feat: implement cross-node event broadcasting with NATSEventBus

- Add UpdateVersionCache method to JetStreamEventStore for cache synchronization
- Add SubscribeToEventStored convenience helper to NATSEventBus
- Create integration tests for cross-node broadcasting scenarios
- Add example demonstrating NATSEventBus + JetStreamEventStore integration

store/integration_test.go

@@ -0,0 +1,420 @@
+//go:build integration
+// +build integration
+
+package store
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"testing"
+	"time"
+
+	"git.flowmade.one/flowmade-one/aether"
+	"github.com/nats-io/nats.go"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// generateStreamName creates a unique stream name for each test run
+func generateStreamName(baseName string) string {
+	return fmt.Sprintf("%s_%s_%d", baseName, "tv149", time.Now().UnixNano()%100000000)
+}
+
+// cleanupStream deletes a JetStream stream if it exists.
+func cleanupStream(nc *nats.Conn, streamName string) {
+	js, err := nc.JetStream()
+	if err != nil {
+		return
+	}
+	err = js.DeleteStream(streamName)
+	// Silently ignore errors - we just want to clean up
+	_ = err
+}
+
+// TestCrossNodeBroadcasting_SingleNode tests basic cross-node broadcasting
+// on a single node (local loopback).
+func TestCrossNodeBroadcasting_SingleNode(t *testing.T) {
+	nc, err := nats.Connect(nats.DefaultURL)
+	require.NoError(t, err)
+	defer nc.Close()
+
+	streamName := generateStreamName("broadcast_single")
+	cleanupStream(nc, streamName)
+
+	// Create NATS event bus
+	natsBus, err := aether.NewNATSEventBus(nc)
+	require.NoError(t, err)
+	defer natsBus.Stop()
+
+	// Create event store with broadcaster
+	store, err := NewJetStreamEventStoreWithBroadcaster(
+		nc,
+		streamName,
+		natsBus,
+		"tenant-single",
+	)
+	require.NoError(t, err)
+
+	// Subscribe to events
+	eventCh := natsBus.Subscribe("tenant-single")
+
+	// Save event
+	testEvent := &aether.Event{
+		ID:        "event-1",
+		EventType: "TestEvent",
+		ActorID:   "actor-1",
+		Version:   1,
+		Data:      map[string]interface{}{"test": "single"},
+		Timestamp: time.Now(),
+	}
+
+	err = store.SaveEvent(testEvent)
+	require.NoError(t, err)
+	log.Printf("Saved event: %s", testEvent.ID)
+
+	// Receive event via NATS (NATSBroadcast may have wrapped in EventStored)
+	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
+	defer cancel()
+
+	select {
+	case received := <-eventCh:
+		// The received event should have the same actor and version
+		assert.Equal(t, "actor-1", received.ActorID)
+		assert.Equal(t, int64(1), received.Version)
+		// Event type might be original or EventStored wrapper
+		if received.EventType == aether.EventTypeEventStored {
+			assert.Equal(t, "actor-1", received.Data["actorId"].(string))
+			log.Printf("Received EventStored wrapper: %s", received.ID)
+		} else {
+			log.Printf("Received via NATS: %s (type: %s)", received.ID, received.EventType)
+		}
+	case <-ctx.Done():
+		t.Fatal("Did not receive event via NATS")
+	}
+}
+
+// TestCrossNodeBroadcasting_MultiNode tests broadcasting between two nodes.
