- Shallow listing: read per-directory _index.json once for eTags instead
of N serial .meta.json reads. Validate prefix for path traversal and
verify normalized target stays within bucket root.
- Recursive listing: cache full per-directory index during the walk so
each _index.json is parsed at most once per call.
- Per-bucket listing cache with 5s TTL and per-bucket rebuild mutex.
Invalidated on put/delete/copy/metadata/tags/multipart-complete.
Pagination uses partition_point for O(log n) start lookup.
- UI stream endpoint now actually streams via mpsc + Body::from_stream
instead of buffering into a Vec<String>. Cancels producer on client
disconnect.
- UI JSON endpoint honors delimiter=/ and returns common_prefixes.
- run_blocking wrapper dispatches sync filesystem work via
block_in_place on multi-threaded runtimes, falls back to inline on
current-thread runtimes (unit tests).
