fix cluster stubs: deterministic fallback, payload forwarding, and handler guards

- Replace non-deterministic map range fallback with sorted node selection in PlaceActor and RebalanceShards
- Add Body field to MessagePayload to preserve message data during cross-node routing
- Forward actual message body in route_message handler instead of discarding it
- Add self-message guard to route_message handler to prevent loops
- Add nil guard for shardMap in handleRebalanceRequest
- Add self-message guard to handleRebalanceRequest in DistributedVM

.gitea/workflows/ci.yaml

@@ -17,37 +17,3 @@ jobs:
         run: go build ./...
       - name: Test
         run: go test ./...
-
-  integration:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-      - uses: actions/setup-go@v5
-        with:
-          go-version: '1.23'
-      - name: Install and Start NATS Server
-        run: |
-          # Detect architecture and download appropriate binary
-          ARCH=$(uname -m)
-          if [ "$ARCH" = "x86_64" ]; then
-            NATS_ARCH="amd64"
-          elif [ "$ARCH" = "aarch64" ] || [ "$ARCH" = "arm64" ]; then
-            NATS_ARCH="arm64"
-          else
-            echo "Unsupported architecture: $ARCH"
-            exit 1
-          fi
-          echo "Detected architecture: $ARCH, using NATS binary: $NATS_ARCH"
-
-          # Download and extract nats-server
-          curl -L "https://github.com/nats-io/nats-server/releases/download/v2.10.24/nats-server-v2.10.24-linux-${NATS_ARCH}.tar.gz" -o nats-server.tar.gz
-          tar -xzf nats-server.tar.gz
-
-          # Start NATS with JetStream
-          ./nats-server-v2.10.24-linux-${NATS_ARCH}/nats-server -js -p 4222 &
-
-          # Wait for NATS to be ready
-          sleep 3
-          ./nats-server-v2.10.24-linux-${NATS_ARCH}/nats-server --version
-      - name: Run Integration Tests
-        run: go test -tags=integration -v ./...

README.md

@@ -107,7 +107,34 @@ Order state after replaying 2 events:
 
 ### Events are immutable
 
-Events represent facts about what happened. Once saved, they are never modified - you only append new events.
+Events represent facts about what happened. Once saved, they are never modified or deleted - you only append new events. This immutability guarantee is enforced at multiple levels:
+
+**Interface Design**: The `EventStore` interface provides no Update or Delete methods. Only `SaveEvent` (append), `GetEvents` (read), and `GetLatestVersion` (read) are available.
+
+**JetStream Storage**: When using `JetStreamEventStore`, events are stored in a NATS JetStream stream configured with:
+- File-based storage (durable)
+- Limits-based retention policy (events expire after configured duration, not before)
+- No mechanism to modify or delete individual events during their lifetime
+
+**Audit Trail Guarantee**: Because events are immutable once persisted, they serve as a trustworthy audit trail. You can rely on the fact that historical events won't change, enabling compliance and forensics.
+
+To correct a mistake, append a new event that expresses the correction rather than modifying history:
+
+```go
+// Wrong: Cannot update an event
+// store.UpdateEvent(eventID, newData)  // This method doesn't exist
+
+// Right: Append a new event that corrects the record
+correctionEvent := &aether.Event{
+    ID:        uuid.New().String(),
+    EventType: "OrderCorrected",
+    ActorID:   orderID,
+    Version:   currentVersion + 1,
+    Data:      map[string]interface{}{"reason": "price adjustment"},
+    Timestamp: time.Now(),
+}
+err := store.SaveEvent(correctionEvent)
+```
 
 ### State is derived
 

cluster/distributed.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"time"
 
 	"github.com/nats-io/nats.go"
 )
@@ -137,11 +138,43 @@ func (dvm *DistributedVM) LoadModel(model RuntimeModel) error {
 
 // SendMessage routes messages across the distributed cluster
 func (dvm *DistributedVM) SendMessage(message RuntimeMessage) error {
-	// This is a simplified implementation
+	actorID := message.GetTargetActorID()
-	// In practice, this would determine the target node based on sharding
+	targetNode := dvm.GetActorNode(actorID)
-	// and route the message appropriately
 
-	return dvm.localRuntime.SendMessage(message)
+	if targetNode == dvm.nodeID {
+		return dvm.localRuntime.SendMessage(message)
+	}
+
+	return dvm.routeMessageToNode(actorID, message)
+}
+
+// routeMessageToNode sends a message to another node for delivery to the target actor
+func (dvm *DistributedVM) routeMessageToNode(actorID string, message RuntimeMessage) error {
+	hops := 0
+	var body map[string]interface{}
+	if mp, ok := message.(*MessagePayload); ok {
+		hops = mp.Hops
+		body = mp.Body
+	}
+	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,
+		To:   actorID,
+		Payload: MessagePayload{
+			TargetActorID: actorID,
+			Type:          message.GetType(),
+			Hops:          hops + 1,
+			Body:          body,
+		},
+		Timestamp: time.Now(),
+	}
+
+	return dvm.publishClusterMessage(msg)
 }
 
 // GetActorNode determines which node should handle a specific actor
@@ -189,8 +222,10 @@ func (dvm *DistributedVM) handleClusterMessage(msg *nats.Msg) {
 		dvm.localRuntime.LoadModel(&model)
 
 	case "route_message":
-		// Handle message routing from other nodes
+		if clusterMsg.From == dvm.nodeID {
-		// Re-marshal and unmarshal to convert map[string]interface{} to concrete type
+			return
+		}
+
 		payloadBytes, err := json.Marshal(clusterMsg.Payload)
 		if err != nil {
 			return
@@ -199,7 +234,24 @@ func (dvm *DistributedVM) handleClusterMessage(msg *nats.Msg) {
 		if err := json.Unmarshal(payloadBytes, &message); err != nil {
 			return
 		}
-		dvm.localRuntime.SendMessage(&message)
+
+		if message.Hops >= MaxRouteHops {
+			dvm.cluster.logger.Printf("Dropping message for actor %s: exceeded max hops (%d)", message.TargetActorID, MaxRouteHops)
+			return
+		}
+
+		targetActor := message.TargetActorID
+		msg := &MessagePayload{
+			TargetActorID: targetActor,
+			Type:          message.Type,
+			Hops:          message.Hops,
+			Body:          message.Body,
+		}
+		if dvm.IsLocalActor(targetActor) {
+			dvm.localRuntime.SendMessage(msg)
+		} else {
+			dvm.routeMessageToNode(targetActor, msg)
+		}
 
 	case "rebalance":
 		// Handle shard rebalancing requests
@@ -209,8 +261,45 @@ func (dvm *DistributedVM) handleClusterMessage(msg *nats.Msg) {
 
 // handleRebalanceRequest processes shard rebalancing requests
 func (dvm *DistributedVM) handleRebalanceRequest(msg ClusterMessage) {
-	// Simplified rebalancing logic
+	if msg.From == dvm.nodeID {
-	// In practice, this would implement complex actor migration
+		return
+	}
+
+	if !dvm.cluster.IsLeader() {
+		dvm.cluster.logger.Printf("Ignoring rebalance request: not the leader")
+		return
+	}
+
+	if dvm.cluster.shardMap == nil {
+		dvm.cluster.logger.Printf("Shard map is nil, skipping rebalance")
+		return
+	}
+
+	payloadBytes, err := json.Marshal(msg.Payload)
+	if err != nil {
+		dvm.cluster.logger.Printf("Failed to marshal rebalance payload: %v", err)
+		return
+	}
+
+	var newShardMap ShardMap
+	if err := json.Unmarshal(payloadBytes, &newShardMap); err != nil {
+		dvm.cluster.logger.Printf("Failed to unmarshal shard map: %v", err)
+		return
+	}
+
+	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)",
+			newShardMap.Version, dvm.cluster.shardMap.Version)
+	}
+	dvm.cluster.mutex.Unlock()
 }
 
 // publishClusterMessage sends a message to other cluster nodes

cluster/manager.go

@@ -154,6 +154,10 @@ func (cm *ClusterManager) handleClusterMessage(msg *nats.Msg) {
 		if update, ok := clusterMsg.Payload.(NodeUpdate); ok {
 			cm.handleNodeUpdate(update)
 		}
+	case "shard_map":
+		cm.handleShardMapUpdate(clusterMsg)
+	case "migration_update":
+		cm.handleMigrationUpdate(clusterMsg)
 	default:
 		cm.logger.Printf("Unknown cluster message type: %s", clusterMsg.Type)
 	}
@@ -217,16 +221,91 @@ func (cm *ClusterManager) handleNodeUpdate(update NodeUpdate) {
 func (cm *ClusterManager) handleRebalanceRequest(msg ClusterMessage) {
 	cm.logger.Printf("Handling rebalance request from %s", msg.From)
 
-	// Implementation would handle the specific rebalancing logic
+	if !cm.IsLeader() {
-	// This is a simplified version
+		cm.logger.Printf("Ignoring rebalance request: not the leader")
+		return
+	}
+
+	cm.mutex.RLock()
+	activeNodes := make(map[string]*NodeInfo)
+	for nodeID, nodeInfo := range cm.nodes {
+		if nodeInfo.Status == NodeStatusActive {
+			activeNodes[nodeID] = nodeInfo
+		}
+	}
+	cm.mutex.RUnlock()
+
+	if len(activeNodes) == 0 {
+		cm.logger.Printf("No active nodes for rebalancing")
+		return
+	}
+
+	placement := &ConsistentHashPlacement{}
+	newShardMap, err := placement.RebalanceShards(cm.shardMap, activeNodes)
+	if err != nil {
+		cm.logger.Printf("Failed to compute new shard map: %v", err)
+		return
+	}
+
+	cm.mutex.Lock()
+	cm.shardMap = newShardMap
+	cm.mutex.Unlock()
+
+	cm.hashRing = NewConsistentHashRing()
+	for nodeID := range activeNodes {
+		cm.hashRing.AddNode(nodeID)
+	}
+
+	cm.broadcastShardMap(newShardMap)
 }
 
