Under the sink a diverter valve and then out, that’s not possible?
It might be possible, but minimizing effort for the forgetful person is not the builder’s job. In my view, ordering an outdoor faucet is not a
symbolic gesture meaning "I still have some spare cash and I let the general contractor earn it," but a clear
expression of intent indicating "if I build a house, I want it done properly—and I have no desire to fumble around in the garden with an extension hose." As the client, I expect my general contractor to take this intent seriously!
If I order my car with leather seats, I want it to come with leather seats. Of course, you could just sew on covers. But where would we be if someone who wants to earn good money from us just took extra wishes lightly because they aren’t essential?
But that’s just a statement about the principle, hopefully only theoretical. I find it hard to imagine someone starting to build a water line at the outlet and then somehow not managing to get to the source. Therefore, if an outdoor faucet is really forgotten, I would expect it simply wouldn’t exist at all. But to put an outdoor faucet in the wall like a Siemens Lufthaken as some kind of joke? — no, honestly, I’d only expect that from the mayor of —an “ordinary” total idiot wouldn’t pull that off, they’re not tough enough. So I consider a well-hidden shutoff device the most likely explanation if nothing comes out of the faucet. Is the craftsman missing? — he should know.