IV.P197 — eta_bar from CP Phase Structure: Best tau-Candidate sqrt(5)/(2*pi)

Conjectural: eta_bar from systematic tau-scan. Best close candidate: sqrt(5)/(2*pi) = rho_bar*sqrt(5) = 0.35588 at +22647 ppm from PDG 0.348. Also: kappa_D - iota_tau = 0.31739 at -87955 ppm; kappa_omega*(1+kappa_omega) = 0.31921 at -82743 ppm. None achieve tau-effective precision. The ratio eta_bar/rho_bar = 2.189 approx sqrt(5) = 2.236 at +2.1%. Structural interpretation: eta_bar = sqrt(5)/(2*pi) would connect the CP phase to the golden ratio phi = (1+sqrt(5))/2 via eta_bar = (sqrt(5)-1)/(2*pi) + rho_bar. Open question (OQ-CKM1).