Function ping 

pub fn ping(pc_id: &str) -> String

agents.<pc_id>.ping — v0.38 / #133 request/reply for the active “ping” round-trip. The agent answers with a fresh Heartbeat on demand instead of the backend waiting up to ~30 s for the next periodic heartbeat tick to land. Distinct subject from heartbeat.<pc_id> so the periodic publisher is unaffected and old agents that don’t subscribe simply time the request out.