Worked on the NomicFoundation/hardhat repository to enhance the reliability of the Hardhat flatten task by addressing cyclic dependency issues. Introduced a 3-color iterative depth-first search algorithm in TypeScript to detect cycles explicitly, replacing the previous silent failure mode. Implemented detailed error handling with the FLATTEN_CYCLIC_DEPENDENCY (HHE602) descriptor, which reports all files involved in a cycle, improving transparency for developers. Added fixture projects and comprehensive tests to ensure robust coverage of cyclic dependency scenarios. This work focused on error handling, Solidity integration, and testing, ultimately reducing debugging time and preventing incorrect build outputs for projects using the flatten feature.