return ErrUnknownHandler
	}
	s := strings.Join(subroute, "/")
	if debugPrint {
		fmt.Println("RegisterSingleHandler: ", id.String(), "subroute:", s)
	}

	if len(subroute) == 0 {
		if m.handlers.hasAny(id) && !id.isTestHandler() {
			return fmt.Errorf("handler %v: %w", id.String(), ErrHandlerAlreadyExists)
		}

		m.handlers.single[id] = h
		return nil
	}
	subID := makeSubHandlerID(id, s)

func (h *handlers) init() {
	h.subSingle = make(map[subHandlerID]SingleHandlerFn)
	h.subStateless = make(map[subHandlerID]*StatelessHandler)
	h.subStreams = make(map[subHandlerID]*StreamHandler)
}

func (h *handlers) hasAny(id HandlerID) bool {
	if !id.valid() {
		return false
	}
	return h.single[id] != nil || h.stateless[id] != nil || h.streams[id] != nil
}

func (h *handlers) hasSubhandler(id subHandlerID) bool {