Split-prime supercongruence at the mixed CM point (1/6, 1/3; 1)

For the mixed CM point (a, b, c) = (1/6, 1/3, 1), define A_n^mix := 108^n [z^n] ₂F₁(1/6, 1/3; 1; z)^3. For every split prime p ≥ 7, p ≡ 1 mod 3, and every m ≥ 1, A_{mp}^mix ≡ A_m^mix (mod p^4). The exponent 4 exceeds the generic weight-3 Hodge-gap prediction of 3; the extra factor of p is a CM enhancement attached to j = 0. The matching unconditional inert-prime obstruction (p ≡ 2 mod 3) is also established. The proof uses the modular realization on Γ_0(3) with parameter t = u/(1+27u)^2, a Lagra