Concept
Same-domain, with no suffix guessing
Redirects are followed only within the same domain over https, host-or-subdomain — there is no Public Suffix List in the checker, so it refuses to guess rather than read two publishers as one.
Pinned to
agent-dns/1 — the discovery naming layerThe 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.