Package runneractivity carries only current-connection activity between the
proxy and daemon. It is not audit storage; reconnect invalidates all markers.
Record coalesces live activity. Caller serializes writes; no durable replay
path calls it. Offline admission (nil epoch) cannot produce an activity signal.
Read observes a whole replacement without deleting it: deleting after a read
could erase a newer concurrent writer. The daemon deduplicates ID in memory.