Worked on enhancing Vue custom elements within the vuejs/core repository, focusing on improving their reliability and interoperability in complex front end scenarios. Addressed challenges related to shadow DOM parent resolution for slotted content and refined attribute and property handling for asynchronous components. Leveraged Vue.js and TypeScript to implement these changes, ensuring that custom elements behave predictably across shadow DOM boundaries. Added comprehensive tests to validate the new behaviors and prevent regressions, contributing to a more robust and maintainable codebase. The work resulted in improved component composition and reduced runtime edge-case errors for developers integrating Vue custom elements in diverse projects.