Worked on the bytedance/deer-flow repository to deliver a secure file upload feature for Windows, focusing on mitigating TOCTOU vulnerabilities through dual lstat checks and fstat validation. Applied Python and backend development skills to implement symlink protection, ensuring uploads are handled safely across platforms. Enhanced the project’s reliability by expanding and updating tests for cross-platform compatibility and translating comments to improve maintainability and onboarding. Prioritized security hardening and documentation updates, positioning the codebase for release readiness. The work emphasized thorough testing and validation, resulting in improved code quality and reduced risk around file uploads, particularly in Windows environments.