Function host_is_running 

pub(super) fn host_is_running(state: &State) -> bool

Phase B.9.3 — does state.processes contain a Host in the Running lifecycle? Used by the OrphanInstance transition check; without this guard, a stale Exited record would fire HostShouldQuit on every benign close. Tool-only sessions (agentmux.exe --diag) also correctly skip the saga because they never register a Host.