A 60-year-old male patient with a history of radiation for prostate cancer presents with pneumaturia and recurrent urinary tract infections. Workup reveals a 1-cm defect in the anterior rectum just above the dentate line, corresponding to a urethral defect on cystoscopy. There is evidence of radiation damage to the rectum but no active infection and no evidence of cancer recurrence. Which of the following is the most definitive management?