This repository contains Version 2 of Coherence Gravity: A Cubic Vacuum Field Theory with Thermodynamic Relaxation. Coherence Gravity (CG) proposes that gravitational phenomena arise from the elastic and thermodynamic response of a cubic-rigid vacuum medium rather than from non-baryonic Dark Matter particles. The theory is formulated as a covariant, ghost-free scalar-tensor field theory with a cubic kinetic term X∣X∣X \sqrt{|X|}X∣X∣ and a finite entropy-dependent relaxation time τ(S)\tau(S)τ(S). Version 2 includes: Full covariant Lagrangian and field equation derivation Stability analysis (hyperbolicity, absence of Ostrogradsky ghosts, subluminal propagation) High-Mach cluster dynamics (Bullet Cluster, Abell 520) with entropy-gated vacuum decoupling Solar System and binary pulsar consistency checks Gravitational wave propagation constraints (∣cT/c−1∣<10−15|c_T/c - 1| < 10^{-15}∣cT/c−1∣<10−15) Linear perturbation analysis and effective gravitational coupling Geff(z)G_{\mathrm{eff}}(z)Geff(z) Explicit falsifiability criteria and parameter-minimal structure The framework produces quantitative, testable predictions across galactic, cluster, and cosmological scales, including: Flat galaxy rotation curves without particle Dark Matter ~10% forward lensing asymmetry in high-Mach mergers Mach-number scaling of vacuum decoupling Late-time enhancement of structure growth fσ8(z)f\sigma_8(z)fσ8(z) Cosmic age prediction (~14.5 Gyr under fiducial parameters) The theory is parameter-minimal: once α0\alpha_0α0 is fixed by galactic rotation curves and standard cosmological parameters (Ωm,H0\Omega_m, H_0Ωm,H0) are measured, the expansion history follows from a cubic Friedmann equation. Crucially, CG is falsifiable. It would be ruled out by: Significant deviation in multimessenger constraints on gravitational wave speed Absence of predicted lensing skew in high-Mach cluster mergers BAO-derived H(z)H(z)H(z) evolution incompatible with the cubic expansion law This version consolidates the theoretical foundations and organizes observational discriminators into a structured experimental roadmap.