This is a prospective, single-arm, exploratory clinical study designed to evaluate the efficacy and safety of retlirafusp alfa plus CAPOX as conversion therapy in patients with potentially resectable gastric or gastroesophageal junction adenocarcinoma. Eligible participants will receive preoperative retlirafusp alfa in combination with capecitabine and oxaliplatin. Patients who achieve complete response or partial response and are considered suitable for R0 resection after multidisciplinary team assessment will undergo radical surgery. The primary outcome is R0 resection rate.