code: func (m *metadataTracker) devices() []protocol.DeviceID {
  	devs := make(map[protocol.DeviceID]struct{}, len(m.counts.Counts))
  
  	m.mut.RLock()
  	for _, dev := range m.counts.Counts {
  		if dev.Sequence > 0 {
  			id := protocol.DeviceIDFromBytes(dev.DeviceID)
  			if id == protocol.GlobalDeviceID || id == protocol.LocalDeviceID {
  				continue
  			}
  			devs[id] = struct{}{}
  		}
  	}
  	m.mut.RUnlock()
  
  	devList := make([]protocol.DeviceID, 0, len(devs))
  	for dev := range devs {
  		devList = append(devList, dev)
  	}
  
  	return devList
  }
docs: // devices returns the list of devices tracked, excluding the local device
  // (which we don't know the ID of)