Pamela Chia 8aade77966 fix(www): gate changelog md alternate on slug set (#49754) ...

Changelog entry pages advertised a `.md` alternate tag unconditionally
while the page is ISR, so an entry published in the changelog repo
between www deploys pointed agents at a `.md` sibling that 404s until
the next build (the static file and `CHANGELOG_PAGES` are both
build-time artifacts). PR #49357 made bare-URL negotiation fail closed
for those entries; I gate the advertising side here the same way.

**Changed:**
- **No more dead `.md` links on freshly published entries**:
`getStaticProps` passes a `hasMarkdownVariant` flag computed from
`CHANGELOG_PAGES` membership and the page renders the alternate tag only
when true. An entry published between deploys carries no tag until the
build that ships its `.md` file; the set reference stays inside
`getStaticProps`, so the generated module stays out of the client
bundle.
- **Drift coverage**: `md-alternates.test.ts` gains the changelog
direction, source-level like the existing `_app.tsx` drift test; the
assertion pins the full `CHANGELOG_PAGES.has(` +
backtick-`changelog/${entry.slug}`-backtick + `)` expression so a
dropped key prefix fails the suite, and removing the gate fails it too.

**Note:** without changelog sync secrets `CHANGELOG_PAGES` is empty, so
the tag never renders in local dev. Preview and prod are the
verification surface.

## To test
Tested on Vercel preview:
- [x] Open a published changelog entry page and view source: expect
`<link rel="alternate" type="text/markdown"
href="/changelog/<slug>.md">` in the head — observed exact href
`/changelog/19669-supavisor-1-0.md`
- [x] Fetch that href: expect 200 with `content-type: text/markdown` —
observed 200, `text/markdown; charset=utf-8`
- [x] (added) Client-side nav from `/changelog` into an entry: alternate
tag appears with that entry's slug; hopping to a second entry updates
the href (no stale tag)
- [x] (added) Navigating back to `/changelog`: entry tag gone; the index
shows its own pre-existing `/changelog.md` alternate (hardcoded in
`pages/changelog.tsx`, outside this diff), and `/changelog.md` returns
200 `text/markdown`
- [x] (added) Console: zero new errors across all scenarios vs page-load
baseline

## Linear
- fixes GROWTH-1120


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Bug Fixes**
* Changelog pages now advertise a Markdown alternate link only when a
Markdown version is available.
* Prevented links to unavailable Markdown content from appearing on
changelog entries.

* **Tests**
* Added coverage to verify correct Markdown alternate detection and
rendering.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

2026-08-31 16:25:06 +08:00

..

[slug].tsx

fix(www): gate changelog md alternate on slug set (#49754)

2026-08-31 16:25:06 +08:00