When an agent writes the code, you stop reading every line. You can pretend otherwise for a while, but on any real codebase you end up skimming a 600 line diff and approving it because nothing jumped out. Nothing jumping out is not the same as nothing being wrong. Documentation and a well tended CLAUDE.md only take you so far. The longer an agent runs, the more those instructions get crowded out of context and quietly forgotten. Instructions are advisory. Tooling is not.
