My devices always run as root.
However, I have discovered that "Clipboard Change" does indeed work, at least in *some* cases. With certain apps, such as the Textra SMS client, selecting and copying text doesn't trigger that context, and this happens to be where I was first testing "Clipboard Change". However, I now realize that when selecting and copying text in a number of other apps, the "Clipboard Change" context does indeed get triggered.
I guess it's simply the case that certain apps don't do copy-and-paste in "official" Android manners.
Thank you for your help.