Function check_structured_dag 

pub fn check_structured_dag(nodes: &[SNode]) -> bool

The checker: ⊥ leaves carry the empty clause; structured leaves re-fire their specialist (the dispatcher’s route re-checks internally — an idempotent re-verification); internal nodes’ children are exactly their recomputed Shannon cofactors. The internal skeleton is fully zero-trust; the structured leaves are dispatcher-certified (extracting each route’s own witness for end-to-end zero trust is the next hardening).