B-09: ExpandBlockVolume re-reads the registry entry after acquiring
the expand inflight lock. Previously it used the entry from the
initial Lookup, which could be stale if failover changed VolumeServer
or Replicas between Lookup and PREPARE.
B-10: UpdateFullHeartbeat stale-cleanup now skips entries with
ExpandInProgress=true. Previously a primary VS restart during
coordinated expand would delete the entry (path not in heartbeat),
orphaning the volume and stranding the expand coordinator.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>