The presenter view said "1 phone connected". The phone was in a pocket, screen off, and the presenter had already pressed Disconnect. Nothing changed.

That bug, and the Durable Objects behaviour behind it, is a good way into the live room in Kadal Deck, which we launched this week. A talk is one MDX file, and every published deck gets a room: the audience scans a QR code, with no app and no login, and their phones follow the slides, answer polls and quizzes, ask and upvote questions, and react. The presenter's phone can be the remote. It runs on Cloudflare Workers, with one Durable Object per room.

This post is about how we built that room, what we traded away, and what broke.

Why not just link to a polling app?

Most interactive talks use two products: the slides, and a separate audience tool.…