Worked on the emscripten-core/emscripten repository to address a critical runtime integration issue affecting browser-based testing. Delivered a targeted bug fix by adding the missing $addOnExit library function, which allowed emrun_postjs.js to correctly retrieve browser output when EXIT_RUNTIME was set to zero. This patch eliminated a persistent runtime error, improving the reliability and user experience of Emrun for browser environments. Demonstrated strong debugging skills and careful patch management within a complex build system. Utilized Python for scripting and build automation, ensuring seamless integration with C/C++ components and maintaining robust workflows within the project's version control system.