Per internal#562 audit, HTML pages on docs.moleculesai.app respond with
`Cache-Control: max-age=0, must-revalidate` while Vercel Edge is HITting them.
That means a browser round-trip to the edge on every navigation just to get a
304 — no benefit from edge cache being warm.
Adds a single `headers()` rule in next.config.mjs that sets
`public, max-age=0, s-maxage=300, stale-while-revalidate=86400` on every path
EXCEPT Next.js internals (/_next/static and /_next/image — already immutable
and uncacheable-override per Next.js docs) and /api/* (app-controlled cache).
The source pattern `/((?!_next/static|_next/image|api/).*)` uses path-to-regexp
negative lookahead — same pattern Next.js's own proxy.js doc recommends for
negative matching.
This site has no /public/ dir so there are no unhashed brand assets to
configure separately — those will inherit the same HTML cache rule, which is
the right default for our content (changelog/docs MDX, not high-churn).
Expected impact: edge-HIT ratio on HTML pages rises from ~0% to >90% during
typical nav bursts (5 min freshness) and 99%+ for repeat visits within 24 h
(stale-while-revalidate window). Hashed _next/static assets retain their
`immutable, max-age=31536000` headers — Next.js sets these and they cannot
be overridden in next.config.
RFC: internal#562 (step 1 — Vercel side; CF cache rules tracked separately)
documentation-specialist