quiesce

Open the quiesce barrier over edge, serialized through the log: every peer that applies it marks edge locally unwritable and answers with its own final slot values (docs/heddle-ledger-relocation-design.md §6.2). Refused unless edge is RETIRED in log order.

This is the first half of reconcile, which opens the barriers it needs itself — call it directly only to fence an edge ahead of time. Idempotent, and a re-applied barrier deliberately re-runs on every peer, which is how a restarted peer re-acks.

Applied ≠ fenced: the acks arrive as their own committed acts afterwards. pendingAcks is the read that tells you whom the barrier is still waiting on.