diff --git a/server/store/group_message_runtime.go b/server/store/group_message_runtime.go
index 3f0260a..33b2d72 100644
--- a/server/store/group_message_runtime.go
+++ b/server/store/group_message_runtime.go
@@ -851,7 +851,7 @@ func (r *redisGroupMessageRuntime) StartRealtimeFanoutSubscriber(ctx context.Con
 					continue
 				}
 				if envelope.TenantID.IsValid() && envelope.DedupKey != "" {
-					id := fmt.Sprintf("%d:%s", envelope.TenantID, envelope.DedupKey)
+					id := realtimeFanoutDedupClaimID(envelope.TenantID, nodeID, envelope.DedupKey)
 					claimed, err := r.ClaimShortState("rt_dedup", id, 5*time.Minute)
 					if err != nil || !claimed {
 						continue
@@ -1110,6 +1110,13 @@ func (r *redisGroupMessageRuntime) realtimeFanoutPattern() string {
 	return strings.TrimSuffix(r.prefix, ":") + ":*:rt:fanout"
 }
 
+func realtimeFanoutDedupClaimID(tenantID types.TenantID, nodeID, dedupKey string) string {
+	if nodeID == "" {
+		nodeID = "local"
+	}
+	return fmt.Sprintf("%d:%s:%s", tenantID, nodeID, dedupKey)
+}
+
 func (r *redisGroupMessageRuntime) objectCacheKey(tenantID types.TenantID, namespace, id string) string {
 	return r.key(tenantID, "cache", namespace, id)
 }
diff --git a/server/store/group_message_runtime_test.go b/server/store/group_message_runtime_test.go
index bb57127..0fdd6bf 100644
--- a/server/store/group_message_runtime_test.go
+++ b/server/store/group_message_runtime_test.go
@@ -191,6 +191,20 @@ func TestLoginTokenRevocation(t *testing.T) {
 	}
 }
 
+func TestRealtimeFanoutDedupClaimIDIsNodeScoped(t *testing.T) {
+	tenantID := types.TenantID(7)
+	dedupKey := "data:p2pABC:42"
+
+	nodeA := realtimeFanoutDedupClaimID(tenantID, "pod-a", dedupKey)
+	nodeB := realtimeFanoutDedupClaimID(tenantID, "pod-b", dedupKey)
+	if nodeA == nodeB {
+		t.Fatalf("dedup claim id must be node-scoped: %q", nodeA)
+	}
+	if got, want := realtimeFanoutDedupClaimID(tenantID, "", dedupKey), "7:local:data:p2pABC:42"; got != want {
+		t.Fatalf("unexpected local fallback claim id: got %q want %q", got, want)
+	}
+}
+
 func TestMessageRuntimeSeqAndClientMidIdempotency(t *testing.T) {
 	oldRuntime := groupMsgRuntime
 	runtime := newTestGroupMessageRuntime()