Codex Desktop Markdown tab becomes unclosable after editing from source view

Bug report

Reproduction

1. Open a Markdown file in Codex Desktop and show its rendered Markdown preview in the right panel.
2. Switch the preview to show Markdown source.
3. Have Codex edit the Markdown file.
4. Observe the Markdown panel.

Actual behavior

The panel becomes stuck showing the diff. Toggling the preview does not restore the normal view, and the tab cannot be closed.

Comparison

If the Markdown preview is still in rendered-preview mode when the edit happens, the panel may show the diff, but cycling hide/show restores it. The unclosable state specifically occurs after switching to source view before the edit.

Expected behavior

After the edit, the Markdown tab should either show the updated source/preview or a closable diff view. The tab should remain closable in all cases.

Environment

• Codex Desktop version: 26.715.61943
• macOS: 15.7.8 (24G817)

This appears distinct from a Markdown diff rendering issue because the failure is a stuck, unclosable tab after the source-view transition.