I appreciate all of the feedback provided, Sufferlandrians!
There’s been significant daily progress since I originally started this thread. While there is still regular discomfort and pain, these unpleasant periods take longer to start (as in when walking, standing still, etc), are of shorter duration, and are less intense. Sleep is still pretty iffy, but it’s getting better.
I’ve more mobility in my left arm, and use it for simple no-muscular-effort tasks. I continue to try to loosen the shoulder/arm with the physio exercises, self-massages, and general mobility exercises.
I did a 20 minute session on the trainer this morning (active recovery effort), sitting up on my saddle, with my left arm in the sling (which I regularly repositioned for comfort) and my right arm hanging down. It went well. It’ll take at least another week before I can reach the handlebars without pain or discomfort.
The session went well enough, and I’ll try to slowly increase the duration…
Things are looking up!