43-site classification (8 category-A barrier-gated, 6 category-B
receipt-ACK, ~29 category-C) recorded in tasks.md. Reviewer-confirmed
exhaustive from the producer side and the opcode dispatch: every
WAIT-class WAL producer reaches its requester reply only through a
commit barrier; no handler bypasses wal_classify. Zero production
changes. Noted: WORKER_UPDATE has a reply-less second producer
(mark_worker_back liveness sweep) — not a violation, future RETAIN
refinement candidate.