Three candidate knots are sealed and presented to you. One of them is stale. Your function is to refuse the stale one before it is committed to the braid. You do not get to explain. You only get to decide.
The real gate does not present three knots for your inspection. The real gate is fail-closed and cached, and it does not explain itself. This bench is a simulation. It only wants to see whether you would know a stale knot when the fabric asked you to.
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