anchor.diff:    Future addTag(String uuid, String name) {
       final completer = new Completer();
   
  +    // validate uuid
  +    if (!PinUtility.isUuid(uuid)) {
  +      PinLogger.instance.shout('[CartModel] addTag: uuid format invalid: ${uuid}}');
  +      completer.complete(null);
  +    }
  +
       int timestamp = PinTime.getTime();
   
       tags.addNewTag(uuid, name, timestamp: timestamp);
  
positive.code:   Future addCategory(String uuid, String name) {
      final completer = new Completer();
  
      var timestamp = PinTime.getTime();
  
      categories.addNewCategory(uuid, name, timestamp: timestamp);
  
negative.code:   }
  
    Future removePost(String uuid) {
      final completer = new Completer();
  
      // validate uuid
      if (!PinUtility.isUuid(uuid)) {
        PinLogger.instance.shout('[CartModel] removePost: uuid format invalid: ${uuid}}');
        completer.complete(null);
      }
    }
  
    Future _addPost(String uuid, String markdown, CartPostHeader header, String html) {
  