“Even if this were an accurate characterization of the Government’s position, the argument belies our precedents. In determining whether the discretionary-function exception applies, we ask whether the challenged conduct is ‘susceptible to policy analysis,’ not whether it was in fact subjected to that analysis by the decisionmaker,” Judge Bobby Ed Shepherd wrote on behalf the Eighth Circuit panel. “Furthermore, safety concerns are a typical policy consideration we identify when applying the discretionary-function exception.”