Structure sanity card v4.5. Adds the prototype symmetry check: when a prototype is declared, detected sweep symmetry is compared against the prototype's space group; the tight-child/loose-parent signature is surfaced as a coherent subgroup distortion with an estimated amplitude, instead of being buried in a FRAGILE note that framed the tight result as noise. Calibrated on the subgroup-distortion ladder (rms reads 0.50x true amplitude, 0.04-0.4 A window) and re-run on the 105-case corruption battery with zero errors and no verdict regressions.