Payload:    req,
		DeadlineMS: uint32(m.deadline.Milliseconds()),
	}
	if m.subroute != nil {
		msg.Flags |= FlagSubroute
	}
	ch := make(chan Response, 1)
	m.respMu.Lock()
	if m.closed {
		m.respMu.Unlock()
		return nil, ErrDisconnected
	}
	m.respWait = ch
	m.respMu.Unlock()
	ctx := m.ctx

	// Add deadline if none.
	if msg.DeadlineMS == 0 {