v1.6.21

本次新增 Eino 临时错误自动重试机制：遇 429、5xx、网络抖动等可恢复错误时，在保持同一会话上下文的前提下分段退避续跑（可配置次数与退避上限），不向模型注入重试说明；并保证重试时仍携带本轮用户输入，避免续跑后偏离当前问题。

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This release adds automatic retry for transient Eino run errors (429, 5xx, network issues, etc.): the handler persists trace, applies exponential backoff, and resumes within the same session without injecting retry notices into the model context. The current user message is preserved across retries so the agent stays aligned with the latest request.