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线上实测:reviewer 用 fable-5 报「There's an issue with the selected model (claude-fable-5)」(该档未对当前账号开通),但 isModelError 未命中此措辞 → 不回退 → 复审失败(verdict=null)。补正则后 fable-5 不可用会自动回退 opus 重试,复审正常。 Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>