fix(react-router): skip manifest patch caching on aborted route discovery

[kdelay]

fetchAndApplyManifestPatches mutates manifest.routes and adds the requested paths to the module-level discoveredPaths cache as soon as the manifest response settles, but the patch callback the router hands to patchRoutesOnNavigation no-ops once the triggering navigation/fetcher signal has aborted (router.ts).

If an abort lands in the window between the manifest JSON settling and the patches being applied, the paths end up cached as discovered while the client route tree was never patched. Every later navigation to those paths early-returns at the discoveredPaths check, so discovery never runs again for the rest of the session — a splat route can match instead and its server loader runs, or a later child patch fails with No route found to patch children into. Only a hard reload clears it, since the cache is module state.

This bails out before either mutation when the signal has aborted, so an aborted discovery leaves no trace and the next navigation to that path discovers it normally. The eager prefetch path in useFogOFWarDiscovery passes no signal, so it is unaffected.

Closes #15327

Tests

packages/react-router/__tests__/dom/ssr/fog-of-war-test.ts now drives getPatchRoutesOnNavigationFunction with a mocked fetch (as lazy-discovery-test.ts does) and a patch that mirrors the router's abort no-op:

• a discovery aborted while the manifest is being read is re-attempted and patched on the next navigation to the same path — this failed before the change, because the second attempt never re-fetched
• a discovery that is not aborted still patches once and is not fetched again

[github-actions]

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[github-actions]

✅ Change File Found

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Type	Change
patch	Don't cache a lazily-discovered path when the navigation/fetcher that triggered discovery aborts mid-flight