+func TestCrossNodeBroadcasting_MultiNode(t *testing.T) {
+	nc, err := nats.Connect(nats.DefaultURL)
+	require.NoError(t, err)
+	defer nc.Close()
+
+	streamName := generateStreamName("broadcast_multi")
+	cleanupStream(nc, streamName)
+
+	// Create Node A
+	nodeANatsBus, err := aether.NewNATSEventBus(nc)
+	require.NoError(t, err)
+	defer nodeANatsBus.Stop()
+
+	nodeAStore, err := NewJetStreamEventStoreWithBroadcaster(
+		nc,
+		streamName,
+		nodeANatsBus,
+		"tenant-multi",
+	)
+	require.NoError(t, err)
+
+	// Create Node B
+	nodeBNatsBus, err := aether.NewNATSEventBus(nc)
+	require.NoError(t, err)
+	defer nodeBNatsBus.Stop()
+
+	nodeBStore, err := NewJetStreamEventStoreWithBroadcaster(
+		nc,
+		streamName,
+		nodeBNatsBus,
+		"tenant-multi",
+	)
+	require.NoError(t, err)
+
+	// Node A subscribes
+	nodeAEventCh := nodeANatsBus.Subscribe("tenant-multi")
+
+	// Node B subscribes
+	nodeBEventCh := nodeBNatsBus.Subscribe("tenant-multi")
+
+	// Node A saves event
+	eventA := &aether.Event{
+		ID:        "event-node-a",
+		EventType: "TestEvent",
+		ActorID:   "multi-actor",
+		Version:   1,
+		Data:      map[string]interface{}{"node": "a"},
+		Timestamp: time.Now(),
+	}
+
+	err = nodeAStore.SaveEvent(eventA)
+	require.NoError(t, err)
+	log.Printf("Node A saved: %s", eventA.ID)
+
+	// Node B receives event (EventStored wrapper or original)
+	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
+	defer cancel()
+
+	select {
+	case received := <-nodeBEventCh:
+		// Check actor and version match
+		assert.Equal(t, "multi-actor", received.ActorID)
+		assert.Equal(t, int64(1), received.Version)
+		if received.EventType == aether.EventTypeEventStored {
+			// EventStored wrapper
+			assert.Equal(t, "multi-actor", received.Data["actorId"].(string))
+		} else {
+			// Original event
+			assert.Equal(t, "a", received.Data["node"])
+		}
+		log.Printf("Node B received: %s (actor: %s, version: %d)", received.ID, received.ActorID, received.Version)
+	case <-ctx.Done():
+		t.Fatal("Node B did not receive event")
+	}
+
+	// Give Node B time to receive and process Node A's event
+	time.Sleep(100 * time.Millisecond)
+
+	// Node B saves event with different actor
+	eventB := &aether.Event{
+		ID:        "event-node-b",
+		EventType: "TestEvent",
+		ActorID:   "multi-actor-b", // Different actor
+		Version:   1,
+		Data:      map[string]interface{}{"node": "b"},
+		Timestamp: time.Now(),
+	}
+
+	err = nodeBStore.SaveEvent(eventB)
+	require.NoError(t, err)
+	log.Printf("Node B saved: %s", eventB.ID)
+
+	// Node A receives Node B's event (could be EventStored or original)
+	ctx2, cancel2 := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel2()
+
+	// Wait for either EventStored or the actual event
+	received := false
+	for !received {
+		select {
+		case event := <-nodeAEventCh:
+			// Check for Node B's event
+			if event.EventType == aether.EventTypeEventStored {
+				// EventStored wrapper - check actorId
+				actorID := event.Data["actorId"].(string)
+				if actorID == "multi-actor-b" {
+					received = true
+					log.Printf("Node A received EventStored for Node B's event: %s", event.ID)
+				}
+			} else if event.ActorID == "multi-actor-b" {
+				received = true
+				log.Printf("Node A received Node B's event: %s", event.ID)
+			}
+			// Keep listening until we get Node B's event
+		case <-ctx2.Done():
+			if !received {
+				t.Fatal("Node A did not receive Node B's event")
+			}
+		}
+	}
+}
+
+// TestUpdateVersionCache tests the version cache update logic.
+func TestUpdateVersionCache(t *testing.T) {
+	nc, err := nats.Connect(nats.DefaultURL)
+	require.NoError(t, err)
+	defer nc.Close()
+
+	streamName := generateStreamName("cache_test")
+	cleanupStream(nc, streamName)
+
+	store, err := NewJetStreamEventStore(nc, streamName)
+	require.NoError(t, err)
+
+	// Save event version 1
+	event1 := &aether.Event{
+		ID:        "event-1",
+		EventType: "TestEvent",
+		ActorID:   "actor-1",
+		Version:   1,
+		Data:      map[string]interface{}{},
+		Timestamp: time.Now(),
+	}
+	err = store.SaveEvent(event1)
+	require.NoError(t, err)
+
+	// EventStored will trigger UpdateVersionCache
+	time.Sleep(100 * time.Millisecond)
+
+	// Save event version 2 - should succeed (version > 1)
+	event2 := &aether.Event{
+		ID:        "event-2",
+		EventType: "TestEvent",
+		ActorID:   "actor-1",
+		Version:   2,
+		Data:      map[string]interface{}{},
+		Timestamp: time.Now(),
+	}
+	err = store.SaveEvent(event2)
+	require.NoError(t, err)
+
+	// Save event version 3 - should succeed (version > 2)
+	event3 := &aether.Event{
+		ID:        "event-3",
+		EventType: "TestEvent",
+		ActorID:   "actor-1",
+		Version:   3,
+		Data:      map[string]interface{}{},
+		Timestamp: time.Now(),
+	}
+	err = store.SaveEvent(event3)
+	require.NoError(t, err)
+
+	// Verify all events can be retrieved
+	events, err := store.GetEvents("actor-1", 0)
+	require.NoError(t, err)
+	assert.Len(t, events, 3)
+
+	// Verify latest version
+	latest, err := store.GetLatestVersion("actor-1")
+	require.NoError(t, err)
+	assert.Equal(t, int64(3), latest)
+
+	// Manually update cache with version 5 (simulating external update)
+	store.UpdateVersionCache("actor-1", 5)
+
+	// Verify version 4 would conflict (4 < cached 5)
+	event4 := &aether.Event{
+		ID:        "event-4",
+		EventType: "TestEvent",
+		ActorID:   "actor-1",
+		Version:   4,
+		Data:      map[string]interface{}{},
+		Timestamp: time.Now(),
+	}
+	err = store.SaveEvent(event4)
+	assert.Error(t, err, "version 4 should conflict with cached version 5")
+
+	// Version 6 should succeed (6 > 5)
+	event6 := &aether.Event{
+		ID:        "event-6",
+		EventType: "TestEvent",
+		ActorID:   "actor-1",
+		Version:   6,
+		Data:      map[string]interface{}{},
+		Timestamp: time.Now(),
+	}
+	err = store.SaveEvent(event6)
+	require.NoError(t, err)
+
+	// Verify version 6 was saved
+	latest, err = store.GetLatestVersion("actor-1")
+	require.NoError(t, err)
+	assert.Equal(t, int64(6), latest)
+}
+
+// TestSubscribeToEventStored tests the convenience helper.
