BigPipeTestHooks.php

<?php

declare (strict_types=1);
namespace Drupal\big_pipe_test\Hook;

use Drupal\Core\Hook\Attribute\Hook;

/**
 * Hook implementations for big_pipe_test.
 */
class BigPipeTestHooks {
  
  /**
   * Implements hook_page_top().
   */
  public function pageTop(array &$page_top) : void {
    // Ensure this hook is invoked on every page load.
    $page_top['#cache']['max-age'] = 0;
    $request = \Drupal::request();
    if ($request->query
      ->get('trigger_session')) {
      $request->getSession()
        ->set('big_pipe_test', TRUE);
    }
  }

}