Preserve closed-route admission across cache misses

[gnoff]

Summary

The latest review follow-up (Server Action exemption and expanded fixtures) is verified locally but has not yet been pushed. The verification below distinguishes those local results from the published head.

Keep route admission independent of ISR cache contents. With Cache Components disabled, a route using dynamicParams = false and generateStaticParams() can currently return 200 for a build-generated URL, then incorrectly return 404 after revalidatePath expires its cache entry. An empty external cache causes the same failure on the first request.

For example, if the build generated /products/known, that URL remains allowed after invalidation; /products/unlisted remains disallowed regardless of cache state. If a later build removes /products/known, it must immediately stop matching, even if an external cache still holds that URL's old response.

The request handler now rejects unlisted closed URLs before looking up their ISR entries. This prevents both serving an old cache hit and generating a new response for a URL the current build does not admit. An admitted build path whose matched fallback is false regenerates using a blocking render when necessary.

The two decisions stay separate: the manifest determines whether the URL may match, while the response generator chooses how to produce an admitted response. We do not share mutable fallback-mode state between those stages.

Preserved exceptions and adapter behavior

• Server Actions: forwarding can invoke a worker at /products/[slug], not a concrete page URL. Action calls retain their existing exemption from page admission checks. A retained action must still work after the user navigates away from its closed route.
• Draft mode: an unpublished URL can be previewed without admitting it publicly or replacing its public cache entry.
• Minimal mode: the platform router remains responsible for admission before invoking the renderer.
• Adapters: rendering a routing 404 now happens outside the response cache. The previous placement could successfully send a 404 and then throw cache entry required but not generated because it returned no cache entry for a non-null cache key. The new adapter fixture reproduces this on the parent runtime.

This uses the existing prerender manifest and does not change its format or the adapter contract. The most specific matched dynamic route continues to determine the policy for open URLs, so specialized matchers can admit an open suffix without admitting an unknown closed prefix.

Regression coverage

Real fixtures cover:

• Repeated invalidation, ordinary and optional catch-all paths, time-based ISR, concurrent regeneration, and serving a stale response while regenerating in the background.
• Empty external caches and an external cache retained across two real builds. The latter verifies that the removed path's old entry still exists but is never consulted.
• Document, HEAD, navigation, prefetch, bot, rewritten, and overlapping-route requests.
• Direct and forwarded Server Actions, draft previews, and direct minimal-mode renderer invocations.
• Adapter-specific 404 handling and regeneration of admitted paths.
• The distinction between routing rejection and content that calls notFound(): an admitted URL can transition from 200 to 404 and back, including when its build render returned 404.

These legacy dynamicParams fixtures are excluded from the Cache Components matrix because that configuration does not support the API.

Stack

This is an unflagged correctness fix, placed after #98950 and before the parameter-matching API in #97393. It can land without committing to that API. The API's mixed-prefix and dynamic-tail lifecycle coverage belongs in the API layer.

Verification

• Before the original fix, the two initial regression fixtures failed 11 checks while the open-route and time-based controls passed.
• Against the parent runtime, the new adapter fixture reproduces the cache-entry invariant on document, navigation, prefetch, and bot requests, plus the invalidation regression.
• The retained Server Action regression passes on the parent runtime, fails on the published PR head, and passes with the local explicit action exemption. It also passes in development with the exemption.
• Final local production runs: all 49 tests across seven suites pass in both Webpack and fresh-native Turbopack, including the existing closed-parameter navigation suite.
• Development Turbopack request-mode coverage: 10 passed; the public-cache reuse assertion is production-only.
• Repository TypeScript, Next.js declaration generation, changed-file formatting/ESLint, and git diff --check pass.

No live deployment verification. A separate revalidate-if-generated hang with an always-empty custom cache reproduces on both this PR and its parent; its diagnostic is retained for a separate follow-up, not included or silently skipped here.

[github-actions]

Tests Passed

Commit: 78df9b6