Two tasks: (1) the cost_graph(Vec<PrimitiveBuilder>) -> Composite builder in
aura-composites + the GEOMETRY_WIDTH re-export from aura-std + two unit tests
pinning the exposed input-role set and the 3-field output; (2) the aura-cli
stage1_r_graph rewire onto cost_graph, deleting MAX_RUN_COST_NODES and
COST_SUM_PORTS. Runtime port names .leak()'d (the risk_executor precedent).
Behaviour-preserving: the cycle-3 net_expectancy_r goldens are the regression net.
refs #148
Brummel
550d5ce947