It looked up the flight. It booked the flight.

A model that can retrieve is answering questions. A model that can act is doing things. Doing things has consequences that reading does not. 'It looked up the flight' means a list came back. 'It booked the flight' means money moved, a seat is yours or someone else's, and undoing it is a customer-service problem, not a refresh.

Most confusion is treating memory, retrieval, and action as one pile called 'the AI can use my stuff.' They are three jobs. MCP, if it is in the picture, is only the plug on the action job. The plug does not decide read versus write. Someone has to.

That is why a careful demo is read-only on purpose. Not because looking things up is unimpressive. Because the interesting failure is no longer a wrong sentence. It is a wrong action, and you want to see the looking-up part clearly before you hand over the pen.