Whether a defendant can waive the right to appeal his sentence before the right has accrued

QUESTIONS PRESENTED FOR REVIEW 1. Whether a defendant, consistent with the Due Process Clause, can waive the right to appeal his sentence knowingly when his purported waiver occurs before the right has accrued. 2. If such pre-accrual sentence-appeal waivers are constitutionally permissible, may a waiver in a written plea agreement be enforced when the district court failed to advise the defendant of the provision and failed to ensure that he understood its meaning and consequences.