saveHeartbeat

Persist the engine-observed last-heartbeat timestamp for nodeId.

The engine updates this on every frame it observes from a node (periodic heartbeats, telemetry, forwarded packets, ...). Persistence is what keeps presence state alive across process death: on the next RadioClient.connect the engine calls loadHeartbeats and rehydrates its in-memory map so subscribers don't see every previously-known node as "silent since boot".

Implementations should upsert the row for nodeId without touching any other columns on the node (in particular, not resetting NodeInfo fields).

Parameters