Thanks sebgl -- apparently I was using containerd for the runtime after-all -- I thought I blew that node away. Your link eventually got me to the solution:
version = 2
[plugins]
[plugins."io.containerd.grpc.v1.cri"]
[plugins."io.containerd.grpc.v1.cri".containerd]
[plugins."io.containerd.grpc.v1.cri".containerd.runtimes]
[plugins."io.containerd.grpc.v1.cri".containerd.runtimes.runc]
runtime_type = "io.containerd.runc.v1"
[plugins."io.containerd.grpc.v1.cri".containerd.runtimes.runc.options]
SystemdCgroup = true
for /etc/containerd/config.toml
Oddly, the instructions for creating the containerd configuration file here (Container runtimes | Kubernetes) made a configuration file that I couldn't just edit and inline the change above -- I had to completely replace the file with just the contents above for this to start working.