Developed a PRINT_APP host-to-guest messaging feature for the streamlit/streamlit repository, enabling embedding hosts to programmatically trigger the browser print dialog within embedded Streamlit apps. This work involved end-to-end updates across the messaging protocol, TypeScript typing, and React-based UI wiring, with a focus on improving dashboard and report print workflows. The implementation included architectural changes to the HostCommunicationManager and App.tsx, as well as comprehensive unit and integration tests using JavaScript and TypeScript. Enhanced cross-frame printing user experience was achieved through iframe compatibility and a polling-based readiness check, reflecting a thorough approach to front end development and testing.