Harness Evolve

Surfaces the upstream metaharness-darwin evolve CLI as a ruflo skill. The write layer that pairs with ADR-150's read layer (score / genome / mcp-scan / threat-model / oia-audit). Use when you have a harness whose readiness scores are flat and you want to discover which surface mutation moves them — without retraining the foundation model.

When to use

• A harness-score result is below target and you don't know which policy surface is responsible.
• You're seeding a harness for a new vertical and want to find a good starting configuration empirically rather than hand-tuning.
• You're comparing your hand-tuned harness against an evolved baseline (treat darwin's champion as the strawman).

When NOT to use

• For continuous background optimization. Darwin Mode is human-initiated. Wire it into CI for one-shot exploration, not for autonomous self-modification.
• For ruflo itself in CI. ADR-153 §5 explicitly rejects auto-evolving ruflo — the CI gate verifies graceful degradation, not convergence.

Algorithm

Implementation: scripts/evolve.mjs.

1. Validate args (--repo exists, caps on --generations ≤ 50, --children ≤ 20, --concurrency ≤ 8, sandbox/selection/mutator are known values).
2. Without --confirm: print plan + exit 0 (mirrors harness-mint safety convention; defense in depth over the upstream safety.ts checks).
3. With --confirm: shell to npx -y @metaharness/darwin@~0.8.0 metaharness-darwin evolve <repo> ... via the shared _darwin.mjs async helper. Per-generation progress is forwarded to stderr; final champion JSON is captured from stdout.
4. Compute timeout from generations × children × per-variant (per-variant ≈ 60s real, ≈ 2s mock). Caller may override with --timeout-ms.
5. Honor upstream exit code 99 — propagate as "safety-disqualified", do not remap. This is a designed-in tripwire (a variant tripped inspectVariant for secrets / shell-out / network / dynamic-eval). See ADR-153 §"Safety model".
6. Optional --alert-on-no-improvement: exit 1 when champion ≤ parent.

The seven mutation surfaces

One mutation per variant. Multi-surface mutations are not allowed (causal attribution stays clean).

Output

Reports land under <repo>/.metaharness/:

.metaharness/
  archive.json         # full lineage tree (sampling next gen draws from this)
  lineage.json         # parent→child edges only
  variants/<id>/       # per-variant code (kept for audit)
  runs/<id>/           # per-variant sandbox test output
  reports/winner.json  # final champion + score delta vs parent

Skill stdout = JSON {success, data: {champion, plan, durationMs, improved}} (plus data.diagnosis when --diagnose is passed — see below).

Failure diagnosis (--diagnose)

GEPA's key trick is natural-language failure diagnosis from execution traces feeding the next mutation — not just scalar fitness. --diagnose adds a modest slice of that: after the evolution completes, the losing / failed variants' transcripts are run through darwin's GEPA library ops (analyzeTranscript + classifyFailure, via the shared importGepa resolver in scripts/_darwin.mjs) and a diagnosis section is appended to the emitted JSON:

"diagnosis": {
  "available": true,
  "scope": "losing-variants",
  "variants": [
    { "id": "g1_v0", "transcripts": 2,
      "failureClasses": { "exploration-loop": 1, "edit-mechanics": 1 },
      "dominantClass": "exploration-loop" }
  ],
  "totals": { "exploration-loop": 1, "edit-mechanics": 1 }
}

Upstream shape caveats (verified against @metaharness/darwin@0.8.0):

• metaharness-darwin evolve --json prints a TEXT leaderboard — the stdout carries no JSON and no transcripts. Per-variant run records live at <repo>/.metaharness/runs/<id>.json.
• Those run records hold sandbox exec traces ({taskId, exitCode, stdout, stderr}), which are NOT GEPA {actionRaw, obs} transcripts. Diagnosis therefore uses GEPA-shaped transcripts when a run record embeds them (agent sandbox / future upstream), falls back to the champion's transcript, and otherwise emits diagnosis: {available: false, reason, traceSummary} where traceSummary is a mechanical per-variant tally (tasks / failed / timedOut / blockedActions).
• --diagnose NEVER fails the run — any internal error degrades to {available: false, reason: "diagnosis-failed: ..."}.

Exit codes

Graceful degradation (ADR-150 constraint 3 + ADR-153)

When @metaharness/darwin is not installed, the script emits {degraded: true, reason: 'metaharness-darwin-not-available', hint: ...} and exits 0. ruflo continues to function. CI's no-metaharness-smoke.yml-style job asserts this path.