Regression: File diff expand/collapse control is missing in chat

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

26.527.31326 (3390)

What subscription do you have?

Pro

What platform is your computer?

Darwin 25.4.0 arm64 arm

What issue are you seeing?

<img width="754" height="163" alt="Image" src="https://github.com/user-attachments/assets/7437501f-4ea1-42fb-8d37-9df679362ae3" />

Before the latest update, there was an up/down arrow button to expand or collapse the diff for each file within the chat. That action now seems to be missing.

What steps can reproduce the bug?

1. Open a chat containing code changes with diffs across multiple files.
2. Find a file diff in the chat.
3. Look for the up/down arrow button to expand or collapse that file’s diff.
4. Notice that the button/action is no longer available.

What is the expected behavior?

_No response_

Additional information

_No response_