Set up BuildKit on this VM by following the exe.dev recipe at https://exe.dev/deploy/docker-builder.md from top to bottom.

The recipe's example VM name is my-builder. This VM's name is the output of `hostname`: use it wherever the recipe writes my-builder. Skip the step that creates the VM; you are on it.

This recipe needs a 100GB disk, and a new VM's may be smaller. Before you install anything, run `df -h /`. If its size is under 90G, stop and ask me to grow the disk, either with this link: https://exe.dev/suggest?command=resize%20my-builder%20--disk%3D100GB or, on my computer, with `ssh exe.dev resize my-builder --disk=100GB`. When I say it's done, run `sudo resize2fs "$(findmnt -no SOURCE /)"`, check `df -h /` again, and carry on.

You are done when all of these are true. Check each one yourself:
- BuildKit running as the buildkit systemd service, started at boot
- A socket that only the buildkit group can use, with exedev in it
- Garbage collection that keeps the cache under 60% of the disk, leaves 20% free, and keeps cache mounts for two weeks
- Builds for linux/amd64 natively and linux/arm64 through BuildKit's own QEMU

Read the whole recipe, but run only "Set up the builder by hand",
skipping VM creation: fetch and run builder-setup.sh. Everything about
docker buildx, ~/.ssh/config, CI, and sharing runs on the owner's
computer or is the owner's choice. Don't install or configure Docker,
don't open BuildKit on TCP, and don't add users or SSH keys unless the
owner asks. Verify: buildkit.service is enabled and active;
`sudo -iu exedev buildctl debug workers` lists one worker; and
`sudo buildctl debug workers -v` shows the five GC rules. Finish with
this VM's CPUs, memory, and free disk (nproc, free -h, df -h /), the
`ssh exe.dev resize` command from "Size it" with this VM's name, and the
commands for the owner's computer.

Finish with the URLs I should open and these commands, which only I can run, from my own computer (with this VM's name in them):
  docker buildx create --name exe --driver remote ssh://my-builder.exe.xyz
  docker buildx inspect exe --bootstrap