The hard part of LLM apps, made visible.

An MCP shopping app where three actors share one state: the user editing a cart, the view rendering it, and the model reasoning about it. Touch any one and the other two stay in sync — in both directions. Most demos claim this. This one lets you watch it happen.

This is also a real MCP endpoint. Point an MCP client (ChatGPT, Claude) at POST /mcp to open the same store inside a conversation.