Worked on the nextcloud/mail repository to deliver a drag-and-drop enhancement focused on supporting multiple independent DroppableMailbox instances within complex mail user interfaces. The solution involved refactoring instance management by replacing array-based storage with a WeakMap, enabling O(1) lookups and improving performance in large-scale UIs. Leveraging JavaScript and Vue.js, the developer enhanced event handling and instance tracking to ensure reliable and scalable drag-and-drop functionality. Copilot-driven suggestions and targeted refactors were incorporated to improve code quality and maintainability. The work emphasized front end development best practices and included unit testing to ensure robust, maintainable, and efficient feature delivery.