SyncScopeMove

const SyncScopeMove: Model<SyncScopeMoveDocument>

C4: durable marker written in the same op-scope as a scope move, replacing the racy _syncPrevStream post-image read. The old stream tombstones the document from this marker (change-stream fan-out + snapshot catch-up), so a racing second write that overwrites _syncPrevStream can no longer erase the tombstone.

Retention: reaped only by compactTombstones, which honors the owning model's retentionDays and records a compactedThroughSeq watermark as it deletes.