Codex Windows app maximized window leaks thin strip onto adjacent monitor

Summary

The Codex Windows desktop app leaks a thin vertical strip of its maximized window onto the adjacent monitor in a dual-monitor setup. Other Windows applications maximize correctly and stay within the selected monitor.

Environment

• Product: Codex desktop app on Windows
• OS: Windows 11
• Codex app version: 26.601.2237.0
• Display setup: dual-monitor display
• Date observed: 2026-06-03, Asia/Seoul timezone

Steps to reproduce

1. Use Windows 11 with a dual-monitor setup.
2. Open the Codex desktop app.
3. Move Codex to one monitor.
4. Maximize the Codex window using the normal window maximize control.
5. Observe that a thin vertical strip of the Codex window appears on the adjacent monitor.
6. Click the adjacent monitor.
7. Observe that the leaked strip briefly flickers/repaints.

Expected behavior

When maximized, the Codex window should remain fully contained within the selected monitor, like other Windows applications.

Actual behavior

A thin vertical strip of the Codex window extends onto the adjacent monitor. When focus changes by clicking the adjacent monitor, the strip briefly flickers/repaints; for a split second the desktop wallpaper appears, then the Codex strip appears again.

Additional details

• F11 fullscreen mode appears normal.
• The issue only occurs with the normal maximized window state.
• Other applications on the same system maximize correctly and do not cross the monitor boundary.

This looks like a maximized-window frame/bounds calculation issue specific to the Codex Windows desktop app rather than a general Windows display configuration problem.