I restarted the MBP and it hung with that spinning icon thing. But it has no power button so I did not know how to forcibly power it off. The touchbar was blank and was unresponsive to anything; the machine was hung and unusable with a blank screen, aside from that spinning icon thing.
I found this non-obvious solution at Apple (what would I have done without another Mac?!) in How to turn on or turn off your Mac:
MacBook Pro (15-inch, Late 2016) and MacBook Pro (13-inch, Late 2016, Four Thunderbolt 3 Ports): The power button is adjacent to the Touch Bar and integrated with the Touch ID sensor. Press Touch ID (power button) to turn on your Mac.
Not only is the touchbar completely blank when the machine is off (very confusing, where does one press and for how long, etc?!), the touchbar is one long strip, with no power button to be seen! Also, this advice says nothing about powering *off* the Mac, so I missed it at first, But then finally guessing that it meant power on or off, I tried it: pressing and holding the right side of the touchbar did power it off. I still cannot find any power key anywhere! No visual feedback, no tactile feedback, very poor explanation.
When this hang arose, this was all very confusing because there was just a blank touchbar. Nor is it even obvious where one should press on the touchbar, since the touchbar was totally blank. I still don’t know exactly where to press, even with the machine booted up—design insanity.
Once powered off, one has to close the lid and reopen it to boot thing up. Or presumably the touchbar thing works for power on, but its lack of visual or tactile feedback makes it all mysterious. One is just supposed to know to press in some magic spot? How is that better than a power key, which is self evident?
Requiring special knowledge for basic/key operations is poor design judgment.
Also, Apple has removed the startup sound, so there is no feeback that the dang thing is rebooting, until it actually does (update: enable the startup chime). Ditto for restart. Poor feedback again, because one cannot turn away for a moment: it is now required to stare at the computer to confirm if it is going to restart, or if it is going to hang. Nor is there any clue as to when it has started booting up: stare at the screen until it happens, whereas the startup sound was obvious auditory feedback.
Lack of feedback is poor design judgment.
The foregoing is not a criticism of the touchbar per se; I like the touchbar overall and the touchbar has potential for time-saving features.