A 28-year-old man is brought to the emergency department 20 minutes after a stab wound to the left chest at the 5th intercostal space, mid-axillary line. He is alert, blood pressure 110/70 mmHg, heart rate 102/min, respiratory rate 26/min, and oxygen saturation 96% on room air. Breath sounds are diminished on the left. Chest X-ray shows a moderate left hemothorax with no mediastinal shift. What is the most appropriate next step in management?