The 10-inch, 3G-enabled tablet, akin to a jumbo iPod touch, is the latest brainchild of chief executive Steve Jobs. That distinction, as insiders will tell you, carries its share of baggage. Under the critical eye of Jobs, contours must be precise, each pixel of the interface has to match a particular vision, and there can be no fault — no matter how slight — or it’s back to the drawing board.