cutFrontier

The causal-stability cut + frontier, recomputed on every matrix change (local apply, inbound delta, inbound QuiltMessage.Delivered, join, eviction) and published atomically as a single CutFrontier (W1 of ADR §4.6). A us.tractat.kuilt.crdt.Rga GC coordinator (#270) consumes this together with deliveredLocal and feeds them to Rga.compact(stableCut, frontierMax, delivered). For CRDTs that expose no dots (the delta-state zoo) it stays at CutFrontier.EMPTY.