Diffs in markdown are rendered as the entire file

What version of the Codex App are you using (From “About Codex” dialog)?

26.305.950 (863)

What subscription do you have?

Plus

What platform is your computer?

Darwin 25.1.0 arm64 arm

What issue are you seeing?

When rendering preview for diffs, codes will automatically render the entire MD file as MD, which sounds like a good idea, but I can't see the actual diff easily 🤔

<img width="1449" height="689" alt="Image" src="https://github.com/user-attachments/assets/0faecb55-1082-44f7-8d99-525411b8b1c9" />

What steps can reproduce the bug?

1. Tell codex to edit any MD file
2. look at diff
3. see entire MD file without any diffs shown

What is the expected behavior?

1. Tell codex to edit any MD file
2. look at diff
3. see diff (or 2 rendered MD files side by side / or inline "diff" colors in rendered MD)

Additional information

_No response_