The killing of Iran’s Supreme Leader Ayatollah Ali Khamenei in the latest US-Israeli strikes on the country has triggered not only a leadership vacuum but also a high-stakes test of whether the Islamic Republic’s system can endure without the man who dominated it for nearly four decades. Analysts said the immediate signs point less to collapse than to hardening continuity, at least for now, as security institutions close ranks, the battlefield expands and signs of internal rupture remain...