A self-healing test suite: CircleCI runs Stryker mutation testing on every push, and when mutants survive, the pipeline hands the surviving mutants to a CircleCI Chunk agent that writes the missing tests and opens a PR. A human reviews and merges; the next run is green.

push to main
   └─ install ─ unit-tests
            └─ mutation-tests        Stryker, JSON report -> score, prompt.txt, REMEDIATE
                  ├─ gate            re-scores; RED while mutants survive
                  └─ remediate       score < 70% -> triggers a Chunk agent task
                                        └─ Chunk agent writes killing tests, opens PR
                                              └─ PR gate must hit 100% -> human merges
                                                    └─ next main run: green

• src/ — four small, pure modules (age, numbers, strings, validation). Every mutant Stryker generates for them is killable, so 100% is a fair bar.
• test/ — starts deliberately weak: happy-path assertions only. Mutation score 46.97%.
• scripts/survivors.mjs — turns Stryker's mutation.json into the loop artifacts: a score file, a prompt.txt task brief for the agent, and a REMEDIATE flag.
• .circleci/config.yml — the four-job loop. mutation-tests is failure-safe (it can never strand the loop); gate is the tamper-resistant scoring authority (re-scores with CI-supplied arguments and rejects PRs that touch anything but test/).
• agents.md — standing instructions for the Chunk agent.

npm ci
npm test          # 15 green tests
npm run mutation  # score 46.97%, exit 1 — the weak suite caught red-handed

See RUNBOOK.md for the one-time CircleCI/Chunk wiring.