/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_

Start by reproducing the issue with Copilot CLI 1.0.27: keep uncommitted changes, begin another change, and invoke `/undo` while it is compiling. Inspect the `/undo` flow and verify that completion preserves earlier uncommitted changes while reverting only the latest change.

索引モデルが issue の本文から書いたものです。