fleet

Fleet — the team in parallel sessions

In-session subagents (the Task tool) share one process and run mostly one at a time through the parent. For real speed on independent work, dispatch the team to separate Claude Code sessions that run in true parallel — each its own process and fresh context. That's the fleet. Used well it's a big speedup; used wrong it burns your quota and creates merge conflicts. The guardrails below are the point.

First decide: should you fan out at all?

Fan out to parallel sessions	Keep it in one session (subagents or sequential)
chunks are independent (separate files/modules, parallel investigations, per-item work)	edits touch the same files, or steps depend on each other
the speedup is worth N× the usage	quota is tight / the job is small
little back-and-forth needed between chunks	frequent coordination is needed (cheaper in one context)

Default to subagent-orchestration (in-session) for most work; reach for the fleet only when the work is genuinely parallel and big enough to matter.

The mechanisms (pick the lightest that fits)

1. Background sessions — the default (interactive). Dispatch each chunk to its own full session:

   claude --bg "review src/auth/ for IDOR"     # or /bg inside a session
   claude agents          # monitor all running sessions
   claude logs <id>       # peek  ·  claude attach <id> — interact with one
   

   The supervisor manages concurrency and auto-isolates each session in its own git worktree, so parallel edits never collide. State lives under ~/.claude/jobs/. This is the recommended way to fan out.
2. Agent teams — when teammates must talk (experimental: export CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS=1). Spawn teammates that share a task list and a mailbox (they message each other via SendMessage). Start with 3–5. Caveats: in-process teammates don't survive /resume, one team per session, no nested teams.
3. Git worktrees — isolate parallel edits. Give each writer its own branch + working directory so concurrent edits never clobber each other (background sessions do this for you automatically; reach for it directly when you dispatch your own parallel editors). See worktree-isolation.

The leader's flow

1. Decompose — break the goal into independent, similarly-sized chunks (use cap-decomposer). Name each chunk's owner files so no two workers touch the same file.
2. Dispatch — one session per chunk, ≤ 3–5 at a time. For edits, prefer background sessions (auto-worktree) or give each its own worktree (worktree-isolation). For analysis/review, have each background session write its findings to a named file.
3. Monitor — claude agents (background) or the team's shared task list. Don't micromanage — workers are autonomous.
4. Integrate — collect each worker's result, resolve any overlap, synthesize the final output, and verify the merged whole (build/tests). A green per-worker result doesn't guarantee a green merge.

Guardrails (do not skip — this is where mistakes happen)

• Cost is linear. N parallel sessions ≈ N× the token/usage burn, and you can hit usage limits N× faster. Cap concurrency (3–5), and only fan out when the speedup earns it.
• Never two workers on one file. Give each chunk disjoint files, or isolate with worktrees. Same-file parallel edits = lost work. The leader owns the merge and the final verify.
• No-resume gotcha. Background workers are one-shot; if one wedges, spawn a replacement rather than trying to resume it.
• Opt-in & safe. The fleet is just Claude Code's own built-in fan-out — background agents, agent teams, and git worktrees — so every session runs with normal permissions (no permission-skipping runner, nothing headless, nothing auto-fans-out; you dispatch each one). The same safe-by-default rules and catastrophe rails hold as the rest of SKULL (no money, no destroying real data, no exfiltration, stay in the project). See SECURITY.md.

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Built on Claude Code's own primitives — background agents, agent teams, and git worktrees. Complements subagent-orchestration (in-session), worktree-isolation (isolation), and model-router + context-engineering (cost). Doc links in docs/ECOSYSTEM.md.