code: func (b *Butler) Streams() []types.StreamName {
  	var streams types.StreamNameSlice
  	func() {
  		b.streamSeenLock.Lock()
  		defer b.streamSeenLock.Unlock()
  
  		streams = make([]types.StreamName, 0, b.streamSeen.Len())
  		b.streamSeen.Iter(func(s string) bool {
  			streams = append(streams, types.StreamName(s))
  			return true
  		})
  	}()
  
  	sort.Sort(streams)
  	return ([]types.StreamName)(streams)
  }
docs: // Streams returns a sorted list of stream names that have been registered to
  // the Butler.