Worked on the flipt-io/flipt-client-sdks repository to address a critical concurrency issue affecting engine retrieval and evaluation stability. Using Rust, FFI, and WASM, updated the engine access pattern to return a shared reference rather than a mutable one, eliminating undefined behavior caused by cross-thread aliasing. This change ensured thread safety for evaluation operations across language boundaries. To validate the fix, introduced a regression test that exercises concurrent evaluation scenarios, confirming the solution’s effectiveness under multi-threaded conditions. The work improved the SDK’s reliability and maintainability, aligning its FFI and WASM evaluation paths with robust thread-safety guarantees for production environments.