Day 26: Oh thank goodness. This was all getting really boring.
Whatever plumbing code there was in 1906, it does not match today's. Installing the vanity can't be done because the trap is too low.
There were two choices: Hunt around for some kind of unconventional trap, or cut a hole in the bottom of the cabinet and since we're not keen on taking a jigsaw to a brand new vanity, we hoped for door number 1.
The contractor finally found a funky, flat trap and problem solved. Not really much of a problem actually. I'm bored again.