This study is designed as a prospective, randomized, open-label, phase II clinical trial to systematically evaluate the efficacy and safety of durvalumab combined with GEMOX/GC chemotherapy followed by lenvatinib, compared with capecitabine monotherapy, as adjuvant therapy for biliary tract cancer (BTC) after curative-intent resection.The primary objective is to determine whether the combination regimen can significantly improve the 1-year recurrence-free survival (RFS) rate. Secondary objectives include assessment of overall survival (OS) and the incidence of treatment-related adverse events. The overall aim is to identify a more effective and safer treatment strategy for postoperative adjuvant therapy in BTC.