arena git:20261017.8ef3dacA

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---
name: arena
description: "Run several candidates at one task, pick a base, graft in the best of the rest, and return one artifact. Use for /arena, \"경쟁시켜줘\", \"여러 버전 만들어서 비교해줘\", or a design where one attempt would lock in the wrong shape. Split-up work ending in a report is swarm."
---

# Arena

Fan out N parallel attempts at the same task. Read every candidate end to end. Pick the strongest as the base. Graft the best ideas from the others into it. Verify the synthesized result.

A **<name>** principle skill below is `references/principle-<name>.md` in the **principles** skill.

## Phase A: Frame

The N candidates will receive the same prompt, so the prompt is the contract.

1. State the artifact each candidate is producing.
2. Derive the rubric. State what success looks like for *this* task, then turn it into 3-6 concrete gradeable criteria. The rubric is the picker's tool in Phase D. Candidates only see the task.
3. Pick available runners suited to the task and authorized environment. Independent attempts
   may use the same model. Use the host's supported delegation API and configured defaults;
   do not require a particular vendor, model family, plugin, or global installation path.
4. Assign output paths. Each candidate writes to its own location (a git worktree through `isolation: "worktree"` where the artifact lives in the repo, otherwise its own folder in the scratchpad), per the **separate-before-serializing-shared-state** principle skill.

## Phase B: Fan out

Launch every candidate in one message, each with the task, the path to the shared grounding, its own output path, and instructions to produce both the artifact and a short rationale.

Each rationale names the alternatives the candidate considered and what it rejected.

If a candidate fails to produce output, proceed with N-1 and note the dropout in the synthesis record.

## Phase C: Cross-judge

After every Phase B candidate completes, spawn one read-only judge who did not produce the candidates. It sees the rubric and the candidates by path label, scores each criterion, and recommends a base with rationale, while you do your own reading in Phase D.

## Phase D: Pick a base

Read every candidate end to end before picking.

Score each candidate against the rubric criterion by criterion, not on holistic feel. Compare against the cross-judge. Agreement on the base confirms the pick. Disagreement means one of you is biased or the rubric was ambiguous. Read both rationales before deciding.

Pick the base on which candidate a future maintainer can extend most easily without breaking invariants. Prefer the cleaner boundary or smaller API when two feel tied, per the **laziness-protocol** principle skill.

Record the pick and the reason in a short synthesis note alongside the base artifact, including the cross-judge's verdict.

## Phase E: Graft

Walk each losing candidate once more and identify what is worth porting into the base. The signal is usually one or two things per candidate, not most of it.

Fold each graft in by hand, per the **redesign-from-first-principles** principle skill. Don't paste mechanically. The result has to remain coherent under one mental model.

Record what was grafted, from which candidate, and what was rejected and why.

When N candidates converge on the same shape, that is a strong agreement signal. Note the convergence in the record and ship the consensus shape. No graft is needed. When N candidates wildly diverge, Phase A was under-specified. Reframe and re-run rather than averaging the divergence.

## Phase F: Verify

The synthesized artifact has to hold up under the same scrutiny as any other output, per the **prove-it-works** principle skill.

If verification surfaces a problem the arena did not catch, either Phase A was wrong (re-frame and re-run) or one candidate caught it and you missed the graft (go back to Phase E). Don't paper over.

## Outputs

One synthesized artifact. One short synthesis note alongside, naming the base, the grafts (with source candidate), the rejections, the dropouts if any, and the verification result.