docs: @Override
    protected void onResponseImpl(InnerT response) {
      IllegalStateException error = null;
  
      // Guard against unsolicited notifications
      if (!awaitingInner || !newItem.compareAndSet(null, response)) {
        // Notify downstream if it's still open
        error = new IllegalStateException("Received unsolicited response from upstream.");
        cancellation.compareAndSet(null, error);
      }
      deliver();
  
      // Notify upstream by throwing an exception
      if (error != null) {
        throw error;
      }
    }