Use `AgentSettings::get_layout(cx)` to retrieve the current, exact value of the user's layout settings, and `AgentSettings::set_layout(WindowLayout::agent())` or `AgentSettings::set_layout(cached_user_settings)` to write to them.

Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Closes #ISSUE

Release Notes:

- N/A