The "does every session need this" filter for AGENTS.md is the most transferable rule, a hard line-count ceiling forces real discipline instead of "just one more exception" creeping in forever.
"Don't turn one failure into a universal law" is the sharper insight. Requiring both a regression case (rejects the bad example) and a positive case (still passes valid ones) is what stops an overbroad fix like "never use mocks" from replacing a narrower real problem.
Self-review not being independent, even when the agent inspects its own diff, is worth remembering, it already committed to the assumptions behind the output, so grading its own homework isn't structurally the same as a reviewer with no stake in it.