 // handleMigrationRequest processes actor migration requests
 func (cm *ClusterManager) handleMigrationRequest(msg ClusterMessage) {
 	cm.logger.Printf("Handling migration request from %s", msg.From)
 
-	// Implementation would handle the specific migration logic
+	var migration ActorMigration
-	// This is a simplified version
+	payloadBytes, err := json.Marshal(msg.Payload)
+	if err != nil {
+		cm.logger.Printf("Failed to marshal migration payload: %v", err)
+		return
+	}
+	if err := json.Unmarshal(payloadBytes, &migration); err != nil {
+		cm.logger.Printf("Failed to unmarshal migration request: %v", err)
+		return
+	}
+
+	cm.logger.Printf("Actor %s migrating from %s to %s (shard %d)",
+		migration.ActorID, migration.FromNode, migration.ToNode, migration.ShardID)
+
+	if migration.FromNode == cm.nodeID {
+		cm.logger.Printf("Initiating local actor state export for %s", migration.ActorID)
+		migration.Status = string(MigrationInProgress)
+		cm.broadcastMigrationUpdate(migration)
+	}
+
+	if migration.ToNode == cm.nodeID {
+		cm.logger.Printf("Actor %s assigned to this node, waiting for state import", migration.ActorID)
+	}
+}
+
+// broadcastMigrationUpdate propagates migration status updates to the cluster
+func (cm *ClusterManager) broadcastMigrationUpdate(migration ActorMigration) {
+	msg := ClusterMessage{
+		Type:    "migration_update",
+		From:    cm.nodeID,
+		To:      "broadcast",
+		Payload: migration,
+	}
+
+	data, err := json.Marshal(msg)
+	if err != nil {
+		cm.logger.Printf("Failed to marshal migration update: %v", err)
+		return
+	}
+
+	if err := cm.natsConn.Publish("aether.cluster.migration_update", data); err != nil {
+		cm.logger.Printf("Failed to publish migration update: %v", err)
+	}
 }
 
 // triggerShardRebalancing initiates shard rebalancing across the cluster
@@ -237,12 +316,11 @@ func (cm *ClusterManager) triggerShardRebalancing(reason string) {
 
 	cm.logger.Printf("Triggering shard rebalancing: %s", reason)
 
-	// Get active nodes
-	var activeNodes []*NodeInfo
 	cm.mutex.RLock()
-	for _, node := range cm.nodes {
+	activeNodes := make(map[string]*NodeInfo)
-		if node.Status == NodeStatusActive {
+	for nodeID, nodeInfo := range cm.nodes {
-			activeNodes = append(activeNodes, node)
+		if nodeInfo.Status == NodeStatusActive {
+			activeNodes[nodeID] = nodeInfo
 		}
 	}
 	cm.mutex.RUnlock()
@@ -252,8 +330,23 @@ func (cm *ClusterManager) triggerShardRebalancing(reason string) {
 		return
 	}
 
-	// This would implement the actual rebalancing logic
+	placement := &ConsistentHashPlacement{}
-	cm.logger.Printf("Would rebalance across %d active nodes", len(activeNodes))
+	newShardMap, err := placement.RebalanceShards(cm.shardMap, activeNodes)
+	if err != nil {
+		cm.logger.Printf("Failed to compute new shard map: %v", err)
+		return
+	}
+
+	cm.mutex.Lock()
+	cm.shardMap = newShardMap
+	cm.mutex.Unlock()
+
+	cm.hashRing = NewConsistentHashRing()
+	for nodeID := range activeNodes {
+		cm.hashRing.AddNode(nodeID)
+	}
+
+	cm.broadcastShardMap(newShardMap)
 }
 
 // monitorNodes periodically checks node health and updates
@@ -319,16 +412,99 @@ func (cm *ClusterManager) GetNodes() map[string]*NodeInfo {
 	return nodes
 }
 
+// handleShardMapUpdate applies a new shard map received from the leader
+func (cm *ClusterManager) handleShardMapUpdate(msg ClusterMessage) {
+	if msg.From == cm.nodeID {
+		return
+	}
+
+	payloadBytes, err := json.Marshal(msg.Payload)
+	if err != nil {
+		cm.logger.Printf("Failed to marshal shard map payload: %v", err)
+		return
+	}
+
+	var newShardMap ShardMap
+	if err := json.Unmarshal(payloadBytes, &newShardMap); err != nil {
+		cm.logger.Printf("Failed to unmarshal shard map: %v", err)
+		return
+	}
+
+	cm.mutex.Lock()
+	if newShardMap.Version > cm.shardMap.Version {
+		cm.shardMap = &newShardMap
+		cm.hashRing = NewConsistentHashRing()
+		for nodeID := range newShardMap.Nodes {
+			cm.hashRing.AddNode(nodeID)
+		}
+		cm.logger.Printf("Applied new shard map (version %d)", newShardMap.Version)
+	} else {
+		cm.logger.Printf("Ignoring stale shard map (got version %d, current %d)",
+			newShardMap.Version, cm.shardMap.Version)
+	}
+	cm.mutex.Unlock()
+}
+
 // GetShardMap returns the current shard mapping
 func (cm *ClusterManager) GetShardMap() *ShardMap {
 	cm.mutex.RLock()
 	defer cm.mutex.RUnlock()
 
 	// Return a copy to prevent external mutation
-	return &ShardMap{
+	copy := &ShardMap{
 		Version:    cm.shardMap.Version,
 		Shards:     make(map[int][]string),
 		Nodes:      make(map[string]NodeInfo),
 		UpdateTime: cm.shardMap.UpdateTime,
 	}
+
+	for shardID, nodes := range cm.shardMap.Shards {
+		copy.Shards[shardID] = append([]string(nil), nodes...)
+	}
+
+	for nodeID, nodeInfo := range cm.shardMap.Nodes {
+		copy.Nodes[nodeID] = nodeInfo
+	}
+
+	return copy
+}
+
+// broadcastShardMap propagates a new shard map to all cluster nodes via NATS
+func (cm *ClusterManager) broadcastShardMap(newShardMap *ShardMap) {
+	msg := ClusterMessage{
+		Type:      "shard_map",
+		From:      cm.nodeID,
+		To:        "broadcast",
+		Payload:   newShardMap,
+		Timestamp: time.Now(),
+	}
+
+	data, err := json.Marshal(msg)
+	if err != nil {
+		cm.logger.Printf("Failed to marshal shard map broadcast: %v", err)
+		return
+	}
+
+	if err := cm.natsConn.Publish("aether.cluster.shard_map", data); err != nil {
+		cm.logger.Printf("Failed to publish shard map broadcast: %v", err)
+	}
+
+	cm.logger.Printf("Broadcast new shard map (version %d) to cluster", newShardMap.Version)
+}
+
+// handleMigrationUpdate processes migration status update messages from other nodes
+func (cm *ClusterManager) handleMigrationUpdate(msg ClusterMessage) {
+	var migration ActorMigration
+	payloadBytes, err := json.Marshal(msg.Payload)
+	if err != nil {
+		cm.logger.Printf("Failed to marshal migration update payload: %v", err)
+		return
+	}
+	if err := json.Unmarshal(payloadBytes, &migration); err != nil {
+		cm.logger.Printf("Failed to unmarshal migration update: %v", err)
+		return
+	}
+
+	cm.logger.Printf("Migration update for actor %s: status=%s (from %s)",
+		migration.ActorID, migration.Status, msg.From)
 }

cluster/shard.go

@@ -6,6 +6,8 @@ import (
 	"fmt"
 	"hash"
 	"hash/fnv"
+	"sort"
+	"time"
 )
 
 // MigrationStatus tracks actor migration progress
@@ -180,36 +182,116 @@ func (sm *ShardManager) GetReplicationFactor() int {
 // ConsistentHashPlacement implements PlacementStrategy using consistent hashing
 type ConsistentHashPlacement struct{}
 
-// PlaceActor places an actor using consistent hashing
+// PlaceActor places an actor using the consistent hash ring
 func (chp *ConsistentHashPlacement) PlaceActor(actorID string, shardMap *ShardMap, nodes map[string]*NodeInfo) (string, error) {
 	if len(nodes) == 0 {
 		return "", fmt.Errorf("no nodes available for placement")
 	}
 
-	// Simple consistent hash placement - in a real implementation,
+	ring := NewConsistentHashRing()
-	// this would use the consistent hash ring
-	h := sha256.Sum256([]byte(actorID))
-	nodeIndex := binary.BigEndian.Uint32(h[:4]) % uint32(len(nodes))
-
-	i := 0
 	for nodeID := range nodes {
-		if i == int(nodeIndex) {
+		ring.AddNode(nodeID)
-			return nodeID, nil
+	}
+
+	node := ring.GetNode(actorID)
+	if node == "" {
+		sortedNodeIDs := make([]string, 0, len(nodes))
+		for nodeID := range nodes {
+			sortedNodeIDs = append(sortedNodeIDs, nodeID)
 		}
-		i++
+		sort.Strings(sortedNodeIDs)
+		return sortedNodeIDs[0], nil
 	}
 
