Type Alias: WalPhase

type WalPhase = "pending" | "authoritative" | "derived" | "complete";

WAL phase markers for tracking operation progress.

• 'pending': WAL entry written, no data changes yet
• 'authoritative': Chunk/catalog/unique writes completed
• 'derived': Filter/index updates completed (placeholder for Phase 6)
• 'complete': Operation fully done, WAL can be cleaned up