CDN-251: The Cross-Survey Test — Locked κ-Proxy on 516 SPT-SZ Clusters

First execution of the CDN-242 κ-proxy on a completely independent survey. The seven-term logistic proxy, trained on 25 CLASH lensing clusters and locked since CDN-243, is applied to 516 confirmed SPT-SZ 2500d clusters (Bocquet et al. 2019) with no overlap in selection function, mass calibration, or observing strategy. 337/516 are cross-matched with eROSITA DR1 for real X-ray morphology. Result: PASS — 510/516 (98.8%) in-band by CDN-249 empirical bands, 0 cap violations, 99.13% mean closure. The CDN-242 population bound (≤0.29% non-GCFT dark matter) holds at scale. Includes execution script, full per-cluster results JSON, and Art Edition.