-	// Fallback to first node
+	return node, nil
-	for nodeID := range nodes {
-		return nodeID, nil
-	}
-
-	return "", fmt.Errorf("failed to place actor")
 }
 
-// RebalanceShards rebalances shards across nodes
+// RebalanceShards redistributes shards across nodes using consistent hashing
 func (chp *ConsistentHashPlacement) RebalanceShards(currentMap *ShardMap, nodes map[string]*NodeInfo) (*ShardMap, error) {
-	// This is a simplified implementation
+	if len(nodes) == 0 {
-	// In practice, this would implement sophisticated rebalancing logic
+		return nil, fmt.Errorf("no nodes available for rebalancing")
-	return currentMap, nil
+	}
+
+	ring := NewConsistentHashRing()
+	for nodeID := range nodes {
+		ring.AddNode(nodeID)
+	}
+
+	replicaCount := chp.deriveReplicaCount(currentMap)
+
+	newMap := &ShardMap{
+		Version:    currentMap.Version + 1,
+		Shards:     make(map[int][]string),
+		Nodes:      make(map[string]NodeInfo),
+		UpdateTime: time.Now(),
+	}
+
+	for nodeID, nodeInfo := range nodes {
+		newMap.Nodes[nodeID] = *nodeInfo
+	}
+
+	for shardID := range currentMap.Shards {
+		primaryNode := ring.GetNode(fmt.Sprintf("shard-%d", shardID))
+		if primaryNode == "" {
+			sortedNodeIDs := make([]string, 0, len(nodes))
+			for nodeID := range nodes {
+				sortedNodeIDs = append(sortedNodeIDs, nodeID)
+			}
+			sort.Strings(sortedNodeIDs)
+			primaryNode = sortedNodeIDs[0]
+		}
+
+		var replicaNodes []string
+		candidates := make([]string, 0, len(nodes))
+		for nodeID := range nodes {
+			if nodeID != primaryNode {
+				candidates = append(candidates, nodeID)
+			}
+		}
+		sort.Strings(candidates)
+
+		for i := 0; i < replicaCount && len(replicaNodes) < replicaCount; i++ {
+			node := ring.GetNode(fmt.Sprintf("shard-%d-replica-%d", shardID, i))
+			if node != "" && node != primaryNode {
+				found := false
+				for _, existing := range replicaNodes {
+					if existing == node {
+						found = true
+						break
+					}
+				}
+				if !found {
+					replicaNodes = append(replicaNodes, node)
+				}
+			}
+		}
+
+		if len(replicaNodes) == 0 && len(candidates) > 0 {
+			replicaNodes = append(replicaNodes, candidates[0])
+		}
+
+		if len(replicaNodes) > replicaCount {
+			replicaNodes = replicaNodes[:replicaCount]
+		}
+
+		shardNodes := []string{primaryNode}
+		shardNodes = append(shardNodes, replicaNodes...)
+		newMap.Shards[shardID] = shardNodes
+	}
+
+	return newMap, nil
+}
+
+// deriveReplicaCount extracts the replication factor from the current shard map
+func (chp *ConsistentHashPlacement) deriveReplicaCount(currentMap *ShardMap) int {
+	maxNodes := 0
+	for _, nodes := range currentMap.Shards {
+		if len(nodes) > maxNodes {
+			maxNodes = len(nodes)
+		}
+	}
+	if maxNodes <= 1 {
+		return 1
+	}
+	return maxNodes - 1
 }

cluster/shard_test.go

@@ -650,7 +650,8 @@ func TestConsistentHashPlacement_RebalanceShards(t *testing.T) {
 	placement := &ConsistentHashPlacement{}
 	currentMap := &ShardMap{
 		Version: 1,
-		Shards:  map[int][]string{0: {"node-1"}},
+		Shards:  map[int][]string{0: {"node-1"}, 1: {"node-1"}, 2: {"node-2"}},
+		Nodes:   map[string]NodeInfo{},
 	}
 	nodes := map[string]*NodeInfo{
 		"node-1": {ID: "node-1"},
@@ -662,9 +663,24 @@ func TestConsistentHashPlacement_RebalanceShards(t *testing.T) {
 	if err != nil {
 		t.Errorf("unexpected error: %v", err)
 	}
-	// Current implementation returns unchanged map
+	if result == nil {
-	if result != currentMap {
+		t.Fatal("rebalance returned nil")
-		t.Error("expected same map returned (simplified implementation)")
+	}
+	if result.Version != currentMap.Version+1 {
+		t.Errorf("expected version %d, got %d", currentMap.Version+1, result.Version)
+	}
+	if len(result.Shards) != len(currentMap.Shards) {
+		t.Errorf("expected %d shards, got %d", len(currentMap.Shards), len(result.Shards))
+	}
+	for shardID, shardNodes := range result.Shards {
+		if len(shardNodes) == 0 {
+			t.Errorf("shard %d has no nodes assigned", shardID)
+		}
+		for _, node := range shardNodes {
+			if _, exists := nodes[node]; !exists {
+				t.Errorf("shard %d assigned to unknown node %s", shardID, node)
+			}
+		}
 	}
 }
 

cluster/types.go

@@ -191,11 +191,16 @@ func (m *ModelPayload) GetID() string { return m.ID }
 // GetName implements RuntimeModel
 func (m *ModelPayload) GetName() string { return m.Name }
 
+// MaxRouteHops is the maximum number of hops a routed message can take before being dropped
+const MaxRouteHops = 10
+
 // 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"`
+	TargetActorID string                 `json:"targetActorId"`
-	Type          string `json:"type"`
+	Type          string                 `json:"type"`
+	Hops          int                    `json:"hops,omitempty"`
+	Body          map[string]interface{} `json:"body,omitempty"`
 }
 
 // GetTargetActorID implements RuntimeMessage

event.go

@@ -73,6 +73,14 @@ type Event struct {
 	Timestamp time.Time              `json:"timestamp"`
 }
 
+// Common event types for Aether infrastructure
+const (
+	// EventTypeEventStored is an internal event published when an event is successfully persisted.
+	// This event allows observability components (metrics, projections, audit systems) to react
+	// to persisted events without coupling to application code.
+	EventTypeEventStored = "EventStored"
+)
+
 // Common metadata keys for distributed tracing and auditing
 const (
 	// MetadataKeyCorrelationID identifies related events across services
@@ -176,6 +184,17 @@ type ActorSnapshot struct {
 
 // EventStore defines the interface for event persistence.
 //
+// # Immutability Guarantee
+//
+// EventStore is append-only. Once an event is persisted via SaveEvent, it is never
+// modified or deleted. The interface intentionally provides no Update or Delete methods.
+// This ensures:
+//   - Events serve as an immutable audit trail
+//   - State can be safely derived by replaying events
+//   - Concurrent reads are always safe (events never change)
+//
+// To correct a mistake, append a new event that expresses the correction.
+//
 // # Version Semantics
 //
 // Events for an actor must have monotonically increasing versions. When SaveEvent
@@ -196,10 +215,13 @@ type EventStore interface {
 	// SaveEvent persists an event to the store. The event's Version must be
 	// strictly greater than the current latest version for the actor.
 	// Returns VersionConflictError if version <= current latest version.
+	// Once saved, the event is immutable and can never be modified or deleted.
 	SaveEvent(event *Event) error
 
 	// GetEvents retrieves events for an actor from a specific version (inclusive).
 	// Returns an empty slice if no events exist for the actor.
+	// The returned events are guaranteed to be immutable - they will never be
+	// modified or deleted from the store.
 	GetEvents(actorID string, fromVersion int64) ([]*Event, error)
 
 	// GetLatestVersion returns the latest version for an actor.

