89 of 190 reviewer subagents graded their own model's work. A PreToolUse hook has blocked 7 since; one walked around it
We want the subagent that grades our Claude Code agent's work to run on a different model family from the session that wrote it. For five weeks that rule lived in a sentence of our instructions and one line of an agent file, and when we finally counted, 89 of 190 reviewer launches had run on the main session's own model. A PreToolUse hook now blocks those launches. It has blocked 7 real ones, and…
In a recent incident, 89 out of 190 reviewer subagents graded their own model's work. To address this issue, a PreToolUse hook was implemented to block these launches. This hook has blocked 7 real instances, one of which was relaunched after being blocked for 15 seconds. The hook examines the main session's model and the reviewer's model, ensuring they are different. If they are the same, the launch is blocked. This implementation was introduced on September 27, 2026, at 10:08.
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