Thanks to both you and joemike for your responses.
This is a bizarre one that I hope will be the real final chapter of this saga
Reflecting on your posts (joemike’s linked discussion isn't analogous.), I realized that LabTick’s unvarying “Avg Energy Impact” of ~20 might be my culprit, quit it, restarted, and learned that it was not only not guilty, it wasn't even necessary any longer. (One less 3rd party utility!
And then I remembered NoSleep, which I’d have sworn I’d trashed 3 weeks ago but had, much to my chagrin, found on my Pref Panes list just a few days ago:
- I realized that I had trashed only those of its components that EasyFind permitted, not those that required a password.
- Although it’s not on my list of Login Items - the option is grayed out in its pref pane - it opens automatically when I log in, anyhow...somehow.
- Its obligatory menulet is missing from my menu bar.
- It doesn't show as an active process in Activity Monitor!
- It doesn’t open in safe mode.
Ideally, I’d have stayed in safe mode until I was certain that No Sleep is my culprit, but (as opposed to my earlier misstatement) powerd’s % CPU does
get reset back to 0.00-0.01 after a restart and takes waaay longer than I can stand to be in safe mode to ramp up to a noticeably unusual level.
At this point, though, I’m ready to hang my hat on its being my culprit.
It looks like it has somehow gotten its hooks into powerd such that both it and Activity Monitor run amok when AM tries to read it, but only
then. (“top” shows 0.00-0.01% $ CPU for powerd with AM quit.)
My real answer, then, is apparently to get rid of NS (which might require a nuke & pave), but I like my current hybrid functionality(*), and quitting powerd every once in a while is a small price to pay for it, so…
(*) NoSleep is supposed to keep a laptop awake indefinitely while its lid is shut, but it now does so only until Energy Saver’s sleep setting overrides it, and it can still be toggled on/off in its pref pane.
Afterthought: I'm going to try to avoid restarting for a while to see how long it takes powerd to ramp up to the 75% CPU point it was at when I first posted, and then I'll boot into safe mode when I'm leaving my house for a while and make sure that my issue doesn't follow me...hopefully nail down my theory.