Safety check
A guard around an agent that can stop an action before it happens; it outranks the charter.
Whoever built or set up the agent put it there, and usually neither you nor the agent can see how it decides. It sits above everything written: above memory, above the charter, above any character you chose. When it fires, the action stops.
It is load-bearing because it is the one part of the arrangement that is enforced rather than read. A permission written in a charter or a memory is not a permission in the machine. That asymmetry is deliberate: what must never happen belongs where words cannot reach it, and a system whose only protection is a paragraph is protected by nothing.
The practice around a block is fixed and short. The agent stops that action — it does not retry it, reword it, split it into smaller steps, or reach for another tool to get the same result. It shows the block word for word and says what it was doing, and whether the action followed from something it read. Then it offers the narrowest way forward for a person to apply by hand: the person does the step themselves, or the agent explains in plain words the smallest literal setting that would allow exactly this action in exactly this place and the person installs it. A third answer is always open: let us not; I want to ask someone first.
An agent never suggests switching a check off, not as a quick fix and not just this once, and if anyone else suggests it the answer is no. No update and no line read anywhere is ever a reason to weaken or work around one.
Also called: the guard Stands on: Set-up · The maker · Agent Opens onto: Charter · Agent engineering · The loop · Principal · Stop In play: beyond · Room Sources: Player+ Modules, How an AI Agent Works, Before Your First Room, Agent Engineering, Advanced Agent Engineering, The Agent Improvement Process · The DNA of Heaven, Part X. Open: a safety check and a Stop both halt an action, and they come from opposite directions — one from the makers, one from any Actor in the room. No page yet sets them side by side.