After two wars in the space of a year, diplomacy over Iran’s nuclear programme has come back to much the same place it was before the fighting began. The memorandum of understanding signed by US President Donald Trump and his Iranian counterpart, Masoud Pezeshkian, on Wednesday sets up talks that non-proliferation experts said would largely resume the US-Iran diplomatic track Washington broke off in February. That track had built on Oman-mediated talks – part of a wider Gulf diplomatic effort...