AI agents rarely fail in a clean, obvious way.
They do not always crash. They do not always throw an error. They do not always say, "I could not complete the task."
Sometimes they fail more quietly.
They give a confident answer with weak evidence. They complete the easy half of the task and skip the important half. They repeat the same tool call as if the previous result never happened. They drift away from the original goal one reasonable step at a time. And the most dangerous version: they say done when the task is not actually done.
That is what makes agent reliability so hard.
