Later note: It proved simpler and cleaner to symlink /var/lib/docker to a location with lots of space on my spinning disk. Normally when I test this docker container, I want it to start from nothing (i.e. preserve no data from previous runs) so there's no advantage to mounting external storage.
After many iterations of build, run, watch jobs fail, figure out missing packages, tweak scripts, and round again, I have five jobs building successfully, and another four remain to be tested. I was running my docker instance with local data like this:
docker run --name teijenkins -p 8080:8080 -p 50000:50000 -v /var/jenkins_home tei-jenkins
but that was problematic because the image was exploding in size as it checked stuff out and built jobs, and I ran out of space on my SSD. I copied the contents of the /var/jenkins_home directory to my spinning disk and I'll be trying this instead:
docker run --name teijenkins -p 8080:8080 -p 50000:50000 -v /home/mholmes/WorkData/tei/jenkins_home:/var/jenkins_home jenkins
but I have to free up enough space to run the image in the first place. Working on that now.