fix(watcher): guard debounced callback after Stop

internal/watcher/watcher.go

@@ -6,6 +6,7 @@ import (
 	"context"
 	"strings"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	"github.com/fsnotify/fsnotify"
@@ -39,6 +40,7 @@ type Watcher struct {
 	serverUpdateTimer *time.Timer
 	serverUpdateLast  time.Time
 	serverUpdatePend  bool
+	stopped           atomic.Bool
 	reloadCallback    func(*config.Config)
 	watcher           *fsnotify.Watcher
 	lastAuthHashes    map[string]string
@@ -119,6 +121,7 @@ func (w *Watcher) Start(ctx context.Context) error {
 
 // Stop stops the file watcher
 func (w *Watcher) Stop() error {
+	w.stopped.Store(true)
 	w.stopDispatch()
 	w.stopConfigReloadTimer()
 	w.stopServerUpdateTimer()