fix: enable hot reload for amp-model-mappings config

- Store ampModule in Server struct to access it during config updates
- Call ampModule.OnConfigUpdated() in UpdateClients() for hot reload
- Watch config directory instead of file to handle atomic saves (vim, VSCode, etc.)
- Improve config file event detection with basename matching
- Add diagnostic logging for config reload tracing

internal/api/modules/amp/amp.go

@@ -166,7 +166,10 @@ func (m *AmpModule) getAuthMiddleware(ctx modules.Context) gin.HandlerFunc {
 func (m *AmpModule) OnConfigUpdated(cfg *config.Config) error {
 	// Update model mappings (hot-reload supported)
 	if m.modelMapper != nil {
+		log.Infof("amp config updated: reloading %d model mapping(s)", len(cfg.AmpModelMappings))
 		m.modelMapper.UpdateMappings(cfg.AmpModelMappings)
+	} else {
+		log.Warnf("amp model mapper not initialized, skipping model mapping update")
 	}
 
 	if !m.enabled {

internal/api/server.go

@@ -150,6 +150,9 @@ type Server struct {
 	// management handler
 	mgmt *managementHandlers.Handler
 
+	// ampModule is the Amp routing module for model mapping hot-reload
+	ampModule *ampmodule.AmpModule
+
 	// managementRoutesRegistered tracks whether the management routes have been attached to the engine.
 	managementRoutesRegistered atomic.Bool
 	// managementRoutesEnabled controls whether management endpoints serve real handlers.
@@ -268,14 +271,14 @@ func NewServer(cfg *config.Config, authManager *auth.Manager, accessManager *sdk
 	s.setupRoutes()
 
 	// Register Amp module using V2 interface with Context
-	ampModule := ampmodule.NewLegacy(accessManager, AuthMiddleware(accessManager))
+	s.ampModule = ampmodule.NewLegacy(accessManager, AuthMiddleware(accessManager))
 	ctx := modules.Context{
 		Engine:         engine,
 		BaseHandler:    s.handlers,
 		Config:         cfg,
 		AuthMiddleware: AuthMiddleware(accessManager),
 	}
-	if err := modules.RegisterModule(ctx, ampModule); err != nil {
+	if err := modules.RegisterModule(ctx, s.ampModule); err != nil {
 		log.Errorf("Failed to register Amp module: %v", err)
 	}
 
@@ -916,6 +919,16 @@ func (s *Server) UpdateClients(cfg *config.Config) {
 		s.mgmt.SetAuthManager(s.handlers.AuthManager)
 	}
 
+	// Notify Amp module of config changes (for model mapping hot-reload)
+	if s.ampModule != nil {
+		log.Debugf("triggering amp module config update")
+		if err := s.ampModule.OnConfigUpdated(cfg); err != nil {
+			log.Errorf("failed to update Amp module config: %v", err)
+		}
+	} else {
+		log.Warnf("amp module is nil, skipping config update")
+	}
+
 	// Count client sources from configuration and auth directory
 	authFiles := util.CountAuthFiles(cfg.AuthDir)
 	geminiAPIKeyCount := len(cfg.GeminiKey)

internal/watcher/watcher.go

@@ -162,12 +162,14 @@ func NewWatcher(configPath, authDir string, reloadCallback func(*config.Config))
 
 // Start begins watching the configuration file and authentication directory
 func (w *Watcher) Start(ctx context.Context) error {
-	// Watch the config file
+	// Watch the config file's parent directory instead of the file itself.
-	if errAddConfig := w.watcher.Add(w.configPath); errAddConfig != nil {
+	// This handles editors that use atomic save (write to temp, then rename).
-		log.Errorf("failed to watch config file %s: %v", w.configPath, errAddConfig)
+	configDir := filepath.Dir(w.configPath)
+	if errAddConfig := w.watcher.Add(configDir); errAddConfig != nil {
+		log.Errorf("failed to watch config directory %s: %v", configDir, errAddConfig)
 		return errAddConfig
 	}
-	log.Debugf("watching config file: %s", w.configPath)
+	log.Debugf("watching config directory: %s (for file: %s)", configDir, filepath.Base(w.configPath))
 
 	// Watch the auth directory
 	if errAddAuthDir := w.watcher.Add(w.authDir); errAddAuthDir != nil {
@@ -700,7 +702,23 @@ func (w *Watcher) isKnownAuthFile(path string) bool {
 func (w *Watcher) handleEvent(event fsnotify.Event) {
 	// Filter only relevant events: config file or auth-dir JSON files.
 	configOps := fsnotify.Write | fsnotify.Create | fsnotify.Rename
-	isConfigEvent := event.Name == w.configPath && event.Op&configOps != 0
+	// Check if this event is for our config file (handle both exact match and basename match for directory watching)
+	isConfigEvent := false
+	if event.Op&configOps != 0 {
+		// Exact path match
+		if event.Name == w.configPath {
+			isConfigEvent = true
+		} else {
+			// Check if basename matches and it's in the config directory (for atomic save detection)
+			configDir := filepath.Dir(w.configPath)
+			configBase := filepath.Base(w.configPath)
+			eventDir := filepath.Dir(event.Name)
+			eventBase := filepath.Base(event.Name)
+			if eventDir == configDir && eventBase == configBase {
+				isConfigEvent = true
+			}
+		}
+	}
 	authOps := fsnotify.Create | fsnotify.Write | fsnotify.Remove | fsnotify.Rename
 	isAuthJSON := strings.HasPrefix(event.Name, w.authDir) && strings.HasSuffix(event.Name, ".json") && event.Op&authOps != 0
 	if !isConfigEvent && !isAuthJSON {