Beto Trevisan enhanced user experience and error handling across the livebook-dev/livebook and gleam-lang/gleam repositories during December 2024. He refined the session closure UI in Livebook so that danger hints now display only when a session lacks an associated file, reducing unnecessary warnings and clarifying user guidance. In Gleam, he improved error messages for variant-custom types, providing developers with actionable feedback when fields are inconsistently defined. His work demonstrated proficiency in Elixir, Rust, and compiler development, with a focus on user-centric design and robust error handling. The changes were well-tested and documented, reflecting thoughtful, targeted engineering contributions.