Worked on the facebook/zstd repository to deliver a robust sparse-destination file workflow, focusing on improving how the system handles file opening and verification for sparse file support. Leveraged C programming and system programming skills to implement open-time checks that ensure destination files are properly validated, even when they do not exist beforehand. Enhanced error handling and expanded test coverage to address edge cases and failure scenarios, particularly around file descriptor management. Updated existing tests to reflect the new behavior, strengthening reliability for users working with sparse files. The work emphasized thorough testing and careful file I/O handling to improve overall stability.