Vacuum Metastability, Cosmological Tensions, and Gravitational Wave Signatures of the Bio-Cubic Universe MCMC v3 Consolidated Results — 9 Parameters — 1,280,000 Samples

We present consolidated results from the third MCMC run (v3) of the Bio-Cubic cosmological model, a framework derived from Loop Quantum Gravity (LQG) in which spacetime at the Planck scale is organized as a nested cubic lattice. The model introduces a running effective gravitational constant G_eff(z) modulated by inter-level phase decoherence, which simultaneously addresses the S8 tension, the H0 tension, and provides a natural mechanism for vacuum metastability through the Coleman-De Luccia bounce action augmented by quantum decoherence. The MCMC v3 run employs 9 free parameters, 128 walkers, 10,000 production steps (burnin = 800), and 1,280,000 total samples on a 4-core laptop (Ploumagoar, Brittany, seed = 137). Key results: the spectral index n = 2.035 +/- 0.48 is confirmed for the sixth time independently, robustly placing the Bio-Cubic model in the Z2 universality class. The decoherence parameter beta = 0.089 +/- 0.039 is detected at more than 2 sigma from zero. The single ratio g/lambda = 1.93 simultaneously controls three independent cosmic observables — the S8 tension, the H0 tension, and the vacuum lifetime — constituting what we call THE TRIPTYQUE. The Bayesian evidence ln(B12) = +13.03 is decisive on the Jeffreys scale, stronger than the Paper IV result (+9.80) despite three additional parameters, demonstrating that the Occam penalty is overcome by improved data fit. The vacuum is confirmed stable with beta_crit = 0.600 (margin 13.6 sigma) and log10(tau_vide) = 176 years. The gravitational wave signature Omega_GW ~ 5.9 x 10⁻¹² at f ~ 0.01 Hz lies below the LISA Pathfinder upper limit and within the detection horizon of the LISA mission (2034-2037).