[pull] canary from vercel:canary - #1413

## Summary

- Distinguish an unreachable agent-feedback rollout gate from an
explicitly disabled rollout.
- Exit the internal feedback-instructions command with actionable retry
guidance so sandboxed agents can request network access instead of
silently skipping reports.

## Verification

- `pnpm exec jest
packages/next/src/cli/internal/agent-feedback-status.test.ts
packages/next/src/cli/internal/agent-feedback-instructions.test.ts
--runInBand`
- `pnpm --filter=next types`
- `pnpm --filter=next build`
- Verified the built CLI exits 1 with retry guidance without network
access and returns the protocol with network access.

<!-- NEXT_JS_LLM -->

## Summary

This enables strict route matching by default. App Router URLs that
cannot construct a complete route tree are rejected, unreachable pages
are reported, and incomplete catch-all matchers are pruned.

If strict route matching finds one of these invalid route structures,
Next.js warns that the validation implies a bug in the app and points to
`deprecated.looseRouteMatching: true` as a temporary escape hatch. The
deprecated option only accepts `true`; strict matching remains the
normalized internal behavior when the option is absent.

For example, this layout cannot render either URL as a complete route
because neither named slot has a page or default for the URL matched by
its sibling:

```text
app/
├── layout.tsx
├── @left/foo/page.tsx
└── @right/bar/page.tsx
```

Previously the app could depend on soft navigation preserving stale slot
state even though `/foo` and `/bar` could not be loaded directly. With
strict route matching enabled, the build reports the incompatible slots
and the two unreachable pages. Adding explicit defaults makes the
intended fallback behavior valid again.

## Verification

- `pnpm build-all`
- `pnpm exec jest packages/next/src/server/config.test.ts --runInBand`
- `parallel-routes-pruned-matchers` in production with Turbopack and
Webpack
- `parallel-routes-leaf-segments` in production with Turbopack
- strict diagnostic fixtures in production with Turbopack

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## Summary

- Narrow build-time generator names to a literal type that can be
extended as new generators are added.
- Split the combined revalidation diagnostic into render,
cached-function, and build-time-generator errors so each failure reports
only its actual context and never needs a fallback generator name.
- Cover all three contexts in the existing development and production
test suites.

Follow-up to the review feedback on #98891.

## Verification

- `HEADLESS=true pnpm test-dev-webpack
test/e2e/app-dir/revalidatetag-rsc/revalidatetag-rsc.test.ts` (3 tests)
- `HEADLESS=true pnpm test-start-webpack
test/e2e/app-dir/revalidatetag-rsc/revalidatetag-rsc.test.ts` (3 tests)
- Production Webpack `generate-static-params-errors` suite (6 tests)
- `pnpm --filter=next types`

<!-- NEXT_JS_LLM -->

## Summary

Migrate the shared cache-components error tests and two additional
legacy deployment exclusions from `skipDeployment`/`skipped` to test
gates, so these callers can land on canary before the API is removed.

Place the cache-error gate on the existing named `describe` boundary in
each of the 12 `.test.ts` entry files. Jest transforms gate pragmas in
test files; a gate in the shared utility would be inert. The helper
continues registering the same tests inside those entry-level suites,
preserving their names and snapshots. These tests inspect local
prerender builds and cannot run against a deployment.

The other two callers cover segment-cache fixture mutation and
production output-file tracing. This is a standalone preparatory
migration, not the removal of the legacy API itself.

## Verification

- Rebased onto canary at `ccef3db535`; the stable patch ID matches the
original migration exactly.
- On the rebased tree, all 77 gate infrastructure unit tests passed.
- Deploy-mode Jest collection of all 12 cache-error entry files: 236
skipped, zero executed, and no deployment started.
- Prettier, ESLint, and diff whitespace checks passed.
- Full bootstrap attempted but blocked by missing package-level
dependencies (`microbundle`) in the temporary worktree; no full
dev/start integration run is claimed.

<!-- NEXT_JS_LLM -->