Agents window: Focusing chat input resets resized chat panel width

### Type of issue

Bug

### Steps to reproduce

1. Open the Agents window in the single-detail-panel layout.
2. Resize the chat panel to be narrower, making the detail panel wider.
3. Focus elsewhere.
4. Focus the chat input again.

### Expected behavior

The chat panel keeps the narrower width set by the user, and the detail panel remains wider.

### Actual behavior

Focusing the chat input makes the chat panel return to a larger width, undoing the user's manual resize.