AI Cited a URL That Didn't Contain the Claim. I Built the Tooling to Measure How Often

Citation hallucination has four distinct failure modes — fabricated URLs, retrieve-then-misquote, URL substitution, and anchor-text drift. They look the same in the response but they have different causes and different fixes. A field report on measuring citation faithfulness in production. The first time I caught it, I assumed I was misreading the response. The user query was about a specific competitor's pricing. The model produced a confident, well-structured answer with three inline citations