Shared state every search/get/call tool method needs. Clone
because rmcp constructs one instance per session (see
http::server::start_http_server’s service factory) — every field is
either cheap to clone (String, Config) or already Arc-wrapped.
Runs server over the stdio transport until the client disconnects —
the Terminal Client / Harness Server “stdio” mode’s connection point
(Story R5 wires this into main.rs’s subcommand dispatch).