Worked on the elastic/package-spec repository to deliver support for the 'lookup' index mode in Elasticsearch transforms, enabling the creation of lookup indices for ES|QL JOIN operations. This feature expanded data integration capabilities by updating schema definitions and compliance tests to accommodate the new mode. The implementation included a dedicated test package to ensure robust validation of the lookup index functionality, with all changes clearly traceable through the associated commit. The work demonstrated proficiency in Go and YAML, as well as skills in data modeling, ESQL, and testing, focusing on maintainability and comprehensive test coverage within the codebase.