Robert Maher came out and looked at the sewer problem, but couldn't do anything about it. Went out and bought 100ft snake and attempted to ream out pipe myself (spent pretty much the entire day on it; got no other work done). Results uncertain but not satisfactory.
Insane, insane day. Saturday PM the sewer line stopped up completely. Handyman who came around this morning couldn't fix it. Spent all day (and $400 on eqpt.) in the basement trying to fix it myself... but for all I can tell it's still clogged, tho the snake goes all the way in (100 feet). Maybe the line tilts up a little? Too tired to test. We're essentially on a whole-house chamberpot until it's fixed.
(in a comment, someone asks about the possibility of roots)
Actually, I don't think it's roots; what's coming up is pieces of non-flushable disposable wipe. My theory -- which is proving difficult to prove -- is that I've actually managed to snake out the obstruction, but there is a slight uphill angle to the pipe as it goes out to the street -- so stuff gets pushed back into the cleanout (which is right at that same level).
I think we're gonna get a plumber who has a drain endoscope to see what's going on, because I can't think of any good way of testing that theory without risking having to drain the pipes all over again (which took forever and I haven't the energy).