The lesson: I went to see the doctor in November when rest was not working. I futzed around with the MRI and did not get in until early February. I'll be getting surgery in mid-March. Had I moved at the appropriate pace, I might have had surgery before the holiday and been back in the swing of pain-free running by now.
On the other hand, four-or-so months off and an almost certainty of a marathon-free year can't be all bad.
NB: This explains my staccato of "I ran pain free!"/"I can't walk!" Apparently meniscus tears hurt or not more or less at random.