Back to the orthopedist this morning to review MRI. He said it didn't show anything interesting except a thickened capsule (textbook frozen shoulder) and a few stray labrum fibers which are not unusual. So I just keep using heat, no PT or stretching yet, and follow up in 6 weeks.
I asked whether sudden movements that hurt (didn't mention stumbling in the forest) were likely to cause a setback, he said probably not at this stage, that is more of an issue early on. Still worth minimizing I guess.