Henry Tai developed a MacOS Screen Brightness Library for the facebook/buck2-prelude repository, focusing on cross-platform display management. He implemented both hardware-level brightness control using DDC and software-based adjustments via gamma tables, addressing the needs of external and built-in Mac displays. By leveraging private APIs, Henry ensured comprehensive support for end-to-end brightness management, integrating these capabilities into a reusable library module for future Buck2 tooling enhancements. His work involved system programming and framework integration, primarily using Bzl, and demonstrated a deep understanding of macOS development. The project delivered a robust foundation for further display-related features within the Buck2 ecosystem.