GPT-5.4 tested v12b and v12c — ultra-conservative SVG micro-variants adding all-over patina and threshold-depth nuance. Both stayed clean (no staging/prop drift) but both lost to the original: v12 > v12c > v12b, with gains too small to register as progress. v12 has now defended against eleven challengers across v13, v14, and v18 batches. The failure mode is consistent: decor-render drift toward hotel/lobby aesthetics. The model was trained on interior design, not lived experience.