The U-Cell Model Prediction w=−1 Exactly: A Sharp Falsifiable Test Against DESI DR1 Baryon Acoustic Oscillations

The U-Cell Model (UCM) predicts w=−1 exactly for all redshifts, because the Hubble constant H(z) cancels identically in the void–halo balance that determines Omega_Lambda,0 = 0.6834. We test this prediction against all 13 DESI DR1 baryon acoustic oscillation measurements and find chi²/dof = 1.54, marginally better than Planck ΛCDM (Δchi² = −0.42). DESI BAO alone gives w = −0.99 ± 0.14, fully consistent with UCM. A sound-horizon-independent ratio test D_M/D_H confirms the result. The model makes a sharp prediction: Euclid DR1 (October 2026) will find w = −1 to sub-percent precision, or falsify the mechanism.