Concept
A gateway that did not forward must not return 200
The one thing a gateway must never do is fabricate a receipt: if it did not actually reach the origin, it cannot report success.
Pinned to
bastion — the commercial gatewayThe 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.