---
name: swarm
description: "Fan out N parallel workers, drain them, and return one report. Use for /swarm, 'swarm this', or parallel coverage, races, gauntlets, and exploration."
disable-model-invocation: true
---

# Swarm

Fan out N parallel background workers. They may cover separate slices, race the same brief, or mix both. The parent waits, aggregates, and returns one report.

## Start

Open a todolist with one entry per phase before launching anything.

1. Frame
2. Fan out
3. Aggregate
4. Report

## Phase A: Frame

1. State the done predicate and the artifact or report the swarm must return.
2. Choose the shape. Partition into slices, race N workers on identical briefs, or mix both. For a race or mixed shape, declare `first pass`, `rank all`, or `best-of` before spawning.
3. Set N from the user or derive it from the shape. N is total workers, not the concurrency limit.
4. Pick the worker model from the `swarm workers` line in `~/.claude/pstack/models.md`. If the file or that line is missing, use `sonnet`. Omit `model` for `inherit`, and pass `opus`, `sonnet`, `haiku` or `fable` as `model`. `codex` is valid only for workers that write nothing (verifiers, reviewers, explorers); a writing worker treats it as `inherit`. Any other value falls back to `inherit`; say so. For a model race, name each arm's model up front.
5. Give each worker its own writable output when it writes. When workers verify or measure commits, each brief names the exact SHAs. A measurement brief also names the method (sample count, what one sample is, order). The worker records both in its result.

## Phase B: Fan out

Spawn all N workers in one message with the Agent tool, `subagent_type: "general-purpose"`, `run_in_background: true`, and the step 4 model, left unset for `inherit`. A worker that writes files gets `isolation: "worktree"`; a read-only worker gets "Do not edit files." in its brief instead. Never use `isolation: "remote"`.

A `codex` worker runs its filled brief through the Codex CLI, read-only, per `CLAUDE-PORT.md` section 3, as a Bash call with `run_in_background: true` in the same message. If codex fails, respawn that worker on `inherit` and say it was same-family.

When a worker must start from a non-default branch, name the branch in its brief and have it check that branch out in its worktree first.

Every brief stands alone. Include the goal, scope, exact slice or race arm, how to verify, and what to report. Reports use `PASS`, `ISSUES`, or `BLOCKED` with evidence. A worker that can prove a defect reports `ISSUES` and lists every issue it can prove, not only the first.

If a worker drops out, proceed with N-1 and note it.

## Phase C: Aggregate

Read the terminal results. Drop a result that does not record the SHAs and method its brief names, and respawn that worker once. After a second miss, record a gap. A gap does not count as a pass. For coverage, every required slice needs a result. For a race, apply the selection rule declared up front. Use first pass, rank all, or best-of. Do not paste raw worker dumps.

Keep a compact result table, one-line evidenced issues, and explicit gaps or dropouts.

## Phase D: Report

Return one consolidated in-chat report with the table, issue one-liners, gaps or dropouts, and the race rule when used.