Scott Cao focused on stabilizing build automation for the facebook/buck2-prelude repository by addressing regressions in Rust toolchain integration. He reverted changes that had disrupted RunInfo support for rustc and rustdoc, as well as the argument handling in redirect_stdout.py, restoring reliable script behavior. Using Python and Starlark, Scott validated the stability of these tools across both CI and local environments, ensuring consistent build outcomes. His work reinforced the reliability of the build system and scripting infrastructure, reducing the risk of toolchain regressions. This targeted bug fix demonstrated a deep understanding of build systems and the nuances of Rust toolchain workflows.