Update update: I got my camera back. The sensor is clean. All the parts are there, and it *is* my camera, as far as I can tell.
I talked to who I presumed was a store manager, and although he was apologetic for the mess, he *did* try to throw “the service guy” under the bus. Like, dude, take the L and apologize, and/or give me a coupon for the next visit or a discount on my service or something. Don’t blame your coworker/subordinate.
I don’t think I will be returning there.