feat(cloudflare): isolate cached response entrypoint

[james-elicx]

Part 12 of 16 in the staged CDN adapter stack. Depends on #3151.

Summary

• makes the Cloudflare CDN adapter select an uncached gateway plus a named cached-response Worker entrypoint
• keeps middleware and request-time personalization in the gateway while eligible renders use Workers Cache
• lazy-loads application rendering only on cache miss
• partitions the opaque cache URL by authority, authorization, build, invocation, and raw framework RSC selectors
• authenticates shared-response provenance through outer header composition and fails closed on reserved-header collisions
• mirrors the response entrypoint's CF-Cache-Status into X-Vinext-Cache and X-Nextjs-Cache only at final gateway egress

Validation

• 50/50 Cloudflare Worker entrypoint tests
• focused Cloudflare adapter, admission, build, and gateway-collision coverage
• fixture coverage includes App/Pages, middleware headers/cookies, draft mode, Vary, late stream failure, revalidation, HEAD, and route handlers

Review size

• Implementation: +794 / -71 LOC
• Tests and fixtures: +2058 / -111 LOC
• Other (docs, config, lockfile): +2 / -0 LOC
• 32 changed files

Measured against codex/cdn-v2-prerender-stages after rebasing onto main@a6931c0.

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@vinext/cloudflare@3152

npm i https://pkg.pr.new/create-vinext-app@3152

npm i https://pkg.pr.new/@vinext/types@3152

npm i https://pkg.pr.new/vinext@3152

commit: 792bf69

[github-actions]

Performance benchmarks

Compared 792bf69 against base 674df1d 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	142.3 KB	142.3 KB	⚫ -0.0%
Client entry size (gzip)	vinext	129.6 KB	129.6 KB	⚫ -0.0%
Dev server cold start	vinext	3.40 s	3.38 s	⚫ -0.6%
Production build time	vinext	3.50 s	3.53 s	⚫ +0.8%
RSC entry closure size (gzip)	vinext	125.6 KB	125.6 KB	⚫ -0.0%
Server bundle size (gzip)	vinext	216.4 KB	216.4 KB	⚫ -0.0%

View detailed results and traces

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

[github-actions]

Example	Preview	Production	Original
app-router-cloudflare	preview	production
pages-router-cloudflare	preview	production
app-router-playground	preview	production	original
realworld-api-rest	preview	production
nextra-docs-template	preview	production
benchmarks	preview	production
hackernews	preview	production	original
workers-cache	preview	production
static-export	preview	production
web	preview	production