A Grommer-type Hankel tower for the Riemann Hypothesis: a certified rank, a Davenport–Heilbronn test, and the detection range of off-line zeros

Numerical study of a known equivalent form of the Riemann Hypothesis (Grommer-type Hankel positivity for Y(w)=ξ(1/2+√w) at w=9/4). No proof of RH and no new criterion is claimed. Contributions: independent recomputation of a certified rank-16 pivot; a Davenport–Heilbronn test (positive up to rank 73, first negative pivot at rank 74); detection range of injected off-line zeros compared with Li's criterion; Padé localisation of off-line zeros; quantification of the Gamma–prime compensation; a list of refuted proof strategies. Includes Python/mpmath code and raw outputs. Prepared with the assistance of an AI system (Claude, Anthropic).