A 64-year-old man with a 10-year history of type 2 diabetes and a prior anterior ST-elevation myocardial infarction presents for follow-up. He takes metformin, ramipril, a beta blocker, and a high-intensity statin. His HbA1c is 8.4%, eGFR is 65 mL/min/1.73 m², and he has no contraindications to additional therapy. Which agent should be added to best reduce his risk of further cardiovascular events?