diff --git a/sw-block/.private/phase/phase-20.md b/sw-block/.private/phase/phase-20.md
index dedb5ffe1..b05e92942 100644
--- a/sw-block/.private/phase/phase-20.md
+++ b/sw-block/.private/phase/phase-20.md
@@ -207,9 +207,11 @@ authorization.
   6. Bump epoch, enqueue assignment to selected candidate
 
 **Legacy fallback policy**:
-- Add `--block.v2-promotion` flag (default `true`)
+- Add `--block.v2Promotion` flag (default `false` — safe rollout default
+  until proto regen enables the evidence RPC; once RPC is live, flip to
+  default `true`)
 - When `true`: `promoteReplicaV2()` with fail-closed on evidence failure
-- When `false`: existing `promoteReplica()` (V1 path)
+- When `false`: existing `promoteReplicaV1()` (V1 path)
 - The flag is observable via `/vol/status` and metrics
 - The flag is intended to be removed once V2 is validated, not permanent
 
diff --git a/weed/server/master_block_failover.go b/weed/server/master_block_failover.go
index 9c7b7120b..ada422c79 100644
--- a/weed/server/master_block_failover.go
+++ b/weed/server/master_block_failover.go
@@ -54,6 +54,8 @@ type FailoverVolumeState struct {
 // Volume-oriented: each entry describes one volume's failover state.
 // Aggregate counts are derived from the volume list.
 type FailoverDiagnostic struct {
+	V2PromotionEnabled   bool           // T3: whether durability-first V2 promotion is active
+	V2PromotionReady     bool           // T3: whether V2 evidence querier is wired (false = fail-closed placeholder)
 	Volumes              []FailoverVolumeState
 	PendingRebuildCount  map[string]int // dead server → count of pending rebuilds
 	DeferredPromotionCount map[string]int // dead server → count of deferred promotion timers
@@ -93,6 +95,15 @@ func (fs *blockFailoverState) DiagnosticSnapshot() FailoverDiagnostic {
 	return diag
 }
 
+// FailoverDiagnosticSnapshot returns a FailoverDiagnostic enriched with
+// V2 promotion rollout state so operators can observe the active mode.
+func (ms *MasterServer) FailoverDiagnosticSnapshot() FailoverDiagnostic {
+	diag := ms.blockFailover.DiagnosticSnapshot()
+	diag.V2PromotionEnabled = ms.blockV2Promotion
+	diag.V2PromotionReady = ms.blockV2Promotion && ms.blockVSQueryEvidence != nil
+	return diag
+}
+
 // PublicationDiagnostic is a bounded read-only snapshot comparing the
 // operator-visible publication (LookupBlockVolume response) against the
 // registry authority for one volume. P3 diagnosability surface for S2.