The three mixing matrices of the Standard Model — CKM (quarks), PMNS (neutrinos), and the trivial identity matrix (charged leptons) — are shown to be three manifestations of a single exponential decoherence process in generation space. The base decoherence rate gamma = N_c x T_F = 3/2 approximately reproduces the Cabibbo angle from the color gauge group (0.6%, 3.5 sigma). Four empirical constraint equations relate the full CKM matrix to quark masses with no free parameters. The framework also predicts two PMNS mixing angles from quark masses: sin(theta_12)^PMNS = sqrt(m_c/m_b) = 0.551 (measured 0.550, 0.14%) and sin(theta_13)^PMNS = sqrt(m_s/m_b) = 0.149 (measured 0.148, 0.71%). All predictions are falsifiable by next-generation lattice QCD and neutrino oscillation experiments. ---Boundary Wave Framework Series (all submitted to Physical Review D):1. One formula for all fermion masses — https://zenodo.org/records/195787572. Decoherence spectrum of the Standard Model — https://zenodo.org/records/195787963. Fermion generations as standing wave nodes — https://zenodo.org/records/195788674. Electroweak masses and CP violation — https://zenodo.org/records/195789295. Strong sector, confinement, and hadron masses — https://zenodo.org/records/19579136