Thanks,Samuel B.
I think I’ve already done that (I created a sidebar-plain.php based on sidebar.php and figured out how to call it conditionally from psge.php), but the new sidebar-plain.php is the one I’ve stripped down to nothing but the dynamic_sidebar invocation so it’s a dead end for me since I can’t figure out how to manipulate that without going far deeper into the weeds than is wise for my lack of knowledge.