v = V·S/(Km+S) at S = Km ⇒ v = V/2 (half-saturation anchor)

Sympy-exact witness of the K_m = S = half-V_max defining identity. Setup: v(S) = V·S/(K_m + S). Substituting S = K_m gives v = V·K_m/(2 K_m) = V/2 exactly (sympy simplify → V/2). Oracle pins: v_at_S_equals_Km = 'V/2',…