Worked on strengthening transaction validation within the ethereum-optimism/optimism codebase, focusing on backend and blockchain development using Go. Addressed a validation flaw by implementing a targeted guard in the batch validation pipeline, specifically preventing SetCode transactions from being embedded before the Isthmus. This change reduced the risk of invalid states and improved the correctness of transaction processing. The solution involved a precise, maintainable update with a small surface area, enabling safer upgrades and minimizing risk for downstream validators. The work demonstrated a methodical approach to improving reliability and security in end-to-end transaction validation without introducing unnecessary complexity.