By Omar Faruk and Max Bearak MOGADISHU, Somalia — The calls from an unknown number had been coming for weeks, but Osman, a household-goods trader in the Somali capital’s largest market, disregarded them — until he got the text message. “Will you pick up our call? Yes or no. This is the mujahideen,” it said. The mujahideen, the Islamist...
