code: func (ss *FileSubStore) AddSeqPending(subid, seqno uint64) error {
  	ss.Lock()
  	ss.updateSub.ID, ss.updateSub.Seqno = subid, seqno
  	if err := ss.writeRecord(nil, subRecMsg, &ss.updateSub); err != nil {
  		ss.Unlock()
  		return err
  	}
  	si := ss.subs[subid]
  	if si != nil {
  		s := si.(*subscription)
  		if seqno > s.sub.LastSent {
  			s.sub.LastSent = seqno
  		}
  		s.seqnos[seqno] = struct{}{}
  	}
  	ss.Unlock()
  	return nil
  }
docs: // AddSeqPending adds the given message seqno to the given subscription.