Worked on the google/mozc repository to deliver a backward compatibility fix for candidate window display in mozc.el, ensuring stable functionality across different mozc_emacs_helper versions. Addressed a bug by supporting both legacy and current field names, prioritizing candidate-window when available, and simplifying candidate field handling using Emacs Lisp. Enhanced code readability and maintainability by replacing complex bindings with let expressions and or-logic for field resolution. Incorporated targeted debug logging and inline documentation to clarify backward compatibility decisions. Responded to reviewer feedback to minimize regressions, ultimately reducing maintenance overhead and supporting consistent candidate display for Emacs users across multiple versions.