Galactic Sector Completion: No-Go Theorems and Kinetic Screening

We prove three no-go theorems establishing that the minimal RCD action and its two simplest extensions cannot produce O(a_0) galactic effects. We then construct Completion B', the minimal kinetic extension K(X) = X + X^2/X_* with conformal matter coupling A(C) = 1 + beta*f(C), that restores galactic phenomenology through k-mouflage screening. The theory is ghost-free, gradient-stable, and subluminal. The screening mechanism produces a universal transition acceleration a_trans independent of system mass. The viability window for X_* spans ~15 orders of magnitude. Five independent observational kill switches are identified.