Kubernetes sounds like overkill, but I've been running microk8s for few standalone servers. This feels a pretty good match when working with agents. Codex can manage the cluster also over ssh, schedule new pods, check statuses, logs etc.
I think k8s is a great choice today specially when you can plug it into Gitlab and have a control plane for your clusters in the same place where your code lives.
K3s is also pretty nice for a minimal setup
Haven't used it in a while but this thing is also interesting--it supports a bunch of different ways to spin up k8s https://github.com/tilt-dev/ctlptl