update all is_reserved templates each time

CRM/Upgrade/Form.php

@@ -581,6 +581,13 @@ public static function buildQueue($currentVer, $latestVer, $postUpgradeMessageFi
       $queue->createItem($task, ['weight' => 0]);
     }
 
+    $task = new CRM_Queue_Task(
+      ['CRM_Upgrade_Incremental_MessageTemplates', 'updateReservedTemplates'],
+      [$latestVer],
+      "Update all reserved message templates"
+    );
+    $queue->createItem($task, ['weight' => 990]);
+
     $task = new CRM_Queue_Task(
       ['CRM_Upgrade_Form', 'doCoreFinish'],
       [$rev, $latestVer, $latestVer, $postUpgradeMessageFile],

CRM/Upgrade/Incremental/MessageTemplates.php

@@ -487,6 +487,38 @@ public function getUpgradeMessages() {
     return $messages;
   }
 
+  /**
+   * Make sure *all* reserved ones got updated. Might be inefficient because we either already updated or
+   * there were no changes to a given template, but there's only about 30.
+   * Note this has to come after the is_default in-use templates are checked to see if they're different
+   * from the is_reserved version, otherwise that check can't tell which ones the site has changed.
+   *
+   * @param CRM_Queue_TaskContext $ctx
+   * @param string $version
+   * @return bool
+   */
+  public static function updateReservedTemplates(CRM_Queue_TaskContext $ctx, $version) {
+    if (version_compare($version, '5.26', '<')) {
+      // We can't do this before workflow_name was introduced. Strictly speaking we don't care until 5.54.
+      return TRUE;
+    }
+    $dao = CRM_Core_DAO::executeQuery("SELECT id, workflow_name FROM civicrm_msg_template WHERE is_reserved=1");
+    while ($dao->fetch()) {
+      foreach (['html', 'text', 'subject'] as $type) {
+        $content = file_get_contents(\Civi::paths()->getPath('[civicrm.root]/xml/templates/message_templates/' . $dao->workflow_name . '_' . $type . '.tpl'));
+        if ($content) {
+          CRM_Core_DAO::executeQuery(
+            "UPDATE civicrm_msg_template SET msg_{$type} = %1 WHERE id = %2", [
+              1 => [$content, 'String'],
+              2 => [$dao->id, 'Integer'],
+            ]
+          );
+        }
+      }
+    }
+    return TRUE;
+  }
+
   /**
    * Update message templates.
    */