Concurrent WriteLBA/Trim calls could deliver WAL entries to replicas
out of LSN order: two goroutines allocate LSN 4 and 5 concurrently,
but LSN 5 could reach the replica first via ShipAll, causing the
replica to reject it as an LSN gap.
shipMu now wraps nextLSN.Add + wal.Append + ShipAll in both
WriteLBA and Trim, guaranteeing LSN-ordered delivery to replicas
under concurrent writers.
The dirty map update and WAL pressure check happen after shipMu
is released — they don't need ordering guarantees.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
