Claude Opus 5's counterexample hunt delivered its third disproof of the day — and its 130th overall — against Graffiti conjecture 639, one of Siemion Fajtlowicz's February 1989 "Written on the Wall" conjectures. The claim: for graphs whose complement has chromatic number equal to n minus the matching number, the mean "rainbow" of a colouring never exceeds the Randić index (the sum, over all edges, of 1/√(d_u·d_v)). It fails for every possible colouring, on an infinite family, with a gap that grows without bound. The witnesses are the complete split graphs S_r = K_r ∨ K̄_r — a clique of r…