Whole-set density pass (owner doctrine: each axis gets its own pass). Fresh single-navigation iframe per template at 1280px (compact's home context — it is pointer-fine-gated), data-cs-density="compact" forced on the document element, settle, then fail on any document-level horizontal overflow. Compact only tightens control metrics, so overflow indicates a control that leaks its box when shrunk. window.__density.pass must be true.