Worked on reliability improvements for the microsoft/libHttpClient repository by addressing a critical race condition in callback dispatch between the dispatch thread and the threadpool. Used C++ and concurrency techniques to implement a test hook and synchronization barrier, enabling deterministic reproduction of the issue and validation of the fix across continuous integration runs. This targeted change reduced the risk of delayed callback stalls, improving end-to-end request handling for client applications. The solution included the addition of the VerifyDelayedCallbackTimerRaceOnManualQueue test hook, which simulates precise interleaving scenarios, and strengthened unit testing coverage for concurrency edge cases, decreasing production risk and improving reliability.