M4 — Review gate

⚠️ HARD GATE: Do not start M4 before M2 produces a VALIDATED verdict.

M4's entire premise is that there is an autonomous merge path worth gating. That is precisely what the 2026-08-21 E2E run tests. If autonomy is falsified, M4 is REPLACED by a scope-contraction RFC — not delayed, not deferred, replaced.

Issues: #1729, #1733, #1734, #1735, #1736.