code: func (s *Server) Start(ctx context.Context) error {
  	s.mu.Lock()
  	defer s.mu.Unlock()
  
  	if s.cancelAll != nil {
  		return errAlreadyRunning
  	}
  
  	s.pctx, s.cancelAll = context.WithCancel(ctx)
  	return nil
  }
docs: // Start starts the watch server.