Guard page preprocessing for non-HTTP exceptions

Problem/Motivation

Rivet’s rivet_preprocess_page() assumes the request exception attribute always provides getStatusCode(). Drupal can provide an EnforcedResponseException, which does not implement that method. This causes a fatal error and blank HTTP 500 response during Entity Browser/AJAX response rendering.

Steps to reproduce

• Use Rivet 1.1.3 with Drupal 10.6.x.
• Render an Entity Browser response using the public theme.
• Select an existing entity and submit the selection.

The response fails with:

Call to undefined method Drupal\Core\Form\EnforcedResponseException::getStatusCode()
Expected: Non-HTTP exceptions should not cause theme preprocessing to fatal.

Proposed resolution

use Symfony\Component\HttpKernel\Exception\HttpExceptionInterface;

$status_code = $status instanceof HttpExceptionInterface
  ? $status->getStatusCode()
  : 0;

Remaining tasks

User interface changes

API changes

Data model changes