/undo undid too much in a file

### Describe the bug

I was in the process of working on something with copilot CLI, had some uncommitted changes and then asked for another change. That last change didn't actually make sense, so I used `/undo` while the change was still executing (I think it was compiling). The state of the conversation reverted correctly, but the state of the file didn't: it reverted to no uncommitted changes.

I was able to restore the changes by telling copilot about it.

### Affected version

1.0.27

### Steps to reproduce the behavior

_No response_

### Expected behavior

_No response_

### Additional context

_No response_

先使用 Copilot CLI 1.0.27 重現問題：保留未提交的變更，開始另一項變更，並在其進行編譯時呼叫 `/undo`。檢查 `/undo` 流程，並確認完成後會保留先前未提交的變更，而只復原最新的變更。

由索引模型根據 Issue 內容生成。