Is a defendant's failure to object at sentencing waived in the Court of Appeal?

4 Citing our decision in United States v. Flores-Payon, 942 F.2d 556 (9th Cir.1991), the government argues that a claim of government breach of a plea agreement is waived by failure to object at sentencing. Flores-Payon, in which the defendant initially raised his claim before the court of appeals, is a straightforward application of "the general rule against review on appeal of issues not raised below." Id. at 558. Flores-Payon does not address the appropriateness of collateral review, in which the district court, the traditional locus for resolution of factual disputes, has the first opportunity to pass on the claim. Cf. id. at 559 (distinguishing cases in which district court "had an opportunity to develop a record following the defendant's claim of breach, either in the original proceeding or on collateral review"). Thus, Flores-Payon does not render claims of plea-agreement breach comparable to other constitutional claims, subject to express statutory waiver provisions, for purposes of Frady and collateral review.