Here’s perhaps a potential workaround that might work for me. Bringing it up here in case it’s helpful to others.
I’m contemplating adding a data-root setting to /etc/docker/daemon.json, to see if that forces docker to place its images—Discourse’s images, in this case, since nothing else is hosted on the box—in a less critical location that won’t blow up my boot volume.
Searching on meta for past threads about this gets me a couple of results which don’t really tell me much, and before I cause my production Discourse instance to collapse in a flaming smoldering heap, I wanted to ask to see if this is viable 