BCT Letter 21: The Muon and Tau Masses from BCT C4v One-Loop Geometry — Koide Angle Correction

We derive the muon and tau masses from BCT C4v one-loop geometry via a Koide angle correction δθ_K = ε2/(16π). The results m_μ = 105.658 MeV and m_τ = 1776.84 MeV agree to sub-0.02% (Predictions #94 and #95), bringing the BCT programme to 95 sub-1% predictions. All three charged lepton masses are now derived from a single geometric input.