A refs/wip snapshot ref is deleted only when both hold: its commit's tree is
already reachable from main, and it is older than 24h. Reachability is the safety
floor — a snapshot exists because the work was committed nowhere else, so an
unreachable one is the last copy and is never swept. Every deletion logs the ref
and the sha.
/members gains wipRefs{count,costBytes} so the growth is visible.
Verified against real git, not only the fakes: a recoverable+old ref is deleted,
a recoverable+young one survives the age floor, and the last copy survives. A repo
with no main deletes nothing, and a repo with no snapshots is a clean no-op.
Closes#67
Dai Ha
15ff6bcde5