There is without a doubt a variation of this prompt you can pre-test to successfully bait the LLM into exfiltrating almost any data on the user's machine/connected accounts.
That explains why you would want to go out and buy a mac mini... To isolate the dang thing. But the mini would ostensibly still be connected to your home network. Opening you up to a breach/spill over onto other connected devices. And even in isolation, a prompt could include code that you wanted the agent to run which could open a back door for anyone to get into the device.
Am I crazy? What protections are there against this?
Nothing that will work. This thing relies on having access to all three parts of the "lethal trifecta" - access to your data, access to untrusted text, and the ability to communicate on the network. What's more, it's set up for unattended usage, so you don't even get a chance to review what it's doing before the damage is done.