Emergent Cosmological Constant from Self-Organized Quantum Vacuum Boundary Conditions

his paper presents an emergent formulation of the cosmological constant ($\Lambda$) derived from macroscopic quantum vacuum boundary conditions at the Hubble horizon. Regulated by a critical acceleration threshold $a_0 \approx 1.2 \times 10^{-10}\text{ m/s}^2$, the model yields an exact vacuum energy density $\rho_{\text{vac}} = 3a_0 H_0 / (8\pi G c) \approx 5.3 \times 10^{-27}\text{ kg/m}^3$, perfectly matching Planck observational data without fine-tuning. Includes a 5-test quantitative numerical validation suite and full code reproducibility.