Worked on enhancing the UnionJoin functionality in the zipline-ai/chronon repository, focusing on improving reliability and consistency in data processing workflows. Developed a feature that preserves left passthrough columns in join outputs and introduced configurable naming conventions for output columns, allowing users to choose between long-name and short-name formats. Unified the behavior of fast-path and regular joins to minimize regressions and ensure deterministic outputs, which simplifies downstream analytics. Expanded unit testing to cover both naming schemas and group-by derivations, using Scala and Spark to implement and validate these changes. The work emphasized maintainability and clarity in join operations.