A 72-year-old woman with a history of hypertension (on atenolol 50 mg daily) and recurrent urinary tract infections presents with a 3-day history of fever, dysuria, and confusion. On examination, she is febrile (38.5°C), hypotensive (92/58 mmHg), and tachycardic (118/min). Laboratory investigations reveal: serum potassium 6.9 mEq/L, sodium 128 mEq/L, creatinine 2.8 mg/dL (baseline 1.0), blood glucose 420 mg/dL, arterial pH 7.18, HCO₃⁻ 12 mEq/L, and positive blood cultures. ECG shows peaked T waves. What is the PRIMARY mechanism of hyperkalemia in this patient?