A 28-year-old woman presents to the emergency department 20 minutes after eating peanuts at a restaurant. She complains of severe itching in her mouth and throat, followed by facial angioedema and stridor. On examination, her blood pressure is 88/54 mmHg, heart rate 118/min, and she has urticarial rash over her trunk. Serum tryptase level is elevated at 8.5 ng/mL (normal <1 ng/mL). Which of the following best explains the pathophysiology of her acute symptoms?