Well, that was almost a disaster. I'm not too sure where most of the responsibility lies. Could be me, for not really understanding what I'm playing at. Could be the gitsync plugin for Grav, for allowing me to do stuff that I don't really understand. Whatever, although I was initially quite pleased with myself, that sweet satisfaction turned to ashes in my mouth this morning when I returned to the site to fix an error that had arisen in the meantime. Nothing, and I mean nothing, worked as it should. Almost five hours later, and it would have been much, much more if not for git, I'm back where I started before I embarked on this hubristic adventure.
I had help, most notably from Deleting your master branch by Matthew Brett. It wasn't the whole story, but it was enough to get me back on track. And from the Grav community, of course. Now that I am back where I want to be, I will resist the urge to tinker with my workflow for posting for a little longer.