In the long and turbulent story of Persian Gulf rivalry, a rare diplomatic opening between Saudi Arabia and Iran has been quietly closed — at least for now. Talks planned for Oman, a nation that has long served as a quiet bridge between adversaries, were called off by Riyadh as Houthi and Iraqi militia threats pressed in from the margins. The postponement is a reminder that diplomacy between great rivals is always fragile, and that the proxies of conflict often speak louder than the envoys of peace.