Open a session from a subfolder within a repo rather than root repo directory

I want to be able to open a session from a subfolder within a repo rather than only open it at the root directory of a repo

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| Field | Value |
| --- | --- |
| App version | 1.0.24 |
| OS | macOS 26.5.2 |
| Theme | Notionish |
| Path | /chat |
| Tenure | Week 4 |

该 issue 未指明文件、测试或入口点。首先追踪 app 在打开会话时如何选择 repository 根目录，然后确定可以在哪里保留所选的子文件夹。完成标准是：从 repository 子文件夹打开会话能够正常工作，同时现有的根目录行为保持不变。

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