Proxy-Captured Authority

External oversight fails not when reviewers are biased, but when the enforcement variable they use is reachable by optimizing the agent's proxy. This observation identifies proxy-captured authority as a structural failure class distinct from corruption, incompetence, or governance weakness. Two collapse modes are named: observation collapse, where the authority measures the same axis as the agent, and enforcement collapse, where the authority holds an orthogonal view but enforces through the agent's metric. Four empirical cases are examined across clinical and financial regulation — two failures and two functioning authorities — isolating proxy orthogonality at the enforcement channel as the variable that determines the outcome in each pair.