In April 2026, Mizeyuyu developed a concurrency locking feature for sandboxed file operations in the bytedance/deer-flow repository. The work focused on backend development using Python, with an emphasis on concurrency management and threading. Mizeyuyu designed a locking mechanism that serializes operations on the same virtual path within isolated sandboxes, preventing data races and ensuring per-sandbox isolation by using a composite lock key. The locking logic was modularized into a standalone file for maintainability and reuse. Comprehensive regression tests were added to validate concurrent operations, demonstrating a thoughtful approach to correctness, isolation, and long-term code maintainability in multi-tenant environments.