[Desktop App] Sidebar overflows onto secondary monitor with mixed display scaling

What version of the Codex App are you using (From “About Codex” dialog)?

26.803.81509

What subscription do you have?

no

What platform is your computer?

Microsoft Windows NT 10.0.26200.0 x64

What issue are you seeing?

Summary

When using an external monitor with a laptop, if the Codex desktop app is maximized/fullscreen on the laptop's built-in display, part of the left sidebar overflows beyond the edge of the laptop display and appears on the external monitor.

This issue occurs in a multi-monitor setup where the two displays use different scaling settings.

Steps to Reproduce

1. Connect an external monitor to a laptop.
2. Configure Windows to use the laptop display and the external monitor as extended displays.
3. Set the display configuration as follows:

• Laptop built-in display: 2560 × 1600, 150% scaling
• External monitor: 2560 × 1440, 100% scaling

1. Open the Codex desktop app on the laptop's built-in display.
2. Maximize the Codex app.
3. Observe the left edge of the application near the boundary between the two displays.

Expected Behavior

The Codex app, including the left sidebar, should be fully contained within the boundaries of the display where the application window is located.

No part of the sidebar should render or overflow onto the external monitor.

Actual Behavior

Part of the left sidebar extends beyond the boundary of the laptop's display and appears on the external monitor.

A narrow portion of the Codex sidebar is visible on the second monitor, as shown in the attached screenshot.

Display Configuration

| Display | Resolution | Scaling |
| --- | --- | --- |
| Laptop built-in display | 2560 × 1600 | 150% |
| External monitor | 2560 × 1440 | 100% |

Environment

• OS: Windows
• Codex App Version: 26.803.81509
• Display mode: Extended displays
• Multi-monitor setup: Laptop built-in display + external monitor
• Mixed display scaling: Yes (150% and 100%)
• Codex window: Maximized on the laptop display

Screenshot

Attached below.

Additional Context

This may be related to mixed-DPI or multi-monitor display boundary calculations.

<img width="99" height="1440" alt="Image" src="https://github.com/user-attachments/assets/14072204-61a5-47ff-87f7-5cebef83bd1d" />

What steps can reproduce the bug?

When a laptop is connected to an external monitor, and the resolution of the laptop differs from or is the same as that of the external monitor, the left sidebar of the Codex application, when in full-screen mode on the laptop screen, overflows onto the external monitor.

<img width="99" height="1440" alt="Image" src="https://github.com/user-attachments/assets/394af565-7ab3-4110-855a-df465c99cefd" />

What is the expected behavior?

When the codex application is running on the laptop screen, whether it's in full-screen mode or not, it should only occupy the current screen in full-screen or non-full-screen mode, and should not overflow to the second screen.

Additional information

_No response_