This is an investigator-initiated, prospective, open-label exploratory clinical study designed to evaluate the safety and preliminary efficacy of GoFast CD19 CAR T-cell therapy in adult patients with recurrent or refractory B-cell lymphoma. Eligible patients will undergo screening, baseline assessment, peripheral blood or leukapheresis collection, lymphodepleting chemotherapy, and intravenous infusion of GoFast CD19 CAR T cells. The study plans to enroll 9 participants using a sequential dose-escalation design. The primary outcome is objective response rate, and secondary outcomes include complete remission rate, overall survival, progression-related survival outcomes, duration of response, MRD negativity, and adverse events.