The exclusion of Europe, Russia, and China from the contemporary iteration of Washington-Tehran deliberations signifies a profound structural transformation in the architecture of international conflict management. For nearly two decades, the Iranian nuclear file stood as the quintessential archetype of robust, institutionalized multilateralism. Today, however, we are witnessing a fundamental recalibration of the systemic logic governing this issue. The transition from a hyper-pluralistic diplomatic theater to a strictly restricted, bilateral channel is not merely an incidental adjustment of the roster of participants; rather, it reflects a shared cognitive shift within both Washington and Tehran....