code: func (m *monitor) sync() error {
  	names, _, err := m.harvest("")
  	if len(names) > 0 {
  		m.tip = names
  	} else {
  		m.tip = defaultTip
  	}
  	return err
  }
docs: // sync fetches the current tip of a listing endpoint, so that grawbots crawling
  // forward in time don't treat it as a new post, or reprocess it when restarted.