Part I — What it is & why

Imagine hiring a brilliant, tireless worker who follows written instructions exactly — even a note a stranger sneaks onto the workbench. That's an AI agent. To keep a bad instruction from spilling out, you can put the worker in a locked room: at minimum it can only write on its own bench. Ask for the stronger "curtained" room and it also can't read your private files; and the strongest lock (on Linux) also cuts the phone line. (Which protections you get depends on how much you ask for — see Part IV.)

Two things do the guarding: the locked room (what the worker can touch and reach) and a guard by the door who can shout "stop!" at a few obviously dangerous actions.

Important, and easy to forget: this room is only for the worker who builds your product. It is not inside the product you deliver — the thing you ship to your own customers needs its own protections.

Plain-language ceiling #1 — the room now comes with a lock fitted, but you still have to turn the key. By default the worker's room comes with a lock provided — but the lock isn't turned until you wire it in, so nothing is actually held back yet, and the guard by the door still says "if in doubt, allow" unless you deliberately ask for the locked room. Set the dial to "open" if you'd rather no lock be fitted at all.