After an approved plan is implemented by the agent, if I want to add somethin...

After an approved plan is implemented by the agent, if I want to add something more to the plan in the same session, the plan description doesn't get updated, only the to-do list gets updated unless I manually tell it to do so. Please fix this to update the plan description before I can check and approve it again.

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| Field | Value |
| --- | --- |
| App version | 1.1.10 |
| OS | Windows 10.0.26200 |
| Theme | GitHub |
| Path | /chat |
| Tenure | Week 11 |

从 /chat 流程开始，重现已批准的计划在同一会话中收到额外工作的情况。检查计划描述和待办事项列表在批准前是如何更新的。在用户能够再次查看并批准计划之前，描述已反映新增的工作，即视为完成；验证现有的待办事项列表更新行为仍然保持不变。

由索引模型根据 Issue 内容生成。