CDN-293: The Sputter Map

CDN-293 converts the CDN-292 rheology wall into a test-class map for the GCFT dynamic Xi channel. The note defines the drive number D_Xi = |v_r|/v_star, the coherence window W_R, the sputter index S_Xi = 1 - W_R, and the dynamic-test eligibility Q_Xi = P_r W_R. It classifies solar-system flybys and disk vertical crossings as low-drive dynamic tests, stellar streams and local-group infall as wall tracers, high-velocity stars and cluster mergers as freeze-out checks, static rotation curves as Channel-A anchors, and relativistic ejecta as out of scope for this nonrelativistic dynamic-channel map.