But why does this need any new legislation? It doesn’t matter if the agent is air gapped or not, as long as it doesn’t do illegal stuff. Hacking is illegal unless you were tasked to do so for security reasons by the target.

As long as judges don’t start treating agents as independent persons, their operator should be on the hook for everything they do. So if you fail to safeguard your agent, and your agent performs an illegal action, you are liable. That should be deterrence enough.