Well, I did put the battery back in this afternoon and fired it up and was able to shut it down. Went flying and took some photos and everything seems to work as it always has. Problem gone. Resolution???? No idea. But apparently I can take out...
My Air 3 did that once about a year ago, and after trying the standard shutdown procedure several times with no success, I pulled the battery out. Left it out maybe 15 seconds or so, then put it back in the drone and everything behaved normally...