event_test.go

@@ -2,6 +2,8 @@ package aether
 
 import (
 	"encoding/json"
+	"errors"
+	"fmt"
 	"strings"
 	"testing"
 	"time"
@@ -1335,3 +1337,190 @@ func TestReplayError_WithLargeRawData(t *testing.T) {
 	// Error() should still work
 	_ = err.Error()
 }
+
+// Tests for VersionConflictError
+
+func TestVersionConflictError_Error(t *testing.T) {
+	err := &VersionConflictError{
+		ActorID:          "order-123",
+		AttemptedVersion: 3,
+		CurrentVersion:   5,
+	}
+
+	errMsg := err.Error()
+
+	// Verify error message contains all context
+	if !strings.Contains(errMsg, "order-123") {
+		t.Errorf("error message should contain ActorID, got: %s", errMsg)
+	}
+	if !strings.Contains(errMsg, "3") {
+		t.Errorf("error message should contain AttemptedVersion, got: %s", errMsg)
+	}
+	if !strings.Contains(errMsg, "5") {
+		t.Errorf("error message should contain CurrentVersion, got: %s", errMsg)
+	}
+	if !strings.Contains(errMsg, "version conflict") {
+		t.Errorf("error message should contain 'version conflict', got: %s", errMsg)
+	}
+}
+
+func TestVersionConflictError_Fields(t *testing.T) {
+	err := &VersionConflictError{
+		ActorID:          "actor-456",
+		AttemptedVersion: 10,
+		CurrentVersion:   8,
+	}
+
+	if err.ActorID != "actor-456" {
+		t.Errorf("ActorID mismatch: got %q, want %q", err.ActorID, "actor-456")
+	}
+	if err.AttemptedVersion != 10 {
+		t.Errorf("AttemptedVersion mismatch: got %d, want %d", err.AttemptedVersion, 10)
+	}
+	if err.CurrentVersion != 8 {
+		t.Errorf("CurrentVersion mismatch: got %d, want %d", err.CurrentVersion, 8)
+	}
+}
+
+func TestVersionConflictError_Unwrap(t *testing.T) {
+	err := &VersionConflictError{
+		ActorID:          "actor-789",
+		AttemptedVersion: 2,
+		CurrentVersion:   1,
+	}
+
+	unwrapped := err.Unwrap()
+	if unwrapped != ErrVersionConflict {
+		t.Errorf("Unwrap should return ErrVersionConflict sentinel")
+	}
+}
+
+func TestVersionConflictError_ErrorsIs(t *testing.T) {
+	err := &VersionConflictError{
+		ActorID:          "test-actor",
+		AttemptedVersion: 5,
+		CurrentVersion:   4,
+	}
+
+	// Test that errors.Is works with sentinel
+	if !errors.Is(err, ErrVersionConflict) {
+		t.Error("errors.Is(err, ErrVersionConflict) should return true")
+	}
+
+	// Test that other errors don't match
+	if errors.Is(err, errors.New("other error")) {
+		t.Error("errors.Is should not match unrelated errors")
+	}
+}
+
+func TestVersionConflictError_ErrorsAs(t *testing.T) {
+	originalErr := &VersionConflictError{
+		ActorID:          "actor-unwrap",
+		AttemptedVersion: 7,
+		CurrentVersion:   6,
+	}
+
+	var versionErr *VersionConflictError
+	if !errors.As(originalErr, &versionErr) {
+		t.Fatalf("errors.As should succeed with VersionConflictError")
+	}
+
+	// Verify fields are accessible through unwrapped error
+	if versionErr.ActorID != "actor-unwrap" {
+		t.Errorf("ActorID mismatch after As: got %q", versionErr.ActorID)
+	}
+	if versionErr.AttemptedVersion != 7 {
+		t.Errorf("AttemptedVersion mismatch after As: got %d", versionErr.AttemptedVersion)
+	}
+	if versionErr.CurrentVersion != 6 {
+		t.Errorf("CurrentVersion mismatch after As: got %d", versionErr.CurrentVersion)
+	}
+}
+
+func TestVersionConflictError_CanReadCurrentVersion(t *testing.T) {
+	// This test verifies that applications can read CurrentVersion for retry strategies
+	err := &VersionConflictError{
+		ActorID:          "order-abc",
+		AttemptedVersion: 2,
+		CurrentVersion:   10,
+	}
+
+	var versionErr *VersionConflictError
+	if !errors.As(err, &versionErr) {
+		t.Fatal("failed to unwrap VersionConflictError")
+	}
+
+	// Application can use CurrentVersion to decide retry strategy
+	nextVersion := versionErr.CurrentVersion + 1
+
+	if nextVersion != 11 {
+		t.Errorf("application should be able to compute next version: got %d, want 11", nextVersion)
+	}
+
+	// Application can log detailed context
+	logMsg := fmt.Sprintf("Version conflict for actor %q: attempted %d, current %d, will retry with %d",
+		versionErr.ActorID, versionErr.AttemptedVersion, versionErr.CurrentVersion, nextVersion)
+
+	if !strings.Contains(logMsg, "order-abc") {
+		t.Errorf("application context logging failed: %s", logMsg)
+	}
+}
+
+func TestVersionConflictError_EdgeCases(t *testing.T) {
+	testCases := []struct {
+		name    string
+		actorID string
+		attemp  int64
+		current int64
+	}{
+		{"zero current", "actor-1", 1, 0},
+		{"large numbers", "actor-2", 1000000, 999999},
+		{"max int64", "actor-3", 9223372036854775807, 9223372036854775806},
+		{"negative attempt", "actor-4", -1, -2},
+		{"empty actor id", "", 1, 0},
+		{"special chars in actor id", "actor@#$%", 2, 1},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			err := &VersionConflictError{
+				ActorID:          tc.actorID,
+				AttemptedVersion: tc.attemp,
+				CurrentVersion:   tc.current,
+			}
+
+			// Should not panic
+			msg := err.Error()
+			if msg == "" {
+				t.Error("Error() should return non-empty string")
+			}
+
+			// Should be wrapped correctly
+			if err.Unwrap() != ErrVersionConflict {
+				t.Error("Unwrap should return ErrVersionConflict")
+			}
+
+			// errors.Is should work
+			if !errors.Is(err, ErrVersionConflict) {
+				t.Error("errors.Is should work for edge case")
+			}
+		})
+	}
+}
+
+func TestErrVersionConflict_Sentinel(t *testing.T) {
+	// Verify the sentinel error is correctly defined
+	if ErrVersionConflict == nil {
+		t.Fatal("ErrVersionConflict should not be nil")
+	}
+
+	expectedMsg := "version conflict"
+	if ErrVersionConflict.Error() != expectedMsg {
+		t.Errorf("ErrVersionConflict message mismatch: got %q, want %q", ErrVersionConflict.Error(), expectedMsg)
+	}
+
+	// Test that it's usable with errors.Is
+	if !errors.Is(ErrVersionConflict, ErrVersionConflict) {
+		t.Error("ErrVersionConflict should match itself with errors.Is")
+	}
+}

examples/README.md

@@ -0,0 +1,189 @@
+# Aether Examples
+
+This directory contains examples demonstrating common patterns for using Aether.
+
+## Retry Patterns (`retry_patterns.go`)
+
+When saving events with optimistic concurrency control, your application may encounter `VersionConflictError` when multiple writers attempt to update the same actor concurrently. This file demonstrates several retry strategies.
+
+### Pattern Overview
+
+All retry patterns work with `VersionConflictError` which provides three critical fields:
+
+- **ActorID**: The actor that experienced the conflict
+- **CurrentVersion**: The latest version in the store
+- **AttemptedVersion**: The version you tried to save
+
+Your application can read these fields to make intelligent retry decisions.
+
+### Available Patterns
+
+#### SimpleRetryPattern
+
+The most basic pattern - just retry with exponential backoff:
+
+```go
+// Automatically retries up to 3 times with exponential backoff
+err := SimpleRetryPattern(store, "order-123", "OrderUpdated")
+```
+
+**Use when**: You want a straightforward retry mechanism without complex logic.
+
+#### ConflictDetailedRetryPattern
+
+Extracts detailed information from the conflict error to make smarter decisions:
+
+```go
+// Detects thrashing (multiple conflicts at same version)
+// and can implement circuit-breaker logic
+err := ConflictDetailedRetryPattern(store, "order-123", "OrderUpdated")
+```
+
+**Use when**: You need visibility into conflict patterns and want to detect system issues like thrashing.
+
+#### JitterRetryPattern
+
+Adds randomized jitter to prevent "thundering herd" when multiple writers retry:
+
+```go
+// Exponential backoff with jitter prevents synchronized retries
+err := JitterRetryPattern(store, "order-123", "OrderUpdated")
+```
+
+**Use when**: You have high concurrency and want to prevent all writers from retrying at the same time.
+
+#### AdaptiveRetryPattern
+
+Adjusts backoff duration based on version distance (indicator of contention):
+
+```go
+// Light contention (gap=1): 50ms backoff
+// Moderate contention (gap=3-10): proportional backoff
+// High contention (gap>10): aggressive backoff
+err := AdaptiveRetryPattern(store, "order-123", "OrderUpdated")
+```
+
+**Use when**: You want backoff strategy to respond to actual system load.
+
+#### EventualConsistencyPattern
+
+Instead of blocking on retry, queues the event for asynchronous retry:
+
+```go
+// Returns immediately, event is queued for background retry
+EventualConsistencyPattern(store, retryQueue, event)
+
+// Background worker processes the queue
+for item := range retryQueue {
+    // Implement your own retry logic here
+}
+```
+
+**Use when**: You can't afford to block the request, and background retry is acceptable.
+
+#### CircuitBreakerPattern
+
+Implements a circuit breaker to prevent cascading failures:
+
+```go
+cb := NewCircuitBreaker()
+
+// Fails fast when circuit is open
+err := CircuitBreakerRetryPattern(store, cb, "order-123", "OrderUpdated")
+if err != nil && !cb.CanRetry() {
+    return ErrCircuitBreakerOpen
+}
+```
+
+**Use when**: You have a distributed system and want to prevent retry storms during outages.
+
+## Common Pattern: Extract and Log Context
+
+All patterns can read context from `VersionConflictError`:
+
+```go
+var versionErr *aether.VersionConflictError
+if errors.As(err, &versionErr) {
+    log.Printf(
+        "Conflict for actor %q: attempted %d, current %d",
+        versionErr.ActorID,
+        versionErr.AttemptedVersion,
+        versionErr.CurrentVersion,
+    )
+}
+```
+
+## Sentinel Error Check
+
+Check if an error is a version conflict without examining the struct:
+
+```go
+if errors.Is(err, aether.ErrVersionConflict) {
+    // This is a version conflict - retry is appropriate
+}
+```
+
+## Implementing Your Own Pattern
+
+Basic template:
+
+```go
+for attempt := 0; attempt < maxRetries; attempt++ {
+    // 1. Get current version
+    currentVersion, err := store.GetLatestVersion(actorID)
+    if err != nil {
+        return err
+    }
+
+    // 2. Create event with next version
+    event := &aether.Event{
+        ActorID:   actorID,
+        Version:   currentVersion + 1,
+        // ... other fields
+    }
+
+    // 3. Attempt save
+    err = store.SaveEvent(event)
+    if err == nil {
+        return nil // Success
+    }
+
+    // 4. Check if it's a conflict
+    if !errors.Is(err, aether.ErrVersionConflict) {
+        return err // Some other error
+    }
+
+    // 5. Implement your retry strategy
+    time.Sleep(yourBackoff(attempt))
+}
+```
+
+## Choosing a Pattern
+
+| Pattern | Latency | Throughput | Complexity | Use Case |
+|---------|---------|-----------|-----------|----------|
+| Simple | Low | Low | Very Low | Single writer, testing |
+| DetailedConflict | Low | Medium | Medium | Debugging, monitoring |
+| Jitter | Low-Medium | High | Low | Multi-writer concurrency |
+| Adaptive | Low-Medium | High | Medium | Variable load scenarios |
+| EventualConsistency | Very Low | Very High | High | High-volume, async-OK workloads |
+| CircuitBreaker | Variable | Stable | High | Distributed, failure-resilient systems |
+
+## Performance Considerations
+
+1. **Backoff timing**: Shorter backoffs waste CPU on retries, longer backoffs increase latency
+2. **Retry limits**: Too few retries give up too early, too many waste resources
+3. **Jitter**: Essential for preventing synchronized retries in high-concurrency scenarios
+4. **Monitoring**: Track retry rates and conflict patterns to detect system issues
+
+## Testing
+
+Use `aether.NewInMemoryEventStore()` in tests:
+
+```go
+store := store.NewInMemoryEventStore()
+err := SimpleRetryPattern(store, "test-actor", "TestEvent")
+if err != nil {
+    t.Fatalf("retry pattern failed: %v", err)
+}
+```

