fix(app-router): align navigation prefetch commits

[NathanDrake2406]

Summary

This ports the relevant behaviour from Next.js's test/e2e/app-dir/navigation/navigation.test.ts and fixes the App Router navigation lifecycle issues that surfaced in the deploy harness:

• keep optimistic/loading-shell prefetch payloads out of final navigation consumption, even if a later Link prefetch attempts to promote the cache entry
• omit destination metadata from loading-shell prefetch payloads so a prefetched loading boundary cannot update the document title before the real navigation content commits
• render the final authoritative payload against the latest router state after the optimistic shell has mounted, avoiding stale-state no-ops
• resolve same-path search+hash navigations when the visible tree is unchanged, so URL and hash-scroll side effects still complete
• route App-to-Pages/document navigations through the App Router's MPA scheduler before falling back to a hard browser navigation

Upstream references

• Next.js navigation E2E hash contract: https://github.com/vercel/next.js/blob/ee6e79b1792a4d401ddf2480f40a83549fe8e722/test/e2e/app-dir/navigation/navigation.test.ts#L142-L195
• Next.js async metadata navigation contract: https://github.com/vercel/next.js/blob/ee6e79b1792a4d401ddf2480f40a83549fe8e722/test/e2e/app-dir/navigation/navigation.test.ts#L738-L770
• Next.js PrefetchKind.AUTO / FULL semantics: https://github.com/vercel/next.js/blob/ee6e79b1792a4d401ddf2480f40a83549fe8e722/packages/next/src/client/components/router-reducer/router-reducer-types.ts#L131-L146
• Next.js loading-boundary prefetch pruning: https://github.com/vercel/next.js/blob/ee6e79b1792a4d401ddf2480f40a83549fe8e722/packages/next/src/server/app-render/walk-tree-with-flight-router-state.tsx#L107-L134
• Next.js segment prefetch scheduler: https://github.com/vercel/next.js/blob/ee6e79b1792a4d401ddf2480f40a83549fe8e722/packages/next/src/client/components/segment-cache/scheduler.ts
• Next.js route cache implementation: https://github.com/vercel/next.js/blob/ee6e79b1792a4d401ddf2480f40a83549fe8e722/packages/next/src/client/components/segment-cache/cache.ts
• Next.js Link prefetch/navigation entrypoint: https://github.com/vercel/next.js/blob/ee6e79b1792a4d401ddf2480f40a83549fe8e722/packages/next/src/client/link.tsx

Test notes

The local Playwright port keeps the same observable contracts as the upstream file. The hash fixture uses the same link structure and RSC-request assertions; target scroll positions are computed from the rendered fixture because app-basic has a different root/template offset than Next.js's upstream fixture. The async metadata fixture preserves the 5s metadata delay and fallback/content/title assertions. The upstream deploy-suite run remains the exact file-scope parity check.

Verification

• vp test run tests/app-browser-entry.test.ts -t "same-path search and hash|stays pending until NavigationCommitSignal|authoritative payload"
• PLAYWRIGHT_PROJECT=app-router pnpm exec playwright test tests/e2e/app-router/nextjs-compat/navigation.spec.ts --grep "hash|navigating to a page with async metadata"
• vp test run tests/app-page-route-wiring.test.ts tests/prefetch-cache.test.ts tests/app-browser-entry.test.ts tests/link-navigation.test.ts tests/link.test.ts tests/navigation-planner-prefetch-reuse.test.ts
• vp check
• vp env exec --node 24 ./scripts/run-nextjs-deploy-suite.sh /Users/nathan/Projects/vinext/.refs/nextjs-v16.2.6 --retries 0 -c 1 --debug test/e2e/app-dir/navigation/navigation.test.ts

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@vinext/cloudflare@2104

npm i https://pkg.pr.new/vinext@2104

commit: c4d132e