:3011/llms-full.txt
• curl -I http://localhost:3011/request-component -> 200 with rewrite to /en/request-component and NEXT_LOCALE=en
• curl http://localhost:3011/r/button.fr.json -> localized overlay JSON with locale: "fr", sourceLocale: "en", and canonical /r/button.json
• curl http://localhost:3011/fr/llms.txt | head -8 -> French llms header/content

Branch freshness

• Refreshed against main on 2026-05-31T15:06:18Z.
• Current head: 83f8e60390854a137f65d3af7ca7738bda6be47c.
• Current base: 7d14e563f349259d071634e02a8f489fedb6b0bd.
• Merge state at refresh: UNSTABLE.
• Checks at refresh: RERUNNING (2 active/non-terminal check(s); 0 completed non-green check(s) currently visible).
• This section supersedes older current-head or CI-status notes above.

Closes #281

[bntvllnt]

@bntvllnt Review verdict: APPROVE recommended for reviewer triage — no source blockers found

Head reviewed: 053e00a11db6b02a688a887b3cf27b41be84bd71

No code blockers found after full changed-file review of the localized registry route/content implementation.

Evidence checked:

• PR body references Closes #281 and names the current head.
• CI includes pnpm -F @vllnt/ui-registry check:translations; local check:translations passed and en/fr message key parity is clean.
• Locale routing, canonical/hreflang helpers, localized sitemap entries, machine route redirects, and localized overlay registry handling are internally consistent in the changed files.

STATUS

• GitHub Actions/code checks are green and Vercel – storybook is SUCCESS.
• Vercel – ui.vllnt.ai: FAILURE is eligible for the PM stale-Vercel reviewer-triage waiver only; it is not merge/release approval.
• Validation gap: local registry TypeScript could not be reproduced because this local workspace lacks next-intl in node_modules; live GitHub Quality Gates are green.

[vllnt-pilot]

Preview ready · Updated 2026-06-03T20:04:55Z

Service	Status	Preview
storybook	Ready	https://pr-350-storybook.preview.vllnt.ai

Inspect

• Tailnet-only by default (not reachable from public internet)
• Cert: real Let's Encrypt wildcard
• Reply with /clean to destroy this preview now

[bntvllnt]

Review — 1 blocking finding

BLOCKING

• C1 — French 404 still ships English metadata and CTA copy
  • Evidence: apps/registry/app/[locale]/not-found.tsx:8-11 exports static English metadata (Page not found, We couldn't find...) for every locale, and apps/registry/app/[locale]/not-found.tsx:52-65 hardcodes Read the docs / Request a component instead of using the existing common.readDocs / common.requestComponent messages.
  • Why it matters: this PR's core contract is localized registry routes. On /fr/... misses, the page body partly uses French via getTranslations, but the route still renders English CTA text and English document metadata while the layout declares html lang="fr". That leaves the French localized surface visibly incomplete and contradicts the PR's stated localization remediation.
  • Fix: replace the hardcoded CTA labels with translated messages and move the 404 metadata behind locale-aware generateMetadata/translation lookup (or otherwise return locale-specific metadata for [locale]).

WARN

• None beyond the blocker above.

VERIFIED CLEAN

• Re-fetched the live PR before publication: PR #350 is open/non-draft at fb51552cf235dd918bc90baf58fb8bda1add1a61, base main, merge state CLEAN.
• Confirmed current checks are green for issue-link, Quality Gates, CodeQL, react-doctor, registry/storybook build/deploy, and preview deploy.
• Reviewed the localized App Router migration, i18n request/routing/proxy setup, machine-readable llms routes, /r/[name] locale response behavior, sitemap/SEO helpers, content/sidebar loaders, translation messages, registry metadata/scripts, CI/package/lockfile changes, and generated registry artifacts. No additional blocking issue was found in those areas.
• PR body includes Closes #281 and references the current head SHA.

VALIDATION

• Ran/read: gh pr view 350 --repo vllnt/ui --json ... and gh pr checks 350 --repo vllnt/ui --json name,state,bucket,link,workflow.
• Inspected diff artifacts from detached worktree /home/ubuntu/ui/.worktrees/pr-350-review-t43617508 at fb51552cf235dd918bc90baf58fb8bda1add1a61 against origin/main.
• Attempted local pnpm -F @vllnt/ui-registry check:translations; it could not run in the detached worktree because local node_modules/tsx are missing (spawn ENOENT). I did not treat that environment failure as PR code evidence.

Note: authenticated reviewer appears to be the PR author, so this is a blocking COMMENT review rather than an autonomous approval or merge.

[bntvllnt]

Closing in favor of a fresh next-intl implementation on current main. This branch localizes 6 page groups under [locale]/ but predates main's newer pages (/templates, /design, /releases, /changelog) and relies on as-needed locale prefixing without middleware — merging as-is would leave a half-localized, route-inconsistent app. Re-implementing i18n cleanly on current main (covering all current pages, with middleware), reusing this branch's locale config, message catalogs, and translated MDX. Issue #281 stays open.