code: func (f *folder) startWatch() {
  	ctx, cancel := context.WithCancel(f.ctx)
  	f.watchMut.Lock()
  	f.watchChan = make(chan []string)
  	f.watchCancel = cancel
  	f.watchMut.Unlock()
  	go f.startWatchAsync(ctx)
  }
docs: // startWatch should only ever be called synchronously. If you want to use
  // this asynchronously, you should probably use scheduleWatchRestart instead.