In Vienna this week, the annual gathering of the world's nuclear watchdog convened without one of its most consequential figures — Iran's atomic energy chief, Mohammad Eslami, barred from attending after the United States blocked Austria's request for a travel ban exemption. The episode distills a larger tension: between the formal architecture of international diplomacy, which presupposes a shared table, and the coercive instruments of sanctions law, which can quietly remove a chair. At a moment when Washington signals openness to engagement with Tehran, the simultaneous exclusion of Iran's n