Ted Bowman
--- a/automatic_updates_extensions/src/Validator/ForbidCoreChangesValidator.php 0 → 100644
+++ b/automatic_updates_extensions/src/Validator/ForbidCoreChangesValidator.php 0 → 100644
+   * it ensures that the 'drupal/core' is included in the list if present.
+   *
+   * @param string $composer_root
+   *   The path to the composer root.
+   *
+   * @return \Drupal\package_manager\InstalledPackagesList
+   *   The installed core packages.
+   */
+  private function getInstalledCorePackages(string $composer_root): InstalledPackagesList {
+    $installed_package_list = $this->composerInspector->getInstalledPackagesList($composer_root);
+    $core_packages = $installed_package_list->getCorePackages();
+    if (isset($installed_package_list['drupal/core']) && !isset($core_packages['drupal/core'])) {
+      $core_packages = new InstalledPackagesList(array_merge($core_packages->getArrayCopy(), ['drupal/core' => $installed_package_list['drupal/core']]));
+    }
+    return $core_packages;
+  }
--- a/automatic_updates_extensions/src/Validator/ForbidCoreChangesValidator.php 0 → 100644
+++ b/automatic_updates_extensions/src/Validator/ForbidCoreChangesValidator.php 0 → 100644
+   * @param \Drupal\package_manager\Event\StatusCheckEvent|\Drupal\package_manager\Event\PreApplyEvent $event
+   *   The event object.
+   */
+  public function validateStagedCorePackages(StatusCheckEvent|PreApplyEvent $event): void {
+    $stage = $event->stage;
+    // We only want to do this check if the stage belongs to Automatic Updates
+    // Extensions.
+    if ($stage->getType() !== 'automatic_updates_extensions:attended' || !$stage->stageDirectoryExists()) {
+      return;
+    }
+    $active_core_packages = $this->getInstalledCorePackages($this->pathLocator->getProjectRoot());
+    $stage_core_packages = $this->getInstalledCorePackages($stage->getStageDirectory());
+
+    $new_packages = $stage_core_packages->getPackagesNotIn($active_core_packages);
+    $removed_packages = $active_core_packages->getPackagesNotIn($stage_core_packages);
+    $changed_packages = $active_core_packages->getPackagesWithDifferentVersionsIn($stage_core_packages);