Worked on the ClickHouse and Blargian/ClickHouse repositories, focusing on backend development and system programming using C++ and Python. Over two months, delivered features to improve error handling and diagnostics for shell command write operations and user-defined functions. Enhanced diagnostic clarity by introducing and later refining error codes to distinguish between shell command and internal file write errors, and improved exception reporting for UDF execution failures. Applied code formatting and style improvements for better maintainability without altering behavior. Addressed a bug by reverting an error code change to restore correct error semantics, demonstrating careful attention to integration testing and debugging.