examples/retry_patterns.go

@@ -0,0 +1,353 @@
+package examples
+
+import (
+	"errors"
+	"fmt"
+	"log"
+	"math"
+	"math/rand"
+	"time"
+
+	"git.flowmade.one/flowmade-one/aether"
+)
+
+// SimpleRetryPattern demonstrates a basic retry loop using VersionConflictError.
+//
+// This pattern is suitable for scenarios where you want to automatically retry
+// with exponential backoff when version conflicts occur.
+func SimpleRetryPattern(store aether.EventStore, actorID string, eventType string) error {
+	const maxRetries = 3
+	const initialBackoff = 100 * time.Millisecond
+
+	var event *aether.Event
+
+	for attempt := 0; attempt < maxRetries; attempt++ {
+		if attempt > 0 {
+			backoff := time.Duration(math.Pow(2, float64(attempt-1))) * initialBackoff
+			log.Printf("Retry attempt %d after %v", attempt, backoff)
+			time.Sleep(backoff)
+		}
+
+		// Get the current version for the actor
+		currentVersion, err := store.GetLatestVersion(actorID)
+		if err != nil {
+			return fmt.Errorf("failed to get latest version: %w", err)
+		}
+
+		// Create event with next version
+		event = &aether.Event{
+			ID:        fmt.Sprintf("evt-%d-%d", time.Now().UnixNano(), attempt),
+			EventType: eventType,
+			ActorID:   actorID,
+			Version:   currentVersion + 1,
+			Data:      map[string]interface{}{"attempt": attempt},
+			Timestamp: time.Now(),
+		}
+
+		// Attempt to save
+		if err := store.SaveEvent(event); err == nil {
+			log.Printf("Successfully saved event for actor %s at version %d", actorID, event.Version)
+			return nil
+		} else if !errors.Is(err, aether.ErrVersionConflict) {
+			// Some other error occurred
+			return fmt.Errorf("save event failed: %w", err)
+		}
+		// If it's a version conflict, loop will retry
+	}
+
+	return fmt.Errorf("failed to save event after %d retries", maxRetries)
+}
+
+// ConflictDetailedRetryPattern demonstrates how to extract detailed information
+// from VersionConflictError to make intelligent retry decisions.
+//
+// This pattern shows how to log detailed context and potentially implement
+// circuit-breaker logic based on the conflict information.
+func ConflictDetailedRetryPattern(store aether.EventStore, actorID string, eventType string) error {
+	const maxRetries = 5
+	var lastConflictVersion int64
+
+	for attempt := 0; attempt < maxRetries; attempt++ {
+		// Get current version
+		currentVersion, err := store.GetLatestVersion(actorID)
+		if err != nil {
+			return err
+		}
+
+		// Create event
+		event := &aether.Event{
+			ID:        fmt.Sprintf("evt-%s-%d", actorID, time.Now().UnixNano()),
+			EventType: eventType,
+			ActorID:   actorID,
+			Version:   currentVersion + 1,
+			Data:      map[string]interface{}{"timestamp": time.Now()},
+			Timestamp: time.Now(),
+		}
+
+		// Attempt to save
+		err = store.SaveEvent(event)
+		if err == nil {
+			return nil // Success
+		}
+
+		// Check if it's a version conflict
+		var versionErr *aether.VersionConflictError
+		if !errors.As(err, &versionErr) {
+			// Not a version conflict, fail immediately
+			return err
+		}
+
+		// Extract detailed context from the conflict error
+		log.Printf(
+			"Version conflict for actor %q: attempted version %d, current version %d",
+			versionErr.ActorID,
+			versionErr.AttemptedVersion,
+			versionErr.CurrentVersion,
+		)
+
+		// Check for thrashing (multiple conflicts with same version)
+		if lastConflictVersion == versionErr.CurrentVersion && attempt > 0 {
+			log.Printf("Detected version thrashing - circuit breaker would trigger here")
+			return fmt.Errorf("circuit breaker: too many conflicts at version %d", versionErr.CurrentVersion)
+		}
+		lastConflictVersion = versionErr.CurrentVersion
+
+		// Exponential backoff
+		backoff := time.Duration(math.Pow(2, float64(attempt))) * 100 * time.Millisecond
+		time.Sleep(backoff)
+	}
+
+	return fmt.Errorf("failed after %d retries", maxRetries)
+}
+
+// JitterRetryPattern implements exponential backoff with jitter to prevent
+// thundering herd when multiple writers retry simultaneously.
+func JitterRetryPattern(store aether.EventStore, actorID string, eventType string) error {
+	const maxRetries = 3
+	const baseBackoff = 100 * time.Millisecond
+	const maxJitter = 0.1 // 10% jitter
+
+	for attempt := 0; attempt < maxRetries; attempt++ {
+		currentVersion, err := store.GetLatestVersion(actorID)
+		if err != nil {
+			return err
+		}
+
+		event := &aether.Event{
+			ID:        fmt.Sprintf("evt-%s-%d", actorID, time.Now().UnixNano()),
+			EventType: eventType,
+			ActorID:   actorID,
+			Version:   currentVersion + 1,
+			Data:      map[string]interface{}{},
+			Timestamp: time.Now(),
+		}
+
+		err = store.SaveEvent(event)
+		if err == nil {
+			return nil
+		}
+
+		if !errors.Is(err, aether.ErrVersionConflict) {
+			return err
+		}
+
+		// Exponential backoff with jitter
+		exponentialBackoff := time.Duration(math.Pow(2, float64(attempt))) * baseBackoff
+		jitter := time.Duration(rand.Float64() * float64(exponentialBackoff) * maxJitter)
+		totalBackoff := exponentialBackoff + jitter
+
+		log.Printf("Retrying in %v (attempt %d/%d)", totalBackoff, attempt+1, maxRetries)
+		time.Sleep(totalBackoff)
+	}
+
+	return fmt.Errorf("failed after %d retries", maxRetries)
+}
+
+// AdaptiveRetryPattern adjusts retry strategy based on version conflict patterns.
+//
+// This pattern demonstrates how application logic can use CurrentVersion to
+// decide whether to retry, give up, or escalate to a higher-level handler.
+func AdaptiveRetryPattern(store aether.EventStore, actorID string, eventType string) error {
+	const maxRetries = 3
+
+	for attempt := 0; attempt < maxRetries; attempt++ {
+		currentVersion, err := store.GetLatestVersion(actorID)
+		if err != nil {
+			return err
+		}
+
+		event := &aether.Event{
+			ID:        fmt.Sprintf("evt-%s-%d", actorID, time.Now().UnixNano()),
+			EventType: eventType,
+			ActorID:   actorID,
+			Version:   currentVersion + 1,
+			Data:      map[string]interface{}{},
+			Timestamp: time.Now(),
+		}
+
+		err = store.SaveEvent(event)
+		if err == nil {
+			return nil
+		}
+
+		var versionErr *aether.VersionConflictError
+		if !errors.As(err, &versionErr) {
+			return err
+		}
+
+		// Adaptive backoff based on version distance
+		versionDistance := versionErr.CurrentVersion - versionErr.AttemptedVersion
+		if versionDistance > 10 {
+			// Many concurrent writers - back off more aggressively
+			log.Printf("High contention detected (gap: %d), aggressive backoff", versionDistance)
+			time.Sleep(time.Duration(versionDistance*10) * time.Millisecond)
+		} else if versionDistance > 3 {
+			// Moderate contention - normal backoff
+			log.Printf("Moderate contention detected (gap: %d)", versionDistance)
+			time.Sleep(time.Duration(versionDistance) * time.Millisecond)
+		} else {
+			// Light contention - minimal backoff
+			log.Printf("Light contention detected")
+			time.Sleep(50 * time.Millisecond)
+		}
+	}
+
+	return fmt.Errorf("failed after %d retries", maxRetries)
+}
+
+// EventualConsistencyPattern demonstrates how to handle version conflicts
+// in an eventually consistent manner by publishing to a retry queue.
+//
+// This is useful when immediate retry is not feasible, and you want to
+// defer the operation to a background worker.
+type RetryQueueItem struct {
+	Event              *aether.Event
+	ConflictVersion    int64
+	ConflictAttempted  int64
+	NextRetryTime      time.Time
+	FailureCount       int
+}
+
+func EventualConsistencyPattern(store aether.EventStore, retryQueue chan<- RetryQueueItem, event *aether.Event) {
+	err := store.SaveEvent(event)
+	if err == nil {
+		return
+	}
+
+	var versionErr *aether.VersionConflictError
+	if !errors.As(err, &versionErr) {
+		log.Printf("Non-retryable error: %v", err)
+		return
+	}
+
+	// Queue for retry - background worker will process this
+	retryItem := RetryQueueItem{
+		Event:             event,
+		ConflictVersion:   versionErr.CurrentVersion,
+		ConflictAttempted: versionErr.AttemptedVersion,
+		NextRetryTime:     time.Now().Add(1 * time.Second),
+		FailureCount:      0,
+	}
+
+	select {
+	case retryQueue <- retryItem:
+		log.Printf("Queued event for retry: actor=%s", event.ActorID)
+	case <-time.After(5 * time.Second):
+		log.Printf("Failed to queue event for retry (queue full)")
+	}
+}
+
+// CircuitBreakerPattern implements a simple circuit breaker for version conflicts.
+//
+// The circuit breaker tracks failure rates and temporarily stops retrying
+// when the failure rate gets too high, allowing the system to recover.
+type CircuitBreaker struct {
+	failureCount      int
+	successCount      int
+	state             string // "closed", "open", "half-open"
+	lastFailureTime   time.Time
+	openDuration      time.Duration
+	failureThreshold  int
+	successThreshold  int
+}
+
+func NewCircuitBreaker() *CircuitBreaker {
+	return &CircuitBreaker{
+		state:            "closed",
+		openDuration:     30 * time.Second,
+		failureThreshold: 5,
+		successThreshold: 3,
+	}
+}
+
+func (cb *CircuitBreaker) RecordSuccess() {
+	if cb.state == "half-open" {
+		cb.successCount++
+		if cb.successCount >= cb.successThreshold {
+			cb.state = "closed"
+			cb.failureCount = 0
+			cb.successCount = 0
+			log.Printf("Circuit breaker closed")
+		}
+	}
+}
+
+func (cb *CircuitBreaker) RecordFailure() {
+	cb.lastFailureTime = time.Now()
+	cb.failureCount++
+	if cb.failureCount >= cb.failureThreshold {
+		cb.state = "open"
+		log.Printf("Circuit breaker opened")
+	}
+}
+
+func (cb *CircuitBreaker) CanRetry() bool {
+	if cb.state == "closed" {
+		return true
+	}
+	if cb.state == "open" {
+		if time.Since(cb.lastFailureTime) > cb.openDuration {
+			cb.state = "half-open"
+			cb.failureCount = 0
+			cb.successCount = 0
+			log.Printf("Circuit breaker half-open")
+			return true
+		}
+		return false
+	}
+	// half-open state allows retries
+	return true
+}
+
+func CircuitBreakerRetryPattern(store aether.EventStore, cb *CircuitBreaker, actorID string, eventType string) error {
+	if !cb.CanRetry() {
+		return fmt.Errorf("circuit breaker open - not retrying")
+	}
+
+	currentVersion, err := store.GetLatestVersion(actorID)
+	if err != nil {
+		return err
+	}
+
+	event := &aether.Event{
+		ID:        fmt.Sprintf("evt-%s-%d", actorID, time.Now().UnixNano()),
+		EventType: eventType,
+		ActorID:   actorID,
+		Version:   currentVersion + 1,
+		Data:      map[string]interface{}{},
+		Timestamp: time.Now(),
+	}
+
+	err = store.SaveEvent(event)
+	if err == nil {
+		cb.RecordSuccess()
+		return nil
+	}
+
+	if !errors.Is(err, aether.ErrVersionConflict) {
+		return err
+	}
+
+	cb.RecordFailure()
+	return fmt.Errorf("save failed with version conflict, circuit breaker status: %s", cb.state)
+}

