A mini app is appropriate when chat buttons are insufficient: catalogues, calendars, long forms, maps, and tables work better in a web interface inside the messenger. I build that UI against shared server logic.
Scope includes responsive UI, launch-signature verification, sessions, APIs, returning results to chat, and Telegram/VK/MAX specifics. Acceptance checks trusted identity server-side, safe repeated saves, preservation of input through network errors, and agreed screen sizes. A full offline mobile app is a separate product, while a simple form rarely needs a mini app.
