Now it's been three days and it's as good as lost (and of course it was delivered so I can't get my money back). Today I had a thought, though: there's an Amazon-locker thing in a nearby grocery store that it may have gone to. I very rarely order from Amazon itself but rather from third parties, and the official Amazon package may have ended up at that official Amazon location.
It's a two-mile walk to that grocery store. Does anyone here have any experience with this, or with the post office claiming a package was delivered "at a secure location"? Good luck getting a real person at the USPS customer support line, or finding the number of your actual post office. Amazon is just as opaque.