Expansion-Shadow Gravity with Spin

Minimal flat-background gravity theory with two mediators (massless spin-2 + trace-coupled scalar) that matches classic GR tests locally. A brief pre-recombination energy pulse reduces the sound horizon by ≈9%, mapping transparently to H₀ ≈ 74 km s⁻¹ Mpc⁻¹; the claim is falsifiable by CMB/BAO fits. Preprint (v1), not peer-reviewed.