code: func (s *Storage) BlobrefStrings() []string {
  	s.mu.RLock()
  	defer s.mu.RUnlock()
  	sorted := make([]string, 0, len(s.m))
  	for br := range s.m {
  		sorted = append(sorted, br.String())
  	}
  	sort.Strings(sorted)
  	return sorted
  }
docs: // BlobrefStrings returns the sorted stringified blobrefs stored in s.