bind_loopback() refuses to bind anything that doesn't resolve to a
loopback address -- unit tested directly (non-loopback IP, unparseable
host, and a real 127.0.0.1:0 bind). serve() runs a hyper HTTP/1 accept
loop in front of rmcp's StreamableHttpService (a bare tower_service, not
an axum app); every request needs `Authorization: Bearer <token>`
(constant-time compared via mcp::token::verify) before it ever reaches
the MCP service -- an unauthenticated request never reaches rmcp at all.
iamdoubz
9eed88e5bd