Function parse_internal_attribute 

pub fn parse_internal_attribute<'a>(
    model_name: &str,
    raw: &'a str,
) -> Result<&'a str, String>

Parses one @@internal("action") attribute’s action name and validates it against INTERNAL_ACTIONS. Returns Err naming the model and the bad action for anything else — the compile-error case the design’s acceptance criteria requires (“@@internal naming an action that is not a valid action verb ⇒ compile error naming the model and the bad action”).