FailoverDiagnostic now carries V2PromotionEnabled and V2PromotionReady
fields. MasterServer.FailoverDiagnosticSnapshot() enriches the failover
state diagnostic with rollout gate visibility so operators can confirm
whether the master is on V1, V2, or V2-fail-closed-placeholder mode.
Update phase-20.md: document default=false rollout policy (safe default
until proto regen enables evidence RPC, then flip to default true).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
2b97cd04b8