Function apply_task_update 

fn apply_task_update(
    current_task: &mut Option<TaskState>,
    update: TaskState,
    can_finish: bool,
) -> bool

Apply only progress fields from the model. The user-owned goal is immutable within the standing task; steering is appended by the harness above. The model may refine the default success criterion once, but cannot erase or replace an established criterion. Completion is accepted only at a harness safe point with no new or in-flight execution.