Undo failed in latest extension (26.513)

What version of the IDE extension are you using?

26.513.21555

What subscription do you have?

Plus

Which IDE are you using?

vs code

What platform is your computer?

Windows 11 x64

What issue are you seeing?

<img width="1866" height="633" alt="Image" src="https://github.com/user-attachments/assets/999d888f-8518-4bcf-b746-8c871b69a3e1" />

As shown in the image, I have already made sure that git status is clean, but even the simplest changes still fail to undo.
The issue also occurs in the Codex app, not just in the VS Code extension.

What steps can reproduce the bug?

Editing any file causes the same problem. I’m not able to get any additional error details.

What is the expected behavior?

_No response_

Additional information

<img width="1131" height="342" alt="Image" src="https://github.com/user-attachments/assets/2c178b2b-66bf-40de-a80e-8b8f7943117e" />

It said "Failed to load the complete file contents." when viewing the changes