Worked on the gin-gonic/gin repository to address a regression in file upload handling, focusing on backend development with Go. Delivered a targeted bug fix in the SaveUploadedFile function to ensure that permission changes are only applied to newly created directories, preventing errors when saving uploads to system-owned paths such as /tmp. Developed a platform-agnostic regression test to validate this behavior across various environments, improving test reliability and reducing CI flakiness. The solution preserved existing permission semantics while maintaining compatibility with previous versions, demonstrating careful attention to cross-platform consistency and robust backend engineering practices using Go and automated testing.