feat(cache): probe App Page cacheability on staged Workers

[james-elicx]

Capability stack 3/9. Exact head: 16340739a0a09f558eb06946d2ac2568c2123b05. Base: #3090.

Full chain: #3108 → #3090 → #3091 → #3092 → #3103 → #3093 → #3094 → #3098 → #3113.

Summary

• add authenticated identity and completed-response cacheability probe modes for App Pages
• decide cacheability only after the response body reaches clean EOF
• bound probe capture by time and size
• expose Next.js's production-build phase during staged discovery/probing while leaving ordinary ISR requests in the production-server phase
• classify dynamic APIs, revalidation mutations, errors, redirects, incomplete responses, timeouts, oversized responses, and middleware-eligible routes as unsafe
• dynamically load probe-only runtime code only for authenticated internal requests

Safety and Next.js parity

• revalidate alone does not override dynamic runtime usage
• middleware eligibility is treated conservatively because a CDN hit in front of the Worker would skip middleware
• forged or stale capabilities cannot create a static classification
• internal capability headers are removed before user code
• production-build phase behavior follows Next.js App Router static-generation coverage

This layer covers App Pages. #3092 consumes probe results for ordinary CDN admission; #3098 extends the protocol to Pages Router.

Review guide

1. cacheability-request.ts authenticates probes and drains bounded responses.
2. cacheability-classification.ts records request-scoped route outcomes.
3. middleware-runtime.ts reports middleware participation without changing middleware behavior.
4. app-page-cache-finalizer.ts publishes the completed render outcome.
5. cacheability-probe.spec.ts exercises the built Worker under workerd.

Review size

Layer-only diff against this PR's base: 25 files, +717/-18.

Validation

• layer exact-head CI is green
• prior cumulative focused validation through feat(cache): probe Pages Router cacheability #3098 — 2,024/2,024
• current full-stack cumulative changed-file suites — 2,864/2,864
• current full-stack PPR probe/admission/Pages built-workerd E2E — 8/8
• current full-stack vp check and git diff --check

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@vinext/cloudflare@3091

npm i https://pkg.pr.new/create-vinext-app@3091

npm i https://pkg.pr.new/@vinext/types@3091

npm i https://pkg.pr.new/vinext@3091

commit: 1634073

[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

[github-actions]

Performance benchmarks

Compared 1634073 against base b3b23e7 using alternating same-runner rounds. Next.js was unchanged and skipped.

1 improved · 0 regressed · 5 within ±1.5%

Scenario	Framework	Baseline	Current	Change
Client bundle size (gzip)	vinext	142.2 KB	142.2 KB	⚫ +0.0%
Client entry size (gzip)	vinext	129.5 KB	129.5 KB	⚫ +0.0%
Dev server cold start	vinext	2.50 s	2.43 s	🟢 -2.6%
Production build time	vinext	2.70 s	2.70 s	⚫ -0.2%
RSC entry closure size (gzip)	vinext	116.7 KB	117.5 KB	⚫ +0.7%
Server bundle size (gzip)	vinext	198.2 KB	199.3 KB	⚫ +0.5%

View detailed results and traces

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