Geometric Origin of Macroscopic Gravitational Normalization at Radiative Boundaries

Dark energy, the vacuum discrepancy, and the Hubble tension are usually treated as separate problems. This essay argues that they arise from a single dimensional error: modeling cosmic expansion as a bulk 3D fluid rather than a boundary-normalized 2D constraint. Imposing thermodynamic equilibrium strictly at a radiative decoupling surface yields a mass-independent geometric invariant, pi^3/15 ≈ 2.0671. Projecting this boundary limit to the cosmic horizon gives the empirical dark-energy fraction, Omega_Lambda = pi^3/45 ≈ 0.689, without free parameters. Spatial flatness fixes the complementary matter fraction, Omega_m ≈ 0.311. The same partition sets the onset of acceleration at z_acc ≈ 0.642, naturally relaxes early dark matter requirements, and places the H0 tension in an effective topological framework. Gravity is therefore treated not only as a local metric field, but as a macroscopic constraint fixed at radiative boundaries.