FullState

The complete current state — sent once on first contact with a peer that has never been seen before. The recipient absorbs it with us.tractat.kuilt.crdt.Quilted.piece.

upThrough is sender's own-delta high-water: the snapshot already reflects every delta sender has minted with seq <= upThrough (0 when it has minted none). The recipient fast-forwards its per-sender receive cursor past that history, drops buffered inbound deltas the snapshot covers, and acks upThrough — without this a receiver whose gap outlives the sender's GC (e.g. a late joiner) can never ack via the delta path, permanently pinning the sender's pending-delta buffer.