Upgrade from Catalina to Big Sur from command-line?

How can I fully automate an upgrade from Catalina to Big Sur on our 300 Mac CI machines?

I already know that there is a manual way to upgrade to Big Sur using a GUI app (https://support.apple.com/en-us/HT201475).

I can download the "Install macOS Big Sur" application into the /Applications folder in an automated way, that's not a problem.

I can also even have the install begin and auto-accept the license, etc using this command:

sudo "/Applications/Install macOS Big Sur.app/Contents/Resources/startosinstall" --agreetolicense --forcequitapps --nointeraction

However, the processes that I care about (buildkite-agent) don't start automatically until I perform a login through the standard login screen over VNC. After logging in through VNC (using the above command) there is a flurry of activity for a couple minutes and then the computer is back working 100%

Unfortunately, a login with a standard SSH connection will work to kick off the rest of the post-upgrade (or mid-upgrade as it appears) work.