carwreck.com: around Boston harbor...
broadband!
It's back. I'm not sure how or why but I think I was escalated up throught AT&T tech support enough that some engineers went and figured out what was going on. It was definitely on their end. I was told that went a "Trouble Tracker" ticket is created for strange problems, they then send engineers to look into it. The engineers never enter explanations for the cause of the problem, they simply close the ticket. So I will never really know what was going on.
In any case, I have fast Internet again.