feat(agent): add InvalidateBootstrapCache for IdentitySync file changes

ContextBuilder.InvalidateBootstrapCache allows IdentitySync to force
reload of bootstrap files when identity docs change on disk.

pkg/agent/context.go

@@ -404,6 +404,14 @@ func (cb *ContextBuilder) cachedBootstrapFiles() string {
 	return cb.bootstrapCache
 }
 
+// InvalidateBootstrapCache forces the next BuildSystemPrompt to reload
+// bootstrap files from the delegate. Called by IdentitySync when files change.
+func (cb *ContextBuilder) InvalidateBootstrapCache() {
+	cb.cacheMu.Lock()
+	cb.bootstrapCache = ""
+	cb.cacheMu.Unlock()
+}
+
 func (cb *ContextBuilder) LoadBootstrapFiles() string {
 	if cb.delegate == nil {
 		return ""

pkg/sync/identity.go

@@ -49,6 +49,10 @@ type IdentitySync struct {
 	agentID     string
 	store       DocumentStore
 
+	// OnChange is called after CheckAndSync detects and persists file changes.
+	// Use it to invalidate downstream caches (e.g., bootstrap prompt cache).
+	OnChange func()
+
 	watcher  *fsnotify.Watcher
 	cancel   context.CancelFunc
 	wg       sync.WaitGroup
@@ -128,6 +132,9 @@ func (s *IdentitySync) CheckAndSync(ctx context.Context) error {
 		now := time.Now()
 		s.lastSync.Store(now.UnixNano())
 		_ = s.store.UpsertKV(ctx, s.agentID, kvLastSyncKey, now.Format(time.RFC3339Nano))
+		if s.OnChange != nil {
+			s.OnChange()
+		}
 	}
 	return nil
 }