Foundation I: The Metric Universe - Extended Version

We investigate a minimal cosmological extension of General Relativitybased on the Einstein-Cartan-Kibble-Sciama (ECKS) framework. A primordialspin component — with stiff equation of state w=1, geometrically distinctfrom scalar kination — induces a transient phase reducing the comovingsound horizon to rₛ = 135. 8 Mpc, enabling H₀ = 73. 0 km/s/Mpc consistentwith local measurements. The same stiffness parameter Fᵢon = 1. 2765governs both sound-horizon reduction and scale-dependent suppression ofstructure growth (S₈ = 0. 766), unifying H₀ and S₈ under a single degreeof freedom. A global MCMC fit yields Δχ² = −39. 5 vs ΛCDM (AIC = −31. 5, BIC = −8. 2). Resolving H₀ natively exposes an irreducible H₀–Age–BAOtrilemma, predicting t₀ = 12. 74 Gyr — now corroborated by H0DN 2026 (H₀ = 73. 50 ± 0. 81 km/s/Mpc, >6σ tension). Additional falsifiablesignatures: cosmic birefringence βECF ≈ 0. 35° (LiteBIRD), JWSThigh-redshift seeds, and a blue-tilted primordial GW background. ── Version notes (v2) ───────────────────────────────────• Sec. 2: ECKS algebraic torsion identified as low-energy limit (mT≫H) of the extended Poincaré Gauge Theory (PGT) framework of Foundation II — eliminates F1/F2 theoretical inconsistency. • Sec. 1: H0DN 2026 result (H₀=73. 50±0. 81, >6σ) and Kouniatalis falsification table overflow fixed.