D5: the copied witness on a parameter commutator

The result is observation-qualified. For example, $f=0$ makes the pairing vanish and removes this detection argument. We do not assert obstruction for every frozen observation, every mass, or every conceivable correction class. For the detecting fixed data, however, the exclusion applies to every member of the class, not merely to one candidate.

The witness is a classical test of the correction interface. It is not a binary quantum anomaly.