CutFrontier

An atomically-published snapshot of the two causal-stability quantities a us.tractat.kuilt.crdt.Rga GC compactor needs (ADR-003 addendum v3, #262).

• stableCut S — elementwise min over live peers ∪ self of their delivered version vectors, maintained monotonically (a fresh joiner, which is FullState-synced, must not lower it). Drives condition 2 of the GC predicate: S.contains(I.dot) — the tombstoned op is causally stable.

• frontierMax F — max(F_live, retainedFrontier): the highest dot any peer, live or evicted-but-retained, has told us exists. Drives condition 3: delivered.dominates(F) — self has delivered everything known to exist.

The two are published together, in a single Quilter.cutFrontier emission, so a compactor can never observe an intermediate state in which F has floored below a known-to-exist dot — wiring invariant W1 of ADR §4.6. A consumer must read the whole CutFrontier, not re-derive the halves from separate sources.