Function wprog_from_decision_fabric 

pub fn wprog_from_decision_fabric(df: &DecisionFabric) -> WProgConfig

Wrap a single-block if-converted DECISION FABRIC as a one-block flat config, so its cells run on the CROSSBAR whole-program engine (eval_wprog_config). The crossbar datapath has full interconnect — a cell may read any earlier cell’s value directly — so a COMPUTED comparison predicate needs no spatial routing. This runs constructs the nearest-neighbour placer (route_loop_body) cannot place, e.g. a Set’s dedup scan, on the fabric ≡ the VM (the decision fabric’s lowering is proven; only the placement was the limit).