Are there any packages that build OCI / Docker images without Docker? Can the Docker package be configured to use podman, buildah or anything else?

podman usually ships a shim package, like podman-docker on Ubuntu.

Won't help: the Docker package is using the API, not the CLI. It's connecting to the Docker daemon's port. Which podman doesn't provide (and indeed, that's the entire purpose of podman, to avoid running a root service).

It does.

I guess I must have been using a wrong version. I didn't even have a podman machine running, and qemu wasn't installed. But podman was doing everything I needed.. until this point. Anyway, thanks to your links, I've got podman machine running. However, the socket is still not exposed. I read the socket activation link, but there's nothing in there about Windows/WSL. The startup messages don't look like the ones I see at https://github.com/containers/podman/blob/main/docs/tutorials/podman-for-windows.md, either.

For socket activation (or running a daemon) - you need to enable / start it manually. Maybe even write own systemd unit (depending on the distro you use)

I tried that, but was still getting the couldn't-find-the-pipe error. Back at the computer now, will look into it more.