Concept
A machine front door names a reachable human
The /.well-known/agent document must declare who is accountable — an org id and a named, reachable human — because a door with no one behind it is not a door.
Pinned to
agent/1 — the discovery documentThe canonical source this concept is taught from. If it moves, the lesson is regenerated — teaching is pinned to code, not retyped.
On the frontier
No course teaches this concept yet — it is a named gap on the content graph, not a hole nobody sees. A gap is the roadmap, not an embarrassment: the count only falls by teaching.