During January 2026, d01c2 focused on enhancing the robustness of the tc39/test262 repository by improving test coverage for JavaScript core builtins. They addressed error propagation in String.fromCharCode, specifically targeting scenarios where ToNumber fails with BigInt inputs. Using JavaScript and testing methodologies, d01c2 developed targeted regression tests to validate that abrupt completions from ToNumber are correctly surfaced at the call site, aligning with ECMAScript specifications. This work deepened the reliability of test262’s coverage for ToNumber and ToUint16 error paths, supporting future bug fixes and ensuring that error handling in core builtins remains maintainable and spec-conformant.