Description: MacBook Air M5, using only built-in display. The login window renders full screen normally. After logging into desktop session, the display canvas gets cropped with a black bar on the bottom-right corner. This issue is reproducible in Safe Mode and with a brand-new admin user account. No third-party display or window management software installed. Suspected WindowServer display coordinate calculation bug within user session. Environment Device: MacBook Air M5 OS: macOS 27.2 RC (26B118) Display: Built-in display only, no external monitor Reproduction steps Boot to login window, display works fine Log into desktop session Display canvas cropped, black bar appears at bottom-right