Vendoring the fonts dropped the 8 font preload links (#730 follow-up)

[TortoiseWolfe]

Vendoring the fonts (#730) removed the build's dependency on Google, and cost one thing worth
recording: next/font used to emit <link rel="preload" as="font" crossorigin> for the eight
preloadable latin faces. Production now emits zero — verified against the live site.

Impact, stated honestly

Small, and not a correctness bug:

• The faces still load. Verified on prod: 70 @font-face blocks, 34 woff2, and a real file
  serving HTTP 200 · 24,900 bytes · font/woff2.
• font-display: swap still applies, and the six size-adjust/ascent-override fallback
  faces survived vendoring — so text renders immediately in a metric-matched fallback and
  there is no layout shift.

What is lost is discovery time. With a preload the browser starts fetching the face from the
HTML; without one it must parse the CSS and reach layout first. That is a slightly longer FOUT
on a cold cache, most visible on a slow connection.

Why it is not a one-line fix

The filenames are content-hashed by the bundler — on prod they carry a second hash,
0c310187b552b27d-s.0c310187.woff2 — so a preload link cannot be hardcoded in layout.tsx.
Options, roughly in order of how much they touch:

1. Import the font files in TS so the bundler resolves the URLs, then render the eight
   <link rel="preload"> tags from those values. Keeps a single source of truth. The .p
   suffix already marks which faces next/font considered preloadable, so the set is known.
2. Emit the tags from the vendoring script into a generated TS module that layout.tsx
   imports — same idea, but the hash is only correct if the script runs after every build that
   changes a font, which is fragile.
3. Accept it. With swap plus metric-matched fallbacks the visible cost is small, and the
   build no longer depends on a third party. This is a defensible trade — it just should be a
   decision rather than an oversight.

Do not

Re-introduce next/font/google to get the preloads back. That restores the build-time
dependency on fonts.gstatic.com that broke a production deploy and a CI shard inside twelve
hours, which is a strictly worse failure than a marginally later font fetch.
tests/unit/fonts-vendored.test.ts will fail if anyone tries.

Related

• Production deploys can fail because Google Fonts is unreachable from the runner #730 — the vendoring, and why the dependency had to go.
• Visual refresh foundation: theme-aware depth tokens, Archivo/JetBrains type via next/font, and an icon system (blocks the rest of the epic) #377 — the four-layer font stack; any change here has to respect that the --font-*
  variables live on :root.