Worked on the apple/swift-system repository to enhance Windows portability and data integrity in file I/O operations using Swift. Addressed a critical bug by implementing validation logic that checks buffer sizes against the DWORD_MAX (4GB) limit in Windows-specific pread and pwrite functions, preventing silent truncation and potential data corruption. Expanded automated test coverage to ensure that oversized buffers are properly rejected, reinforcing the reliability of cross-platform file operations. Applied expertise in error handling, system programming, and unit testing to deliver and verify the fix through two targeted commits, contributing to more robust and predictable file I/O behavior on Windows systems.