Add a dedicated cleanup path for incomplete snapshots instead of letting
retention prune them implicitly. The retention plan now exposes a guarded
form that requires host and delete-count confirmation before removing
.incomplete snapshot directories and their SQL records.
Keep scheduled/manual retention behavior unchanged, add path safety checks,
and cover cleanup success, confirmation failures, max-delete limits, and
unexpected paths in tests.
Refs #10
Peter van Arkel
d0c23deb72