PageUp/PageDown in focused composer horizontally shifts and breaks VS Code chat webview layout

What version of the IDE extension are you using?

26.506.31421

What subscription do you have?

plus

Which IDE are you using?

vs code

What platform is your computer?

Microsoft Windows NT 10.0.26100.0 x64

What issue are you seeing?

When a Codex thread is open and the composer input has focus, pressing PageUp or PageDown horizontally scrolls/shifts the entire webview. After that, the Codex UI is clipped on the left, controls and content are misaligned, and a horizontal scrollbar appears at the bottom of the webview.

This is unexpected because while the text input/composer is focused, PageUp / PageDown should be handled by the input/editor caret behavior. It should not scroll the surrounding webview or change the panel layout.

https://github.com/user-attachments/assets/90ea6ecd-5b72-4024-b51b-417675b97ea6

<img width="1395" height="1230" alt="Image" src="https://github.com/user-attachments/assets/2ed03239-60f3-4d79-969d-9935b649d172" />

What steps can reproduce the bug?

1. Open VS Code on Windows.
2. Open the Codex extension side panel / secondary side bar.
3. Open an existing Codex thread or start a new one.
4. Click into the composer input at the bottom and type some text, leaving keyboard focus in the composer.
5. Press PageUp or PageDown.

Observed: the entire Codex webview shifts horizontally; content is clipped on the left and a horizontal scrollbar appears at the bottom.

Expected: since the composer is focused, PageUp / PageDown should affect only the composer caret/selection behavior, not scroll or shift the surrounding webview.

What is the expected behavior?

_No response_

Additional information

_No response_