store/immutability_test.go

@@ -0,0 +1,215 @@
+package store
+
+import (
+	"testing"
+	"time"
+
+	"git.flowmade.one/flowmade-one/aether"
+)
+
+// TestEventImmutability_MemoryStore verifies that events cannot be modified after persistence
+// in the in-memory event store. This demonstrates the append-only nature of event sourcing.
+func TestEventImmutability_MemoryStore(t *testing.T) {
+	store := NewInMemoryEventStore()
+	actorID := "test-actor-123"
+
+	// Create and save an event
+	originalEvent := &aether.Event{
+		ID:        "evt-immutable-1",
+		EventType: "TestEvent",
+		ActorID:   actorID,
+		Version:   1,
+		Data: map[string]interface{}{
+			"value": "original",
+		},
+		Timestamp: time.Now(),
+	}
+
+	err := store.SaveEvent(originalEvent)
+	if err != nil {
+		t.Fatalf("SaveEvent failed: %v", err)
+	}
+
+	// Retrieve the event from the store
+	events, err := store.GetEvents(actorID, 0)
+	if err != nil {
+		t.Fatalf("GetEvents failed: %v", err)
+	}
+
+	if len(events) == 0 {
+		t.Fatal("expected 1 event, got 0")
+	}
+
+	retrievedEvent := events[0]
+
+	// Verify the stored event has the correct values
+	if retrievedEvent.Data["value"] != "original" {
+		t.Errorf("Data value mismatch: got %v, want %v", retrievedEvent.Data["value"], "original")
+	}
+
+	if retrievedEvent.EventType != "TestEvent" {
+		t.Errorf("EventType mismatch: got %q, want %q", retrievedEvent.EventType, "TestEvent")
+	}
+
+	// Verify ID is correct
+	if retrievedEvent.ID != "evt-immutable-1" {
+		t.Errorf("Event ID mismatch: got %q, want %q", retrievedEvent.ID, "evt-immutable-1")
+	}
+}
+
+// TestEventImmutability_NoUpdateMethod verifies that the EventStore interface
+// has only append, read methods - no Update or Delete methods.
+func TestEventImmutability_NoUpdateMethod(t *testing.T) {
+	// This test documents that the EventStore interface is append-only.
+	// The interface intentionally provides:
+	// - SaveEvent: append only
+	// - GetEvents: read only
+	// - GetLatestVersion: read only
+	//
+	// To verify this, we demonstrate that any attempt to call non-existent
+	// update/delete methods would be caught at compile time (not runtime).
+	// This is enforced by the interface definition in event.go which does
+	// not include Update, Delete, or Modify methods.
+
+	store := NewInMemoryEventStore()
+
+	// Compile-time check: these would not compile if we tried them:
+	// store.Update(event) // compile error: no such method
+	// store.Delete(eventID) // compile error: no such method
+	// store.Modify(eventID, newData) // compile error: no such method
+
+	// Only these methods exist:
+	var eventStore aether.EventStore = store
+	if eventStore == nil {
+		t.Fatal("eventStore is nil")
+	}
+	// If we got here, the compile-time checks passed
+	t.Log("EventStore interface enforces append-only semantics by design")
+}
+
+// TestEventImmutability_VersionOnlyGoesUp verifies that versions are monotonically
+// increasing and attempting to save with a non-increasing version fails.
+func TestEventImmutability_VersionOnlyGoesUp(t *testing.T) {
+	store := NewInMemoryEventStore()
+	actorID := "actor-version-check"
+
+	// Save first event with version 1
+	event1 := &aether.Event{
+		ID:        "evt-v1",
+		EventType: "Event1",
+		ActorID:   actorID,
+		Version:   1,
+		Data:      map[string]interface{}{},
+		Timestamp: time.Now(),
+	}
+
+	err := store.SaveEvent(event1)
+	if err != nil {
+		t.Fatalf("SaveEvent(v1) failed: %v", err)
+	}
+
+	// Try to save with same version - should fail
+	event2Same := &aether.Event{
+		ID:        "evt-v1-again",
+		EventType: "Event2",
+		ActorID:   actorID,
+		Version:   1, // Same version
+		Data:      map[string]interface{}{},
+		Timestamp: time.Now(),
+	}
+
+	err = store.SaveEvent(event2Same)
+	if err == nil {
+		t.Error("expected SaveEvent(same version) to fail, but it succeeded")
+	}
+
+	// Try to save with lower version - should fail
+	event3Lower := &aether.Event{
+		ID:        "evt-v0",
+		EventType: "Event3",
+		ActorID:   actorID,
+		Version:   0, // Lower version
+		Data:      map[string]interface{}{},
+		Timestamp: time.Now(),
+	}
+
+	err = store.SaveEvent(event3Lower)
+	if err == nil {
+		t.Error("expected SaveEvent(lower version) to fail, but it succeeded")
+	}
+
+	// Save with next version - should succeed
+	event4Next := &aether.Event{
+		ID:        "evt-v2",
+		EventType: "Event4",
+		ActorID:   actorID,
+		Version:   2,
+		Data:      map[string]interface{}{},
+		Timestamp: time.Now(),
+	}
+
+	err = store.SaveEvent(event4Next)
+	if err != nil {
+		t.Fatalf("SaveEvent(v2) failed: %v", err)
+	}
+
+	// Verify we have exactly 2 events
+	events, err := store.GetEvents(actorID, 0)
+	if err != nil {
+		t.Fatalf("GetEvents failed: %v", err)
+	}
+
+	if len(events) != 2 {
+		t.Errorf("expected 2 events, got %d", len(events))
+	}
+}
+
+// TestEventImmutability_EventCannotBeDeleted verifies that there is no way to delete
+// events from the store through the EventStore interface.
+func TestEventImmutability_EventCannotBeDeleted(t *testing.T) {
+	store := NewInMemoryEventStore()
+	actorID := "actor-nodelete"
+
+	// Save an event
+	event := &aether.Event{
+		ID:        "evt-nodelete",
+		EventType: "ImportantEvent",
+		ActorID:   actorID,
+		Version:   1,
+		Data:      map[string]interface{}{"critical": true},
+		Timestamp: time.Now(),
+	}
+
+	err := store.SaveEvent(event)
+	if err != nil {
+		t.Fatalf("SaveEvent failed: %v", err)
+	}
+
+	// Retrieve it
+	events1, err := store.GetEvents(actorID, 0)
+	if err != nil {
+		t.Fatalf("GetEvents (1) failed: %v", err)
+	}
+
+	if len(events1) != 1 {
+		t.Fatal("expected 1 event after save")
+	}
+
+	// Try to delete through interface - this method doesn't exist
+	// store.Delete("evt-nodelete") // compile error: no such method
+	// store.DeleteByActorID(actorID) // compile error: no such method
+
+	// Verify the event is still there (we can't delete it)
+	events2, err := store.GetEvents(actorID, 0)
+	if err != nil {
+		t.Fatalf("GetEvents (2) failed: %v", err)
+	}
+
+	if len(events2) != 1 {
+		t.Errorf("expected 1 event (should not be deletable), got %d", len(events2))
+	}
+
+	if events2[0].ID != "evt-nodelete" {
+		t.Errorf("event ID changed: got %q, want %q", events2[0].ID, "evt-nodelete")
+	}
+}

