fix cluster: hashRing stale after rebalance, GetShardMap empty, loops, and migration no-op

- GetShardMap: copy Shards and Nodes map contents before returning
- hashRing: rebuild from shardMap.Nodes after every rebalance/shard_map update
- DistributedVM.handleRebalanceRequest: add leader check and self-broadcast guard
- route_message: add hop-count (MaxRouteHops=10) to prevent infinite loops
- handleMigrationRequest: broadcast migration updates instead of setting local copy

cluster/distributed.go

@@ -150,6 +150,15 @@ func (dvm *DistributedVM) SendMessage(message RuntimeMessage) error {
 
 // routeMessageToNode sends a message to another node for delivery to the target actor
 func (dvm *DistributedVM) routeMessageToNode(actorID string, message RuntimeMessage) error {
+	hops := 0
+	if mp, ok := message.(*MessagePayload); ok {
+		hops = mp.Hops
+	}
+	if hops >= MaxRouteHops {
+		dvm.cluster.logger.Printf("Dropping message for actor %s: exceeded max hops (%d)", actorID, MaxRouteHops)
+		return fmt.Errorf("message exceeded max hops")
+	}
+
 	msg := ClusterMessage{
 		Type: "route_message",
 		From: dvm.nodeID,
@@ -157,6 +166,7 @@ func (dvm *DistributedVM) routeMessageToNode(actorID string, message RuntimeMess
 		Payload: MessagePayload{
 			TargetActorID: actorID,
 			Type:          message.GetType(),
+			Hops:          hops + 1,
 		},
 		Timestamp: time.Now(),
 	}
@@ -220,6 +230,11 @@ func (dvm *DistributedVM) handleClusterMessage(msg *nats.Msg) {
 			return
 		}
 
+		if message.Hops >= MaxRouteHops {
+			dvm.cluster.logger.Printf("Dropping message for actor %s: exceeded max hops (%d)", message.TargetActorID, MaxRouteHops)
+			return
+		}
+
 		targetActor := message.TargetActorID
 		if dvm.IsLocalActor(targetActor) {
 			dvm.localRuntime.SendMessage(&message)
@@ -236,6 +251,15 @@ func (dvm *DistributedVM) handleClusterMessage(msg *nats.Msg) {
 
 // handleRebalanceRequest processes shard rebalancing requests
 func (dvm *DistributedVM) handleRebalanceRequest(msg ClusterMessage) {
+	if msg.From == dvm.nodeID {
+		return
+	}
+
+	if !dvm.cluster.IsLeader() {
+		dvm.cluster.logger.Printf("Ignoring rebalance request: not the leader")
+		return
+	}
+
 	payloadBytes, err := json.Marshal(msg.Payload)
 	if err != nil {
 		dvm.cluster.logger.Printf("Failed to marshal rebalance payload: %v", err)
@@ -251,6 +275,10 @@ func (dvm *DistributedVM) handleRebalanceRequest(msg ClusterMessage) {
 	dvm.cluster.mutex.Lock()
 	if newShardMap.Version > dvm.cluster.shardMap.Version {
 		dvm.cluster.shardMap = &newShardMap
+		dvm.cluster.hashRing = NewConsistentHashRing()
+		for nodeID := range newShardMap.Nodes {
+			dvm.cluster.hashRing.AddNode(nodeID)
+		}
 		dvm.cluster.logger.Printf("Applied new shard map (version %d) from rebalance", newShardMap.Version)
 	} else {
 		dvm.cluster.logger.Printf("Ignoring stale shard map (got version %d, current %d)",