world-presence
The push half of world embodiment. world-look answers "who is here?"
when the agent thinks to ask; this fires when the answer changes, so
the agent can notice someone arriving without being prompted.
What it reports
Transitions, not state. A level-reporting sensor on a 30-second schedule would emit "Bruce is still standing there" a hundred times an hour, and every emission costs a full agent turn. So it stays quiet while nothing changes, and speaks when someone crosses the proximity boundary in either direction.
But it carries state in the payload. A bare "Bruce arrived" would
force a world-look before the agent could say anything useful — a
wasted iteration on every wake. The event ships the current positions,
distances and ground with it, so the first iteration can already act.
Current presence at any other moment is not this sensor's job: the
system prompt's Embodiment block carries who is in the world, and
world-look answers on demand.
Hysteresis
enter_m (12 m) is closer than exit_m (20 m) on purpose. With one
threshold, someone standing near the boundary flaps arrive/leave on
every tick and buries the agent in turns. Crossing in costs 12 m;
crossing back out costs 20 m.
Cold start
The first run after launch records who is nearby and emits nothing. Someone already standing next to you when the process starts is not news — that is the Embodiment block's job — and firing on it would make every restart look like an arrival.
Quiet when the world is down
If the world server is unreachable the sensor reports nothing rather than erroring each cycle. A world that is not running is the normal case for a chat-only session.