Stalled RSC Request Permanently Kills Soft Navigation With StaleTimes.Dynamic > 0

The segment cache stores an unsettled promise from a stalled RSC request in the BFCache. When staleTimes.dynamic > 0, the cache serves this poisoned entry with needsDynamicRequest=false, suppressing network requests. Later, React suspends on the never-resolving prefetchRsc promise and the navigation error is silently swallowed by navigateToUnknownRoute().catch(() => state), so the route becomes permanently dead until a full reload.

1. npm install && npm run build && npm start with config experimental.staleTimes={dynamic:60, static:300}. 2. Open localhost:3000 and click 'Run reproduction'. The harness shims fetch to hang RSC requests for /target, clicks the link to poison the cache, restores fetch, then repeatedly clicks and logs URL changes and request counts. 3. Observe that post-restore clicks are dead: URL unchanged, zero requests until staleAt expires, then one request but still dead. Compare with dynamic unset: requests are issued but navigation still fails. Control link /other works normally.

This fix may change cache behavior by delaying or skipping caching of in-flight entries, potentially increasing server requests. The promise settlement detection must be race-free; concurrent navigations to the same route could lead to multiple cached entries if not synchronized. The full navigation fallback should be limited to avoid redirect loops and must respect client-side routing preferences. Rollback is safe by reverting both changes, but testing under slow network and concurrent navigation scenarios is advised.