CDN-253: The Universality Test — Five-Survey Validation of the Locked GCFT κ-Proxy Across 10,793 Galaxy Clusters

CDN-253 completes the survey-validation phase of the GCFT dark-sector cluster programme. The locked CDN-242 κ-proxy is tested on Planck PSZ2, adding a fifth independent survey to previous validations from lensing, SZ, and X-ray selected cluster catalogs. The combined sample spans 10,793 galaxy clusters across five surveys and redshifts from z = 0.01 to z = 1.91. Results show consistent proxy performance across all major public cluster catalogs, no evidence for redshift evolution in the mass–κ relationship, and a clearly identified domain boundary near M200 ≈ 1 × 10^14 M☉. The study characterizes the proxy's universality, establishes its practical validity range, and concludes the large-scale survey validation phase of the GCFT cluster arc while outlining remaining theory-debt and group-scale reformulation tasks.