arena

name	arena
description	Produce one artifact by fanning out N blind candidates, picking the strongest as the base, grafting the best of the losers into it, and verifying the synthesis. Use when a single attempt at a non-trivial artifact — a design, a tricky function, a doc — would lock in the wrong shape.
argument-hint	[the artifact to produce]

Arena

Artifact: $ARGUMENTS

One attempt commits to one shape. When the shape is the risk, produce several shapes in parallel and synthesize the best of them.

1. Frame the contract

Write the task once: what the artifact is, the constraints it lives under, and the rubric it is judged against — the concrete properties that make one version better than another. Every candidate receives this same text.

2. Fan out

Dispatch N fresh-context sub-agents (default 3, cap 5) in a single message so they run concurrently. These are ad-hoc dispatches: name the agent type and pass an explicit model (default opus), never the inherited session one. Each gets the contract, its own output path under ./tmp/arena/<slug>/candidate-1..N/, and no knowledge of the others. Candidates write inside their own path and leave the working tree untouched — concurrent writers otherwise overwrite each other. Each dispatch carries the leaf-agent line — you are a sub-agent; never spawn agents or invoke agent CLIs — so the fan-out stays one level deep.

Ask every candidate for the artifact plus a short rationale: what it chose, and what it considered and dropped.

3. Pick the base

Read every candidate end to end before judging any of them. Score each against the rubric and pick the base: the one a future maintainer extends most easily without breaking its invariants. Name the winner and the rubric line that decided it.

4. Graft

Move the strongest one or two ideas from each losing candidate into the base, adapted to the base's shape. The losers' rationales are where grafts come from — they name ideas the winner never considered.

5. Land and verify

Write the synthesis to the artifact's real destination — the file it ships in, out of ./tmp/, which is scratch. Uncommitted work already at that destination gets committed or confirmed first, and a write reached for on your own initiative waits for the user's ask. Then run the repo's checks against it — the build/typecheck/lint workflow its own AGENTS.md, package scripts, or CI config names — or the task's own acceptance test. Every graft is new code, and this combination is one nobody produced or checked.

Report

• the winner and why it won;
• each graft and the loser it came from;
• verification evidence: the command run and its result;
• where the artifact now lives.