Why are $_Files and/or HTTPFoundationFileBag invalid in custom module Controller?

I have noticed a very strange issue with accessing an individual file from the $_FILES object or the Symfony derived SymfonyComponentHTTPFoundationFileBag from within a custom module controller.

The exact location of the issue seems to be in SymfonyComponentHttpKernelHttpKernel -> handleRaw

Specifically, the file exists prior dispatching the KernelEvent::REQUEST but it does not after.

// request
$event = new GetResponseEvent($this, $request, $type);

// THE FILE EXISTS HERE
// file_exists( $request->files->get(0)->getRealPath()) == TRUE

$this->dispatcher->dispatch(KernelEvents::REQUEST, $event);

// THE FILE DOES NOT EXISTS HERE
// file_exists( $request->files->get(0)->getRealPath()) == FALSE

Here is the entire method for reference also including some code to move the file, which works as expected as long as it is before the event dispatch.

  /**
 * Handles a request to convert it to a response.
 *
 * Exceptions are not caught.
 *
 * @param Request $request A Request instance
 * @param int     $type    The type of the request (one of HttpKernelInterface::MASTER_REQUEST or HttpKernelInterface::SUB_REQUEST)
 *
 * @return Response A Response instance
 *
 * @throws LogicException       If one of the listener does not behave as expected
 * @throws NotFoundHttpException When controller cannot be found
 */
private function handleRaw(Request $request, $type = self::MASTER_REQUEST)
{
    $this->requestStack->push($request);


    $directory = Drupal::service('file_system')->realpath(file_default_scheme() . "://");

    /* @var SymfonyComponentHttpFoundationFileUploadedFile $uploadedFile*/
    $uploadedFile = $request->files->get(0);

    if (is_uploaded_file($uploadedFile->getRealPath())){
      $success = $uploadedFile->move($directory);
    }



  // request
    $event = new GetResponseEvent($this, $request, $type);
    $this->dispatcher->dispatch(KernelEvents::REQUEST, $event);

    if ($event->hasResponse()) {
        return $this->filterResponse($event->getResponse(), $request, $type);
    }

    // load controller
    if (false === $controller = $this->resolver->getController($request)) {
        throw new NotFoundHttpException(sprintf('Unable to find the controller for path "%s". The route is wrongly configured.', $request->getPathInfo()));
    }

    $event = new FilterControllerEvent($this, $controller, $request, $type);
    $this->dispatcher->dispatch(KernelEvents::CONTROLLER, $event);
    $controller = $event->getController();

    // controller arguments
    $arguments = $this->argumentResolver->getArguments($request, $controller);

    $event = new FilterControllerArgumentsEvent($this, $controller, $arguments, $request, $type);
    $this->dispatcher->dispatch(KernelEvents::CONTROLLER_ARGUMENTS, $event);
    $controller = $event->getController();
    $arguments = $event->getArguments();

    // call controller
    $response = call_user_func_array($controller, $arguments);

    // view
    if (!$response instanceof Response) {
        $event = new GetResponseForControllerResultEvent($this, $request, $type, $response);
        $this->dispatcher->dispatch(KernelEvents::VIEW, $event);

        if ($event->hasResponse()) {
            $response = $event->getResponse();
        }

        if (!$response instanceof Response) {
            $msg = sprintf('The controller must return a response (%s given).', $this->varToString($response));

            // the user may have forgotten to return something
            if (null === $response) {
                $msg .= ' Did you forget to add a return statement somewhere in your controller?';
            }
            throw new LogicException($msg);
        }
    }

    return $this->filterResponse($response, $request, $type);
}

I am trying to write a custom GraphQL module mutation plugin that handles file uploads and unless I can get access to the file object from the POST request, I don’t think this will be possible.

Any thoughts are greatly appreciated.

I believe this may be a core issue or an upstream issue with Symfony or at the very least a side effect of the assumptions of how new requests are created.

https://www.drupal.org/project/drupal/issues/2934486#comment-12406531