I finally got the cooktop and oven removed from their nooks in the cabinets and countertop and got a good look behind there.  There is, in fact, a gas line back there, in the middle of a hole the builders helpfully hammered out of the drywall.  So now I’m waiting for a call back from a plumber to schedule him to come out and install a cutoff valve on that line.  After that I’m going to have to remove a couple boards that were used to make the shelf for the oven, cut the countertop (it’s getting replaced anyways), and go out and buy a gas range.  I’m probably going to have the carpenter give me an estimate on installing a new countertop while he’s out here giving me estimates on some other work.