Andrej Rakic refactored the MockCCIPRouter in the smartcontractkit/ccip and smartcontractkit/chainlink-evm repositories to support EVMExtraArgsV2, expanding the CCIP protocol’s execution parameters while maintaining backward compatibility with V1. He updated internal logic to handle both argument versions, ensuring robust handling of new and legacy data. Andrej implemented comprehensive unit and integration tests in JavaScript and Solidity to validate correct behavior and error handling for both V1 and V2 inputs. His work focused on smart contract development and testing, reducing integration risk for downstream applications and improving the developer experience through enhanced protocol flexibility and reliability.