Function genus2_jacobian_order 

pub fn genus2_jacobian_order(sextic: &[BigInt], p: &BigInt) -> i128

#Jac(C)(𝔽_p) for the genus-2 curve C: y² = f(x) (deg f = 6, monic), from its L-polynomial via the point counts over 𝔽_p and 𝔽_{p²}. For a split Jacobian Jac(C) ~ E₁ × E₂ this equals #E₁·#E₂ (Tate: isogenous abelian varieties over 𝔽_p share their order) — the exact point-count validation of a gluing.