Sergey contributed to the curl/curl repository by addressing a build configuration issue related to the SHA-512/256 hash option. He identified and corrected the order of option() and mark_as_advanced() calls within CMakeLists.txt, ensuring that the SHA-512/256 algorithm option is properly recognized and configured across different platforms. This targeted fix, implemented using CMake and C/C++, improved build reliability and reduced the risk of misconfiguration-related failures. Sergey’s work demonstrated a focused approach to build-system debugging and patching, delivering a precise solution that enhances cross-platform consistency and reduces support overhead for developers relying on accurate cryptographic option wiring.