Merge main and address review feedback

- Add mutex protection to SaveSnapshot and GetLatestSnapshot
- Add nil validation in SaveSnapshot
- Fix key collision in TestSnapshotDataIntegrity_LargeState (use fmt.Sprintf)
- Add concurrent access tests for snapshots

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

store/memory.go

@@ -1,11 +1,15 @@
 package store
 
 import (
+	"fmt"
+	"sync"
+
 	"git.flowmade.one/flowmade-one/aether"
 )
 
 // InMemoryEventStore provides a simple in-memory event store for testing
 type InMemoryEventStore struct {
+	mu        sync.RWMutex
 	events    map[string][]*aether.Event         // actorID -> events
 	snapshots map[string][]*aether.ActorSnapshot // actorID -> snapshots (sorted by version)
 }
@@ -20,6 +24,9 @@ func NewInMemoryEventStore() *InMemoryEventStore {
 
 // SaveEvent saves an event to the in-memory store
 func (es *InMemoryEventStore) SaveEvent(event *aether.Event) error {
+	es.mu.Lock()
+	defer es.mu.Unlock()
+
 	if _, exists := es.events[event.ActorID]; !exists {
 		es.events[event.ActorID] = make([]*aether.Event, 0)
 	}
@@ -29,6 +36,9 @@ func (es *InMemoryEventStore) SaveEvent(event *aether.Event) error {
 
 // GetEvents retrieves events for an actor from a specific version
 func (es *InMemoryEventStore) GetEvents(actorID string, fromVersion int64) ([]*aether.Event, error) {
+	es.mu.RLock()
+	defer es.mu.RUnlock()
+
 	events, exists := es.events[actorID]
 	if !exists {
 		return []*aether.Event{}, nil
@@ -46,6 +56,9 @@ func (es *InMemoryEventStore) GetEvents(actorID string, fromVersion int64) ([]*a
 
 // GetLatestVersion returns the latest version for an actor
 func (es *InMemoryEventStore) GetLatestVersion(actorID string) (int64, error) {
+	es.mu.RLock()
+	defer es.mu.RUnlock()
+
 	events, exists := es.events[actorID]
 	if !exists || len(events) == 0 {
 		return 0, nil
@@ -63,6 +76,13 @@ func (es *InMemoryEventStore) GetLatestVersion(actorID string) (int64, error) {
 
 // SaveSnapshot saves a snapshot to the in-memory store
 func (es *InMemoryEventStore) SaveSnapshot(snapshot *aether.ActorSnapshot) error {
+	if snapshot == nil {
+		return fmt.Errorf("snapshot cannot be nil")
+	}
+
+	es.mu.Lock()
+	defer es.mu.Unlock()
+
 	if _, exists := es.snapshots[snapshot.ActorID]; !exists {
 		es.snapshots[snapshot.ActorID] = make([]*aether.ActorSnapshot, 0)
 	}
@@ -72,6 +92,9 @@ func (es *InMemoryEventStore) SaveSnapshot(snapshot *aether.ActorSnapshot) error
 
 // GetLatestSnapshot returns the most recent snapshot for an actor
 func (es *InMemoryEventStore) GetLatestSnapshot(actorID string) (*aether.ActorSnapshot, error) {
+	es.mu.RLock()
+	defer es.mu.RUnlock()
+
 	snapshots, exists := es.snapshots[actorID]
 	if !exists || len(snapshots) == 0 {
 		return nil, nil