A 20-year-old graph theory conjecture has fallen. Claude Opus 5 proved that Conjecture A.312 (2006 thesis, Sec. A.5.8), which claimed a*D ≤ 2n−4 for all connected graphs, fails at the simplest possible counterexample: K2 itself (a*D = 2, bound claims 0). The verifier returned 239 checks run, 239 passed, 0 failed.