MCP (Model Context Protocol) is how an AI host like Claude Code talks to your tools. A server you build is a thin governed gateway: Claude never touches the database — it calls your tools, which run your validated Core services. The payoff in this lab is the through-line from C4: the same IReadingProgressService you wrote on Day 1 becomes reachable a third way — first as an HTTP endpoint (C4), then as an in-process agent tool (C6), and now as an MCP tool any host can call (C8). One service, three surfaces.
