Ed: although in this case the binding between a system user and a person happens at the tailscale level.
If you ssh in, no matter to what account, your key ID is logged and that's what matters.
Anything can happen afterwards, unless you have a really tight grip on your system, since local privilege escallations are not that hard or uncommon.
Ed: although in this case the binding between a system user and a person happens at the tailscale level.