Function recognize_gated_delta 

pub fn recognize_gated_delta(stmts: &[Stmt<'_>]) -> Option<GatedDeltaSpec>

Recognize Let O be gated delta of Q over K and V with gate Z beta B decay A state S norm GN with HV heads HK groups — the head loop opened by the (head−1) mod HK key-head binding, the in-place S update, and the gated norm that writes the head.