What builds up when nobody is looking.
Entropy
Agents copy what they find. Good and bad patterns alike spread with every run, so a repo nobody tidies gets less consistent, and faster than people alone would make it. No single change looks wrong. The drift shows up later.
More agents means more copying per day. The harm is that bad patterns become examples: the next agent finds them, sees that they pass, and copies them. A rule enforced by a machine is the only kind that works at that speed.
Say it to your agent
“Find every place we call fetch directly instead of apiClient. Add a lint rule that fails on it, naming apiClient in the error message. Fix the five oldest in this pull request, and list the rest.”