Yufei Yuan focused on stabilizing and maintaining core build infrastructure for the facebook/folly and pytorch/pytorch repositories, addressing critical build and compatibility issues over a two-month period. He resolved multiple C++ variable shadowing bugs that blocked successful builds, notably in the ThreadPoolExecutor and RegexMatchCache components, by refactoring code to eliminate naming conflicts and ensure warning flags did not escalate to errors. Yufei also improved cross-compiler support by adjusting build system configurations, particularly separating Clang-specific flags to restore GCC compatibility. His work, primarily in C++, Bazel, and Python, enhanced CI reliability and streamlined onboarding for contributors by reducing build failures.