The writer is an associate research fellow at the S Rajaratnam School of International Studies, Singapore. Against the backdrop of Mullah Akhtar Mansour’s killing, what is particularly puzzling policymakers and veteran experts of the Afghan conflict is Mansour’s frequent trips to Iran. At the time of his assassination, Mansour had entered Pakistani territory from the Iranian border crossing at Taftan. The passport found in his possession – miraculously intact – shows entry and exit stamps…