code: func (b *EtcdBackend) NewWatcher(ctx context.Context, watch backend.Watch) (backend.Watcher, error) {
  	select {
  	case <-b.watchStarted.Done():
  	case <-ctx.Done():
  		return nil, trace.ConnectionProblem(ctx.Err(), "context is closing")
  	}
  	return b.buf.NewWatcher(ctx, watch)
  }
docs: // NewWatcher returns a new event watcher