The agent worked. The architecture didn't. This failure mode won't show up in your eval suite. An AI architect builds a personal automation pipeline: an agent scouts trending content, pipes ideas into a chat thread, he reacts, things get logged. The agent did its job. It found the trends, wrote them down, and responded when he asked it to. He killed it anyway, and not over hallucination or token cost. He killed it because everything lived in "a flat scroll of messages. No structure, no...