fix(build): skip unhelpful precompressed variants

[Boyeep]

What changed

• emit Brotli, gzip, and zstd variants independently only when smaller than identity
• remove obsolete variants when content becomes incompressible or falls below the threshold
• replace compressed files atomically
• make the startup static cache reject oversized encoded variants as defense in depth

Why

Precompression previously wrote every encoding result regardless of size. High-entropy assets could therefore produce representations larger than the original, which the production server would still prefer during content negotiation. Reruns could also retain variants that were no longer useful.

Impact

Precompressed assets cannot increase transferred bytes, stale variants are cleaned up, and partially written variants are not exposed to the production server.

Validation

• vp test run tests/precompress.test.ts tests/static-file-cache.test.ts
• vp check packages/vinext/src/build/precompress.ts packages/vinext/src/server/static-file-cache.ts tests/precompress.test.ts tests/static-file-cache.test.ts

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@vinext/cloudflare@2712

npm i https://pkg.pr.new/create-vinext-app@2712

npm i https://pkg.pr.new/@vinext/types@2712

npm i https://pkg.pr.new/vinext@2712

commit: b1ebedd

[github-actions]

Performance benchmarks

Compared b1ebedd against base 05eee9f using alternating same-runner rounds. Next.js was unchanged and skipped.

0 improved · 0 regressed · 6 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	2.79 s	2.81 s	⚫ +0.7%
Production build time	vinext	2.95 s	2.93 s	⚫ -0.7%
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}