A proposed agreement being discussed between Iran and Oman could hand Tehran a significant role in overseeing ships entering the Persian Gulf through the Strait of Hormuz, according to a senior Iranian source and two regional officials familiar with the negotiations. If implemented, the arrangement would mark one of the most consequential changes to the management of one of the world’s busiest energy trade routes, although officials involved in the talks cautioned that key issues remain unresolved and that no final agreement has yet been reached.