next.js

ac55fd99 - Fix duplicate background revalidation for `'use cache'` (#98446)

Fix duplicate background revalidation for `'use cache'` (#98446) An early `cacheHandler.set()` call previously made subsequent same-key `get()` calls wait for generation and persistence. This prevented another background revalidation, but those requests waited instead of receiving the existing stale data. The work in #94694 added private-cache persistence in dev. Its helper refactor made cross-request invocations wait for cache writes before retrying root-param-specific lookups. It also moved the coarse-key `set()` call after entry collection. That unintentionally allowed subsequent requests to receive stale data and start another background revalidation while one was already running. This change tracks background work separately for each lookup key within a runtime instance. Subsequent requests can receive the existing stale entry without waiting for generation or starting duplicate work. The task remains registered until collection and its cache writes settle. Each lookup records existing work before calling `get()`, so a slow lookup does not start another revalidation after the task it observed has completed. The handler still receives `set()` after collection, including asynchronous rendering of the cached result. Subsequent `get()` calls can still block while the handler persists the entry. We accept that remaining wait to preserve the cache-handler contract without bypassing handler reads. **Alternatives Considered** - Restore early `set()` calls and rely on the handler's pending-set promises. This would prevent duplicate regeneration, but would also make subsequent requests wait for generation again instead of receiving stale data. - Extend the existing cross-request sharing mechanism through background revalidation. We prototyped retaining stale and regenerated results, but that required additional stream ownership, invalidation checks, and root-param matching. The separate background-task map avoids those changes and leaves cold and foreground generation unchanged. Fixes #98326