The salvaged commit only swept `hermes-sync-back-*.tar`. The extraction
staging dir (`tempfile.TemporaryDirectory(prefix="hermes-sync-back-")`) is
leaked by the same hard kill, so the sweep now reclaims both shapes and
returns the count. The window drops from 24 h to 6 h (the reporter's
value): archives appear every few minutes on a busy gateway and a live
transfer is never hours old. Tests trimmed to two invariants: the sweep
touches only stale prefixed entries, and a real sync_back reclaims a
leaked archive while writing its own tar under the identifiable prefix.
bae9f8ab85