code: func (h *handler) close(err error, inflightReq *requestOp) {
  	h.cancelAllRequests(err, inflightReq)
  	h.callWG.Wait()
  	h.cancelRoot()
  	h.cancelServerSubscriptions(err)
  }
docs: // close cancels all requests except for inflightReq and waits for
  // call goroutines to shut down.