A 58-year-old man from rural India presents with a 3-day history of colicky abdominal pain, abdominal distension, and absolute constipation. On examination, his abdomen is distended with visible peristaltic waves. Bowel sounds are high-pitched and tinkling. Plain abdominal X-ray shows multiple dilated small bowel loops with air–fluid levels in a "staircase" pattern, and the large bowel is collapsed. What is the most likely diagnosis?