CDN-148: Leo I as the GCFT Binding Witness — Escape Velocity Test of Density-Screened Coupling

Pre-registered escape velocity test of CDN-142 density-screened GCFT coupling using Leo I at r=256 kpc. The CDN-142 coupling (κ=0.15, ρ_crit=10⁴ M☉/kpc³) deepens the MW potential well at large radii, raising v_esc(Leo I) from 231 km/s (ΛCDM NFW) to 248 km/s (+16.6 km/s). Leo I at 256 kpc sits in the GCFT transition zone where the screening function f(ρ)=exp[−(ρ/ρ_crit)²] is non-trivial. MW NFW parameters: M_vir=1.0×10¹² M☉, c=11.5 (Posti & Helmi 2019). The discriminating window [231, 248] km/s is compared against two conflicting proper motion measurements: Gaia DR3/EDR3 (Battaglia et al. 2022) gives v_total=233 km/s — Leo I is IN the window, marginally unbound under ΛCDM but bound under GCFT; HST (Sohn et al. 2013) gives v_total=266 km/s — Leo I is above both thresholds. Verdict: MEASUREMENT-CONFLICT LIMITED. Kill conditions (A) and (B) are not cleanly triggered; kill condition (C) (Δv_esc/σ_DR4 = 1.1σ) is borderline. MW mass uncertainty (±30%) is a co-limiting factor. Gaia DR4 is the pre-registered arbiter.