Developed a thread-safe NegativeCache for the leil-io/saunafs repository, enabling early negative responses and reducing latency for failed lookups in the sauna client and sfsmount. The solution featured configurable timeout and maximum size, using an LRU-like eviction strategy to manage cache entries efficiently. Integrated directly into the sauna_client lookup path, it returned immediate negative results and improved observability through enhanced logging. Comprehensive unit and system tests validated eviction logic, timeouts, and size constraints, while related mount lookup code was refactored for clarity and performance. The work leveraged C++, concurrency, and bash scripting to optimize reliability and maintainability.