## What changed
Move directory enumeration and candidate metadata lookups into blocking workers, batching updated-time candidate collection into one worker per scan. Check cancellation between entries and metadata lookups so dropping the async waiter stops further scanning.
Share synchronous rollout metadata resolution with the async helper, preserving plain-file precedence over compressed siblings. Retain scan limits, stable file ordering, and directory-level early stopping for creation-time listings.
## Testing
Add tests for cancellation during directory enumeration and candidate discovery in both flat and date-partitioned layouts, including plain-sibling metadata precedence and filtering of unrelated files, directories, and symlinks.
GitOrigin-RevId: 324289003b29a7d2b3220da03e3c002ab5e23eec