macOS Apple Silicon (arm64): traffic light window controls clipped at bottom

Bug description

On Apple Silicon (M2, arm64) builds of Codex App, the three traffic light window controls (red/yellow/green) in the top-left corner are clipped at the bottom — the lower arc of each button is cut off, making them look like flattened semicircles instead of full circles.

This is visible immediately after opening the app, no interaction needed. Earlier Codex versions on this same machine did not have this issue — it regressed in recent updates.

Steps to reproduce

1. Install Codex App on any Apple Silicon Mac
2. Launch the app
3. Look at the top-left window controls

Expected behavior

Red, yellow, and green traffic light buttons should render as full circles with no clipping.

Actual behavior

The bottom ~3/4 of each button's lower arc is clipped, showing only the top portion.

Environment

• Codex App: 26.616.32156 (build 4157)
• Bundle ID: com.openai.codex
• Architecture: arm64
• macOS: 13.7.6 Ventura (22H625)
• Machine: Mac mini M2 (Mac14,3), 16 GB

Additional context

• Also reported on Intel in #27344 — this is the same symptom on arm64
• Regressed between earlier builds and build 4157
• Issue persists across app restarts