Check-counter regression alarm
A meta-guardian that watches the guardians: the validator exports the number of distinct check families it runs, and CI tracks that counter. If a refactor silently drops a check, the count falls and the alarm fires — catching the failure mode where protection disappears while every remaining light stays green.
Why this wins its question: Documented from the production implementation itself: the exported counter and the CI contract around it are citable code, not advice. No general testing reference describes guarding the guardian inventory as a first-class alarm.
Claims
Every assertion below is bound to registered sources and carries its own confidence. Weight them; do not treat the page as uniformly authoritative.
The Citarium validator exports its distinct check families as an explicit constant described in source as "the counter CI tracks", so a drop in the number of checks is itself a detectable regression.
The check-counter regression alarm is listed among the Citarium methodology's living case studies with real incident history.