code: func (q *pendingCallRegistry) WithReservedRequestID(ctx context.Context) (context.Context, int) {
  	q.mutex.Lock()
  	defer q.mutex.Unlock()
  	q.callIDSeq++
  	id := q.callIDSeq
  	newContext := context.WithValue(ctx, reservedRequestIDKey{}, id)
  	return newContext, id
  }
docs: // Creates a new context that contains a reserved JSON RPC protocol level request id.
  // It can be for instance be useful when the request id used for upcoming call needs to be known.