Worked on stabilizing the ONNX build system by addressing a regression related to protobuf integration in the onnx/onnx repository. Focused on ensuring that protobuf is compiled only when ONNX_BUILD_CUSTOM_PROTOBUF is enabled and protoc is not predefined, resolving a conditional compilation bug that previously caused build failures. Utilized C++, CMake, and build system expertise to implement a targeted fix, which improved reliability across different environments and reduced CI failures. The solution enhanced traceability by referencing the relevant pull request, making future maintenance easier. Demonstrated a methodical approach to debugging and resolving complex build system issues within a collaborative workflow.