Exact rank 9 established by Magma 2-descent. Independence also checked using a 10x10 mod-3 reduction matrix including the rational 3-torsion point, with determinant 2 mod 3. Found by a precomputed Mestre–Nagao sieve of the rank-5 C3 K3 deformation, specializing w=7/4, t=81/64.
jesper-petersen ·