Run the gateway daemon: rename the process, detach from the controlling
terminal, and serve until ShutdownGateway. selfcheck_marker is a
test-only path written with the platform’s detachment proof once bound.
Rename the running process so process managers can distinguish the gateway
daemon from interactive term-session clients. Best-effort and cosmetic:
a failure is ignored and never affects functionality.
Connect to the gateway daemon and run op with a live client. The tokio
runtime that hosts the muxio connection is kept alive for the whole op,
so RPCs complete (dropping it early would tear down the connection and
hang the call). op receives an owned Arc and runs on that runtime.