fix(server): honor static freshness validators

[Boyeep]

Summary

• honor Cache-Control: no-cache instead of returning an immediate 304 for matching validators
• support If-Modified-Since at HTTP-date precision
• preserve RFC precedence: If-None-Match overrides If-Modified-Since
• keep cached and filesystem fallback static paths behaviorally identical

Stack

This is intentionally stacked on #2711 (Last-Modified and range support) and includes #2710 (weak If-None-Match comparison). Those commits will disappear from this PR's diff as the dependencies merge and the branch is rebased.

Next.js parity

Next.js static serving delegates freshness evaluation to its compiled send/fresh stack, which honors no-cache, ETag precedence, and modification dates.

Test plan

• pnpm test tests/http-conditional.test.ts tests/http-range.test.ts tests/static-file-cache.test.ts tests/serve-static.test.ts (98 passed)
• staged vp check --fix passed

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@vinext/cloudflare@2715

npm i https://pkg.pr.new/create-vinext-app@2715

npm i https://pkg.pr.new/@vinext/types@2715

npm i https://pkg.pr.new/vinext@2715

commit: 8e0cac7

[github-actions]

Performance benchmarks

Compared 8e0cac7 against base 05eee9f using alternating same-runner rounds. Next.js was unchanged and skipped.

0 improved · 1 regressed · 5 within ±1.5%

Scenario	Framework	Baseline	Current	Change
Client bundle size (gzip)	vinext	132.4 KB	132.4 KB	⚫ -0.0%
Client entry size (gzip)	vinext	119.7 KB	119.7 KB	⚫ +0.0%
Dev server cold start	vinext	2.80 s	2.89 s	🔴 +3.1%
Production build time	vinext	3.09 s	3.08 s	⚫ -0.4%
RSC entry closure size (gzip)	vinext	103.3 KB	103.3 KB	⚫ +0.0%
Server bundle size (gzip)	vinext	177.8 KB	177.8 KB	⚫ +0.0%

View detailed results and traces

_{🟢 improvement · 🔴 regression · ⚫ change below 1.5% · paired base/head}