Wall Street just had its best day in nearly a year over a rumor

As the bell rang out over the New York Stock Exchange on Tuesday afternoon, it was an unusually beautiful day: 71 degrees, sun shining on the faces of people swarming through the city. After the brutal cold of winter, it felt like something of a miracle.

The markets had spent the day chasing one of their own.

Iran’s official news agency reported an unconfirmed phone call between President Masoud Pezeshkian and the European Council president, where Pezeshkian said Iran had the...