A.21:1 - Problem frame

A gate combines results defined elsewhere. A.20 may report an internal constraint; A.10 or B.3 may support an evidence or assurance check; E.18 may establish a structural crossing; a regulatory or safety pattern may define another criterion. A.21 does not redefine those truths. It records how one applicable profile maps their results to one bounded decision.

The gate is optional. A guard, dashboard, readiness label, plan item, path boundary, or publication form does not create a gate decision by resemblance.