Cassio worked on the Shopify/ruby-lsp-rails repository, focusing on improving the robustness of the Ruby LSP hover feature and enhancing database indexing. Addressing a bug where index columns were inconsistently handled as Arrays or Strings, Cassio refactored the hover functionality to process both types correctly, resolving errors and improving developer experience. He introduced a new unique index on the users table to strengthen data integrity and updated related tests to ensure accurate coverage of the new behavior. Utilizing Ruby, Ruby on Rails, and test-driven development practices, Cassio’s work contributed to more reliable code and reduced regression risk in the project.