Well...overnight, the caches must have emptied—whether from the browser or from the system, I don't know. There is no longer the error, and the rendered code of the public pages (viewed through the web inspector) now shows the sourceMappingURL=plugins_public/marka/marka.min.js.map change I made to the mark.min.js file. (Yes, I made a typo in my original post above, leaving off the suffix, .map, when describing my fix.) I have no idea if the change will break some other pages, but for now it seems to have solved the 404 errors described above for the marka.min.js.map file.