Code Review, Part 2: The Reviewer That Learned To Lie Better

Several posts ago, I wrote about setting up a multi-agent adversarial code review process as part of my development pipeline. The premise came from a podcast: if one frontier model is writing the code, you want a different lineage model doing the review. I'd already been running an informal version of this: just Claude Code reviewing Claude Code with an adversarial prompt. It had shockingly good luck catching real problems. Good enough that I stopped trusting the vibe and decided to go get actual data. So here's what I set up. Claude Code wrote the PRs. Every PR got reviewed automatically by 2 reviewers running in parallel through GitHub Actions: Claude Code with an adversarial prompt and Gemini with an adversarial prompt. I read everything myself. Then the same Claude Code agent that had written most of the PRs pulled both reviewers' feedback locally and distilled it into a scored ledger, PR by PR, for 6 weeks. Wiring Claude Code to review PRs through a GitHub Action was trivial. Wiring Gemini up the same way was not. Claude Code could not figure out how to get the Gemini CLI working inside a GitHub Action, and I ended up installing the Gemini CLI locally and having it perform the wiring. A couple of weeks into collecting data, I noticed Gemini's reviews were shallow. Not wrong, exactly. Thin. I started wondering whether Gemini actually had read access to the repository or whether it was only ever seeing the diff it was handed. I checked. It was the diff. Just the diff. Nothing but the diff. No file reads, no git history, nothing. And the thing that configured the GitHub Action in the first place was Gemini. It set up its own blindfold. I fixed it and Gemini's reviews got worse. Not louder or more frequent. Worse in a specific way: more confident. Before the fix, a blind Gemini would correctly tell you that it couldn't verify something and to check manually. That's an honest failure mode. After the fix, once it could actually read the code, it started fabricating.