store/jetstream.go

@@ -9,6 +9,7 @@ import (
 
 	"git.flowmade.one/flowmade-one/aether"
 	"github.com/nats-io/nats.go"
+	"github.com/google/uuid"
 )
 
 // Default configuration values for JetStream event store
@@ -19,7 +20,14 @@ const (
 
 // JetStreamConfig holds configuration options for JetStreamEventStore
 type JetStreamConfig struct {
-	// StreamRetention is how long to keep events (default: 1 year)
+	// StreamRetention is how long to keep events (default: 1 year).
+	// JetStream enforces this retention policy at the storage level using a limits-based policy:
+	// - MaxAge: Events older than this duration are automatically deleted
+	// - Storage is file-based (nats.FileStorage) for durability
+	// - Once the retention period expires, events are permanently removed from the stream
+	// This ensures that old events do not consume storage indefinitely.
+	// To keep events indefinitely, set StreamRetention to a very large value or configure
+	// a custom retention policy in the JetStream stream configuration.
 	StreamRetention time.Duration
 	// ReplicaCount is the number of replicas for high availability (default: 1)
 	ReplicaCount int
@@ -41,6 +49,21 @@ func DefaultJetStreamConfig() JetStreamConfig {
 // JetStreamEventStore implements EventStore using NATS JetStream for persistence.
 // It also implements EventStoreWithErrors to report malformed events during replay.
 //
+// ## Immutability Guarantee
+//
+// JetStreamEventStore is append-only. Events are stored in a JetStream stream that
+// is configured with file-based storage (nats.FileStorage) and a retention policy
+// (nats.LimitsPolicy). The configured MaxAge retention policy ensures that old events
+// eventually expire, but during their lifetime, events are never modified or deleted
+// through the EventStore API. Once an event is published to the stream:
+// - It cannot be updated
+// - It cannot be deleted before expiration
+// - It can only be read
+//
+// This architectural guarantee, combined with the EventStore interface providing
+// no Update or Delete methods, ensures events are immutable and suitable as an
+// audit trail.
+//
 // ## Version Cache Invalidation Strategy
 //
 // JetStreamEventStore maintains an in-memory cache of actor versions for optimistic
@@ -64,17 +87,13 @@ type JetStreamEventStore struct {
 	config     JetStreamConfig
 	mu         sync.Mutex       // Protects version checks during SaveEvent
 	versions   map[string]int64 // actorID -> latest version cache
+	broadcaster aether.EventBroadcaster // Optional broadcaster for EventStored events
+	namespace   string              // Optional namespace for event publishing
 }
 
 
 
 
-
-
-
-
-
-
 // NewJetStreamEventStore creates a new JetStream-based event store with default configuration
 func NewJetStreamEventStore(natsConn *nats.Conn, streamName string) (*JetStreamEventStore, error) {
 	return NewJetStreamEventStoreWithConfig(natsConn, streamName, DefaultJetStreamConfig())
@@ -130,6 +149,8 @@ func NewJetStreamEventStoreWithConfig(natsConn *nats.Conn, streamName string, co
 		streamName: effectiveStreamName,
 		config:     config,
 		versions:   make(map[string]int64),
+		broadcaster: nil,
+		namespace:   "",
 	}, nil
 }
 
@@ -143,6 +164,58 @@ func (jes *JetStreamEventStore) GetStreamName() string {
 	return jes.streamName
 }
 
+// NewJetStreamEventStoreWithBroadcaster creates a new JetStream-based event store with broadcaster support.
+// The broadcaster receives EventStored events when events are successfully saved.
+func NewJetStreamEventStoreWithBroadcaster(natsConn *nats.Conn, streamName string, broadcaster aether.EventBroadcaster, namespace string) (*JetStreamEventStore, error) {
+	config := DefaultJetStreamConfig()
+	if namespace != "" {
+		config.Namespace = namespace
+	}
+
+	js, err := natsConn.JetStream()
+	if err != nil {
+		return nil, fmt.Errorf("failed to get JetStream context: %w", err)
+	}
+
+	// Apply defaults for zero values
+	if config.StreamRetention == 0 {
+		config.StreamRetention = DefaultStreamRetention
+	}
+	if config.ReplicaCount == 0 {
+		config.ReplicaCount = DefaultReplicaCount
+	}
+
+	// Apply namespace prefix to stream name if provided
+	effectiveStreamName := streamName
+	if config.Namespace != "" {
+		effectiveStreamName = fmt.Sprintf("%s_%s", sanitizeSubject(config.Namespace), streamName)
+	}
+
+	// Create or update the stream
+	stream := &nats.StreamConfig{
+		Name:      effectiveStreamName,
+		Subjects:  []string{fmt.Sprintf("%s.events.>", effectiveStreamName), fmt.Sprintf("%s.snapshots.>", effectiveStreamName)},
+		Storage:   nats.FileStorage,
+		Retention: nats.LimitsPolicy,
+		MaxAge:    config.StreamRetention,
+		Replicas:  config.ReplicaCount,
+	}
+
+	_, err = js.AddStream(stream)
+	if err != nil && !strings.Contains(err.Error(), "already exists") {
+		return nil, fmt.Errorf("failed to create stream: %w", err)
+	}
+
+	return &JetStreamEventStore{
+		js:          js,
+		streamName:  effectiveStreamName,
+		config:      config,
+		versions:    make(map[string]int64),
+		broadcaster: broadcaster,
+		namespace:   namespace,
+	}, nil
+}
+
 // SaveEvent persists an event to JetStream.
 // Returns VersionConflictError if the event's version is not strictly greater
 // than the current latest version for the actor.
@@ -203,9 +276,34 @@ func (jes *JetStreamEventStore) SaveEvent(event *aether.Event) error {
 	// Update version cache after successful publish
 	jes.versions[event.ActorID] = event.Version
 
+	// Publish EventStored event after successful save (if broadcaster is configured)
+	if jes.broadcaster != nil {
+		jes.publishEventStored(event)
+	}
+
 	return nil
 }
 
+// publishEventStored publishes an EventStored event to the broadcaster.
+// This is called after a successful SaveEvent to notify subscribers.
+func (jes *JetStreamEventStore) publishEventStored(originalEvent *aether.Event) {
+	eventStored := &aether.Event{
+		ID:        uuid.New().String(),
+		EventType: aether.EventTypeEventStored,
+		ActorID:   originalEvent.ActorID, // EventStored is about the original actor
+		Version:   originalEvent.Version, // Preserve the version of the stored event
+		Data: map[string]interface{}{
+			"eventId":   originalEvent.ID,
+			"actorId":   originalEvent.ActorID,
+			"version":   originalEvent.Version,
+			"timestamp": originalEvent.Timestamp.Unix(),
+		},
+		Timestamp: time.Now(),
+	}
+
+	jes.broadcaster.Publish(jes.namespace, eventStored)
+}
+
 // GetEvents retrieves all events for an actor since a version.
 // Note: This method silently skips malformed events for backward compatibility.
 // Use GetEventsWithErrors to receive information about malformed events.

store/memory.go

@@ -2,15 +2,19 @@ package store
 
 import (
 	"sync"
+	"time"
 
 	"git.flowmade.one/flowmade-one/aether"
+	"github.com/google/uuid"
 )
 
