When a defendant enters a conditional guilty plea, reserving the right to appeal an adverse decision on a motion to suppress, what harmless-error standard governs the determination of whether the defendant 'prevails on appeal' under Federal Rule of Criminal Procedure 11(a)(2)?

QUESTION PRESENTED When a defendant enters a conditional guilty plea, reserving the right to appeal an adverse decision on a motion to suppress, what harmless-error standard governs the determination of whether the defendant “prevails on appeal” under Federal Rule of Criminal Procedure 11(a)(2)?