Caustic Esophagitis — Zargar Grade IIIB

A 24-year-old woman presents to the emergency department 4 hours after suicidal ingestion of 200 mL of liquid drain cleaner (sodium hydroxide, pH > 12). She has severe retrosternal pain, odynophagia, drooling, and hoarseness. After airway intubation for protection, upper endoscopy is performed at 12 hours post-ingestion. The esophageal mucosa shows the finding marked **C** in the diagram. Based on this endoscopic finding and the Zargar grading system, which of the following is the most appropriate next step in management?