diff --git a/weed/server/block_rebuild_remote.go b/weed/server/block_rebuild_remote.go
index db5e80541..5792634eb 100644
--- a/weed/server/block_rebuild_remote.go
+++ b/weed/server/block_rebuild_remote.go
@@ -144,10 +144,15 @@ func (r *RemoteRebuildIO) TransferFullBase(committedLSN uint64) (uint64, error)
 			return achieved, nil
 
 		case blockvol.SessionAckFailed:
-			// Forward the ack for observation cleanup (pins, watchdog, engine
-			// SessionFailed). Then return the sentinel error so ExecutePendingRebuild
-			// knows NOT to emit a second SessionFailed.
 			r.transitionOnFailure()
+			if ackErr != nil {
+				// Observation rejected the ack (stale session, etc.) — don't use
+				// sentinel. Return a regular error so ExecutePendingRebuild emits
+				// the fallback SessionFailed since observation didn't handle it.
+				return 0, fmt.Errorf("remote rebuild: session %d failed (observation rejected: %w)", r.SessionID, ackErr)
+			}
+			// Observation accepted the ack and already emitted SessionFailed.
+			// Use sentinel so ExecutePendingRebuild doesn't double-emit.
 			return 0, fmt.Errorf("remote rebuild: session %d: %w", r.SessionID, errRebuildAckFailed)
 		}
 	}
diff --git a/weed/server/block_recovery.go b/weed/server/block_recovery.go
index 349342200..af30c865c 100644
--- a/weed/server/block_recovery.go
+++ b/weed/server/block_recovery.go
@@ -582,6 +582,8 @@ func (rm *RecoveryManager) runRebuild(ctx context.Context, replicaID string, ass
 		Plan:             plan,
 		RebuildIO:        rebuildIO,
 	}
+	glog.V(0).Infof("recovery: storing pending rebuild replicaID=%s targetLSN=%d IO=%T",
+		replicaID, plan.RebuildTargetLSN, rebuildIO)
 	rm.coord.Store(replicaID, pe)
 	if rm.OnPendingExecution != nil {
 		rm.OnPendingExecution(rctx.volPath, pe)
@@ -605,8 +607,12 @@ func (rm *RecoveryManager) ExecutePendingCatchUp(replicaID string, targetLSN uin
 func (rm *RecoveryManager) ExecutePendingRebuild(replicaID string, targetLSN uint64) error {
 	pe := rm.coord.TakeRebuild(replicaID, targetLSN)
 	if pe == nil || pe.Driver == nil || pe.Plan == nil {
+		glog.V(0).Infof("recovery: ExecutePendingRebuild(%s, target=%d) — TakeRebuild returned nil (replicaID or targetLSN mismatch)",
+			replicaID, targetLSN)
 		return nil
 	}
+	glog.V(0).Infof("recovery: ExecutePendingRebuild(%s, target=%d) — executing with IO=%T",
+		replicaID, targetLSN, pe.RebuildIO)
 	err := rt.ExecuteRebuildPlan(pe.Driver, pe.Plan, pe.RebuildIO, pe.VolumeID, pe.ReplicaID, rm)
 	if err != nil {
 		glog.Warningf("recovery: rebuild execution failed for %s: %v", replicaID, err)
@@ -664,23 +670,21 @@ func (rm *RecoveryManager) OnRebuildCompleted(volumeID, replicaID string, plan *
 	if rm.bs == nil || rm.bs.v2Core == nil {
 		return
 	}
-	// For remote rebuilds, use the replica's achieved LSN (stored by onAck
-	// callback on SessionAckCompleted) instead of reading the primary's local
-	// vol — the primary's vol is the source, not the rebuilt destination.
+	// For remote rebuilds, the ack observation (ObserveReplicaRebuildSessionAck)
+	// already emitted SessionCompleted on SessionAckCompleted. Emitting
+	// RebuildCommitted here would cause a double completion in the engine.
+	// Consume the remote marker and skip.
 	rm.mu.Lock()
-	remoteAchieved, isRemote := rm.remoteRebuildAchieved[replicaID]
-	delete(rm.remoteRebuildAchieved, replicaID) // consumed
+	_, isRemote := rm.remoteRebuildAchieved[replicaID]
+	delete(rm.remoteRebuildAchieved, replicaID)
 	rm.mu.Unlock()
-
-	var status rt.RebuildCompletionStatus
 	if isRemote {
-		// Use replica's completion proof. CommittedLSN = CheckpointLSN = achievedLSN.
-		status.CommittedLSN = remoteAchieved
-		status.CheckpointLSN = remoteAchieved
-	} else {
-		// Legacy/local path: read from primary vol (backwards compat).
-		status = rm.readRebuildStatus(volumeID)
+		glog.V(0).Infof("recovery: remote rebuild %s — skipping RebuildCommitted (ack observation already emitted SessionCompleted)", replicaID)
+		return
 	}
+
+	// Legacy/local path: read from primary vol and emit RebuildCommitted.
+	status := rm.readRebuildStatus(volumeID)
 	ev := rt.DeriveRebuildCommitted(volumeID, replicaID, status, plan)
 	rm.bs.applyCoreEvent(ev)
 }