The Rejection Register

Twenty-two named ways the model says no, and a property asserting that every one of them is produced by a live vector.

Why the register is the useful artefact

Two implementations agree about success trivially and disagree about failure constantly. "It rejected the request" is not interoperability. "It rejected the request with meet-not-colocated" is.

This is the piece of the DTG conformance work that turned out to be worth the most, and nobody expected it to be.

The discipline

A register entry nobody can produce is a documentation claim, and documentation claims are what this whole way of working exists to replace. So the coverage property is not optional decoration — it is the thing that keeps the register from rotting into prose.

A second property asserts the reverse: no vector may produce a code that is not in the register. The vocabulary is closed in both directions.

Absence has reasons too

The overlay query can be asked to explain itself, returning every pin that could have appeared and did not, each with a named reason: out of radius, no trust edge, below the freshness horizon, capped private by its owner, ranked out beyond the cap.

A desk demo with an empty overlay should be able to say why in one call, instead of by bisecting the query. See Erosion Is A Rate Not A Cliff for the horizon and Audience Is Granted Not Computed for the cap.