+func TestSubscribeToEventStored(t *testing.T) {
+	nc, err := nats.Connect(nats.DefaultURL)
+	require.NoError(t, err)
+	defer nc.Close()
+
+	natsBus, err := aether.NewNATSEventBus(nc)
+	require.NoError(t, err)
+	defer natsBus.Stop()
+
+	// Use helper
+	eventStoredCh := natsBus.SubscribeToEventStored("test-store")
+
+	// Verify channel is created
+	assert.NotNil(t, eventStoredCh)
+
+	// Publish EventStored manually (version will be float64 from JSON)
+	eventStored := &aether.Event{
+		ID:        "stored-1",
+		EventType: aether.EventTypeEventStored,
+		ActorID:   "actor-1",
+		Version:   1,
+		Data: map[string]interface{}{
+			"actorId": "actor-1",
+			"version": 1.0, // Use float64 to match JSON encoding
+		},
+		Timestamp: time.Now(),
+	}
+
+	natsBus.Publish("test-store", eventStored)
+
+	// Should receive the EventStored
+	ctx, cancel := context.WithTimeout(context.Background(), 500*time.Millisecond)
+	defer cancel()
+
+	select {
+	case received := <-eventStoredCh:
+		assert.Equal(t, aether.EventTypeEventStored, received.EventType)
+		assert.Equal(t, "actor-1", received.ActorID)
+		log.Printf("Received EventStored: %s", received.ID)
+	case <-ctx.Done():
+		t.Fatal("Did not receive EventStored")
+	}
+}
+
+// TestCrossNodeBroadcasting_NamespaceIsolation tests namespace isolation.
+func TestCrossNodeBroadcasting_NamespaceIsolation(t *testing.T) {
+	nc, err := nats.Connect(nats.DefaultURL)
+	require.NoError(t, err)
+	defer nc.Close()
+
+	streamName := generateStreamName("namespace_isolation")
+	cleanupStream(nc, streamName)
+
+	// Create stores with different namespaces
+	storeA, err := NewJetStreamEventStoreWithBroadcaster(
+		nc,
+		streamName,
+		nil,
+		"tenant-a",
+	)
+	require.NoError(t, err)
+
+	storeB, err := NewJetStreamEventStoreWithBroadcaster(
+		nc,
+		streamName,
+		nil,
+		"tenant-b",
+	)
+	require.NoError(t, err)
+
+	// Save to each namespace
+	eventA := &aether.Event{
+		ID:        "event-a",
+		EventType: "TestEvent",
+		ActorID:   "actor-a",
+		Version:   1,
+		Data:      map[string]interface{}{"tenant": "a"},
+		Timestamp: time.Now(),
+	}
+
+	err = storeA.SaveEvent(eventA)
+	require.NoError(t, err)
+
+	eventB := &aether.Event{
+		ID:        "event-b",
+		EventType: "TestEvent",
+		ActorID:   "actor-b",
+		Version:   1,
+		Data:      map[string]interface{}{"tenant": "b"},
+		Timestamp: time.Now(),
+	}
+
+	err = storeB.SaveEvent(eventB)
+	require.NoError(t, err)
+
+	// Verify each store can see its own events
+	eventsA, err := storeA.GetEvents("actor-a", 0)
+	require.NoError(t, err)
+	assert.Len(t, eventsA, 1)
+	assert.Equal(t, "a", eventsA[0].Data["tenant"])
+
+	eventsB, err := storeB.GetEvents("actor-b", 0)
+	require.NoError(t, err)
+	assert.Len(t, eventsB, 1)
+	assert.Equal(t, "b", eventsB[0].Data["tenant"])
+}