Ted Cruz isn’t giving up. While Donald Trump dispatches three advisers to Texas’s convention in Dallas this week and makes a pitch for party unity, his team will be running up against a Cruz operation that is still maneuvering to stuff the state’s delegation with allies the senator could call on to snub the presumptive nominee. “We have a busy weekend planned,” said a source familiar with the Cruz campaign’s plans. Cruz is scheduled to deliver an address at the Texas convention after a week of hinting he could jump back into the presidential contest and urging activists to thwart...