UI Composition with Application Frontend Service

Why shared UI code is hard, and what Application Frontend changes about it. The piece first lays out the three usual answers and what each costs — copying files at development time and repatching every consumer, publishing an npm package and rebuilding every consumer, or hosting the code separately and paying for it in CORS and session handling, or in an extra network hop through a server-side proxy. It then shows a fourth that only this service can do: runtime server-side composition without the hop, configured through routes in the consuming application's xs-app.json, across three cases — a reusable application embedded in a consumer, and two further composition shapes. Read alongside the generator, which scaffolds the mta.yaml, xs-app.json and zipper configuration this model needs.