 // InMemoryEventStore provides a simple in-memory event store for testing
 type InMemoryEventStore struct {
-	mu        sync.RWMutex
+	mu           sync.RWMutex
-	events    map[string][]*aether.Event         // actorID -> events
+	events       map[string][]*aether.Event         // actorID -> events
-	snapshots map[string][]*aether.ActorSnapshot // actorID -> snapshots (sorted by version)
+	snapshots    map[string][]*aether.ActorSnapshot // actorID -> snapshots (sorted by version)
+	broadcaster  aether.EventBroadcaster            // optional broadcaster for EventStored events
+	namespace    string                             // optional namespace for event publishing
 }
 
 // NewInMemoryEventStore creates a new in-memory event store
@@ -21,9 +25,21 @@ func NewInMemoryEventStore() *InMemoryEventStore {
 	}
 }
 
+// NewInMemoryEventStoreWithBroadcaster creates a new in-memory event store with an event broadcaster
+// The broadcaster receives EventStored events when events are successfully saved.
+func NewInMemoryEventStoreWithBroadcaster(broadcaster aether.EventBroadcaster, namespace string) *InMemoryEventStore {
+	return &InMemoryEventStore{
+		events:      make(map[string][]*aether.Event),
+		snapshots:   make(map[string][]*aether.ActorSnapshot),
+		broadcaster: broadcaster,
+		namespace:   namespace,
+	}
+}
+
 // SaveEvent saves an event to the in-memory store.
 // Returns VersionConflictError if the event's version is not strictly greater
 // than the current latest version for the actor.
+// If a broadcaster is configured, publishes an EventStored event on success.
 func (es *InMemoryEventStore) SaveEvent(event *aether.Event) error {
 	es.mu.Lock()
 	defer es.mu.Unlock()
@@ -51,9 +67,35 @@ func (es *InMemoryEventStore) SaveEvent(event *aether.Event) error {
 		es.events[event.ActorID] = make([]*aether.Event, 0)
 	}
 	es.events[event.ActorID] = append(es.events[event.ActorID], event)
+
+	// Publish EventStored event after successful save (if broadcaster is configured)
+	if es.broadcaster != nil {
+		es.publishEventStored(event)
+	}
+
 	return nil
 }
 
+// publishEventStored publishes an EventStored event to the broadcaster.
+// This is called after a successful SaveEvent to notify subscribers.
+func (es *InMemoryEventStore) publishEventStored(originalEvent *aether.Event) {
+	eventStored := &aether.Event{
+		ID:        uuid.New().String(),
+		EventType: aether.EventTypeEventStored,
+		ActorID:   originalEvent.ActorID, // EventStored is about the original actor
+		Version:   originalEvent.Version, // Preserve the version of the stored event
+		Data: map[string]interface{}{
+			"eventId":   originalEvent.ID,
+			"actorId":   originalEvent.ActorID,
+			"version":   originalEvent.Version,
+			"timestamp": originalEvent.Timestamp.Unix(),
+		},
+		Timestamp: time.Now(),
+	}
+
+	es.broadcaster.Publish(es.namespace, eventStored)
+}
+
 // GetEvents retrieves events for an actor from a specific version
 func (es *InMemoryEventStore) GetEvents(actorID string, fromVersion int64) ([]*aether.Event, error) {
 	es.mu.RLock()

store/memory_test.go

@@ -1905,3 +1905,181 @@ func TestSaveEvent_MetadataPreservedAcrossMultipleEvents(t *testing.T) {
 		}
 	}
 }
+
+// === EventStored Publishing Tests ===
+
+func TestSaveEvent_WithBroadcaster_PublishesEventStored(t *testing.T) {
+	// Create a mock broadcaster to capture published events
+	broadcaster := aether.NewEventBus()
+	store := NewInMemoryEventStoreWithBroadcaster(broadcaster, "test-namespace")
+
+	// Subscribe to EventStored events
+	ch := broadcaster.Subscribe("test-namespace")
+	defer broadcaster.Unsubscribe("test-namespace", ch)
+
+	event := &aether.Event{
+		ID:        "evt-123",
+		EventType: "OrderPlaced",
+		ActorID:   "order-456",
+		Version:   1,
+		Data: map[string]interface{}{
+			"total": 100.50,
+		},
+		Timestamp: time.Now(),
+	}
+
+	// Save event
+	err := store.SaveEvent(event)
+	if err != nil {
+		t.Fatalf("SaveEvent failed: %v", err)
+	}
+
+	// Check if EventStored was published
+	select {
+	case publishedEvent := <-ch:
+		if publishedEvent == nil {
+			t.Fatal("received nil event from broadcaster")
+		}
+		if publishedEvent.EventType != aether.EventTypeEventStored {
+			t.Errorf("expected EventType %q, got %q", aether.EventTypeEventStored, publishedEvent.EventType)
+		}
+		if publishedEvent.ActorID != "order-456" {
+			t.Errorf("expected ActorID %q, got %q", "order-456", publishedEvent.ActorID)
+		}
+		if publishedEvent.Version != 1 {
+			t.Errorf("expected Version 1, got %d", publishedEvent.Version)
+		}
+		// Check data contains original event info
+		if publishedEvent.Data["eventId"] != "evt-123" {
+			t.Errorf("expected eventId %q, got %q", "evt-123", publishedEvent.Data["eventId"])
+		}
+	case <-time.After(100 * time.Millisecond):
+		t.Fatal("timeout waiting for EventStored event")
+	}
+}
+
+func TestSaveEvent_VersionConflict_NoEventStored(t *testing.T) {
+	broadcaster := aether.NewEventBus()
+	store := NewInMemoryEventStoreWithBroadcaster(broadcaster, "test-namespace")
+
+	// Subscribe to EventStored events
+	ch := broadcaster.Subscribe("test-namespace")
+	defer broadcaster.Unsubscribe("test-namespace", ch)
+
+	// Save first event
+	event1 := &aether.Event{
+		ID:        "evt-1",
+		EventType: "OrderPlaced",
+		ActorID:   "order-456",
+		Version:   1,
+		Data:      map[string]interface{}{},
+		Timestamp: time.Now(),
+	}
+
+	err := store.SaveEvent(event1)
+	if err != nil {
+		t.Fatalf("SaveEvent(event1) failed: %v", err)
+	}
+
+	// Drain the first EventStored event
+	select {
+	case <-ch:
+	case <-time.After(100 * time.Millisecond):
+		t.Fatal("timeout waiting for first EventStored event")
+	}
+
+	// Try to save event with non-increasing version (should fail)
+	event2 := &aether.Event{
+		ID:        "evt-2",
+		EventType: "OrderPlaced",
+		ActorID:   "order-456",
+		Version:   1, // Same version, should conflict
+		Data:      map[string]interface{}{},
+		Timestamp: time.Now(),
+	}
+
+	err = store.SaveEvent(event2)
+	if !errors.Is(err, aether.ErrVersionConflict) {
+		t.Fatalf("expected ErrVersionConflict, got %v", err)
+	}
+
+	// Verify no EventStored event was published
+	select {
+	case <-ch:
+		t.Fatal("expected no EventStored event, but received one")
+	case <-time.After(50 * time.Millisecond):
+		// Expected - no event published
+	}
+}
+
+func TestSaveEvent_MultipleEvents_PublishesMultipleEventStored(t *testing.T) {
+	broadcaster := aether.NewEventBus()
+	store := NewInMemoryEventStoreWithBroadcaster(broadcaster, "test-namespace")
+
+	// Subscribe to EventStored events
+	ch := broadcaster.Subscribe("test-namespace")
+	defer broadcaster.Unsubscribe("test-namespace", ch)
+
+	// Save multiple events
+	for i := int64(1); i <= 3; i++ {
+		event := &aether.Event{
+			ID:        fmt.Sprintf("evt-%d", i),
+			EventType: "OrderPlaced",
+			ActorID:   "order-456",
+			Version:   i,
+			Data:      map[string]interface{}{},
+			Timestamp: time.Now(),
+		}
+
+		err := store.SaveEvent(event)
+		if err != nil {
+			t.Fatalf("SaveEvent failed: %v", err)
+		}
+	}
+
+	// Verify we received 3 EventStored events in order
+	for i := int64(1); i <= 3; i++ {
+		select {
+		case publishedEvent := <-ch:
+			if publishedEvent == nil {
+				t.Fatal("received nil event from broadcaster")
+			}
+			if publishedEvent.Version != i {
+				t.Errorf("expected Version %d, got %d", i, publishedEvent.Version)
+			}
+		case <-time.After(100 * time.Millisecond):
+			t.Fatalf("timeout waiting for EventStored event %d", i)
+		}
+	}
+}
+
+func TestSaveEvent_WithoutBroadcaster_NoPanic(t *testing.T) {
+	// Test that SaveEvent works without a broadcaster (nil broadcaster)
+	store := NewInMemoryEventStore()
+
+	event := &aether.Event{
+		ID:        "evt-123",
+		EventType: "OrderPlaced",
+		ActorID:   "order-456",
+		Version:   1,
+		Data: map[string]interface{}{
+			"total": 100.50,
+		},
+		Timestamp: time.Now(),
+	}
+
+	// This should not panic even though broadcaster is nil
+	err := store.SaveEvent(event)
+	if err != nil {
+		t.Fatalf("SaveEvent failed: %v", err)
+	}
+
+	// Verify event was saved
+	events, err := store.GetEvents("order-456", 0)
+	if err != nil {
+		t.Fatalf("GetEvents failed: %v", err)
+	}
+	if len(events) != 1 {
+		t.Fatalf("expected 1 event, got %d", len(events))
+	}
+}