V.D293 — Defect Fraction Function

Defect fraction f_def(z) = S_def(z)/(S_def(z)+S_ref(z)). At z→∞: f_def→1 (defect-dominated). At z=0: f_def→ι_τ³≈0.040 (refinement-dominated). Controls effective equation of state via w(z) = −1 + (2/3)·f_def/(1−f_def).