to exercise discretion, it must be presumed that the agent’s acts are grounded in policy when exercising that discretion.”). Hart does not cite, and we cannot find, any law or facts rebutting this presumption. We readily conclude a federal law enforcement officer’s on-the-spot decisions concerning how to effectuate an arrest — including how best to restrain, supervise, control or trust an arrestee — fall within the discretionary function exception to the FTCA absent a specific mandatory directive to the contrary. See, e.g., Dykstra, 140 F.3d at 796 (“We have no difficulty in concluding that the discretionary function exception applies to the correctional officer’s decision not to place Dykstra in protective custody or to take other protective action.”); Deuser, 139 F.3d at 1195-96 (<HOLDING>); Mesa v. United States, 123 F.3d 1435, 1438
recognizing a discretionary function exception to that waiver holding the manner in which federal law enforcement agents investigated a suspect and execut ed an arrest warrant fell within the discretionary function exception to the ftca holding a park rangers decision to terminate an arrest falls within the discretionary function exception to the ftca because such decision was the classic example of conduct grounded in policy holding that the discretionary function exception may apply in the absence of a conscious decision  holding that decision to operate lighthouse is discretionary decision while failure to maintain lighthouse is not within discretionary function exception