Fix type assertion bug in handleClusterMessage

JSON unmarshal produces map[string]interface{}, not concrete types.
Added ModelPayload and MessagePayload concrete types that implement
RuntimeModel and RuntimeMessage interfaces respectively.

The handleClusterMessage now re-marshals and unmarshals the payload
to convert from map[string]interface{} to the proper concrete type.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cluster/distributed.go

@@ -177,18 +177,29 @@ func (dvm *DistributedVM) handleClusterMessage(msg *nats.Msg) {
 	switch clusterMsg.Type {
 	case "load_model":
 		// Handle model loading from other nodes
-		// Note: Payload comes as interface{} from JSON, need type assertion
-		// In practice, this would deserialize to the proper model type
-		if model, ok := clusterMsg.Payload.(RuntimeModel); ok {
-			dvm.localRuntime.LoadModel(model)
+		// Re-marshal and unmarshal to convert map[string]interface{} to concrete type
+		payloadBytes, err := json.Marshal(clusterMsg.Payload)
+		if err != nil {
+			return
 		}
+		var model ModelPayload
+		if err := json.Unmarshal(payloadBytes, &model); err != nil {
+			return
+		}
+		dvm.localRuntime.LoadModel(&model)
 
 	case "route_message":
 		// Handle message routing from other nodes
-		// Note: Similar type handling needed here
-		if message, ok := clusterMsg.Payload.(RuntimeMessage); ok {
-			dvm.localRuntime.SendMessage(message)
+		// Re-marshal and unmarshal to convert map[string]interface{} to concrete type
+		payloadBytes, err := json.Marshal(clusterMsg.Payload)
+		if err != nil {
+			return
 		}
+		var message MessagePayload
+		if err := json.Unmarshal(payloadBytes, &message); err != nil {
+			return
+		}
+		dvm.localRuntime.SendMessage(&message)
 
 	case "rebalance":
 		// Handle shard rebalancing requests

cluster/types.go

@@ -177,3 +177,29 @@ type RuntimeMessage interface {
 	// GetType returns the message type identifier
 	GetType() string
 }
+
+// ModelPayload is a concrete type for JSON-unmarshaling RuntimeModel payloads.
+// Use this when receiving model data over the network.
+type ModelPayload struct {
+	ID   string `json:"id"`
+	Name string `json:"name"`
+}
+
+// GetID implements RuntimeModel
+func (m *ModelPayload) GetID() string { return m.ID }
+
+// GetName implements RuntimeModel
+func (m *ModelPayload) GetName() string { return m.Name }
+
+// MessagePayload is a concrete type for JSON-unmarshaling RuntimeMessage payloads.
+// Use this when receiving message data over the network.
+type MessagePayload struct {
+	TargetActorID string `json:"targetActorId"`
+	Type          string `json:"type"`
+}
+
+// GetTargetActorID implements RuntimeMessage
+func (m *MessagePayload) GetTargetActorID() string { return m.TargetActorID }
+
+// GetType implements RuntimeMessage
+func (m *MessagePayload) GetType() string { return m.Type }