code: func (s *fsStore) listManifests(transaction string) ([]string, error) {
  	transactionDir := filepath.Join(s.root, makeFilesafeName(transaction))
  	fileInfos, err := ioutil.ReadDir(transactionDir)
  	switch {
  	case os.IsNotExist(err):
  		return nil, nil
  	case err != nil:
  		return nil, err
  	}
  
  	filenames := []string{}
  	for _, info := range fileInfos {
  		filenames = append(filenames, info.Name())
  	}
  	return filenames, nil
  }
docs: // listManifests stored in a transaction