subagent — one-shot / batch / background provider subagent

Wrong lane? A long-lived collaborator you message back and forth → /cc-fleet:team; a multi-phase pipeline with dependencies or resume → /cc-fleet:workflow; arbitration in cc-fleet-shared/routing.md.

When this skill cites cc-fleet-shared/<file>.md, OPEN it with the Read tool at ../cc-fleet-shared/<file>.md relative to this SKILL.md — the cited content is load-bearing, not optional background.

Execution environment — check before running anything. Confirm your shell tool executes on the host where cc-fleet is installed. In sandboxed or remote agent sessions, a tool named Bash may run on an isolated machine with a different filesystem, PATH, processes, and tmux server — command not found, a healthy-looking doctor whose leaves can't reach your files, or a wrong working directory should prompt you to verify whether you are in a sandbox shell, not conclude that cc-fleet is broken. If so, route commands through a host-executing bridge tool (for example, desktop-commander) and pass host paths for any files you reference; do not retry the same Bash call expecting different results. If no host-executing tool is available, stop and explain that cc-fleet must run on its installation host.

cc-fleet subagent runs a provider model headless and returns the result directly on Bash stdout — no tmux pane, no team, no SendMessage. The analog of the native Agent/Task tool, but the model can be a provider id. It reuses the same provider selection as the teammate lane and needs only a claude binary on the host. It's the lightweight synchronous branch.

When to use it

• One-shot research / analysis / judgement — you want an answer, not a long-lived colleague.
• Batch fan-out — N independent tasks in parallel. subagent is lock-free, so N calls don't serialize behind each other — true parallelism.
• Cost-bounded probes — --timeout caps wall-clock; the return value carries usage / total_cost_usd; it stops when done (nothing to forget to tear down).

The provider ask ladder (ask at most once per task)

1. The user named a provider or model → use it.
2. Else run cc-fleet default --json: if it returns a provider (source "configured" or "auto"), use it and STATE it in your kickoff line (e.g. "using glm (default)").
3. Else (several providers, none default) ask the user ONCE which to use — list the enabled providers from cc-fleet list --json (name + default_model + the one-line note in cc-fleet-shared/providers.md). After they pick, run cc-fleet default <chosen> so you never ask again. (cc-fleet default <p> is user-layer; only run it to FILL a blank default, never with --force.)
4. A mid-task provider failure (insufficient balance / rate limit / auth) → STOP, tell the user what happened, propose the next provider, and WAIT for their confirmation. Never switch providers silently.

STOP freezes the affected provider operation and any unapproved provider switch, not independent authorized work. The error table's single rate-limit retry remains allowed; do not retry uncertain writes before establishing their prior result. Main-session handling is allowed only where the workflow already permits it and the user has not required that provider. Changing a provider or the saved default still requires the corresponding explicit authorization.

Model tier within a provider: fan-out / leaf work → omit --model (or --model fast); judge / synthesis / sustained work → --model strong. The provider's roster decides the actual model — see cc-fleet-shared/providers.md.

The reserved native leaf — `claude`. cc-fleet subagent claude … runs the official claude CLI on the user's OWN Claude Code login (their subscription OAuth or whatever they're logged in as) — no providers.toml row, no profile, no key material. A NAMED deliberate choice, never the auto-default (cc-fleet default claude errors; it never auto-resolves). --model takes a literal id (fable / opus / sonnet / a full id) — the slot keywords default/strong/fast are rejected (no roster); omitted = claude's login default, which is typically the most expensive tier, so naming a model is usually wise. Profiles apply unchanged. The leaf spends the lead session's own subscription window — use it for one or two synthesis / judgement nodes, never a wide fan-out.

cc-fleet subagent claude --model opus --prompt "<synthesis over the gathered notes>" --json

Calling it (run via Bash, always with --json)

cc-fleet subagent --prompt "<task>" --json                 # no provider arg → default provider
cc-fleet subagent deepseek --model strong \
  --prompt "Analyze the worst-case complexity of quicksort in src/sort.go; give a triggering input" --json

The provider arg is optional — with no provider, cc-fleet uses the default. NO_DEFAULT_PROVIDER / DEFAULT_PROVIDER_DISABLED / DEFAULT_PROVIDER_UNKNOWN in the failure envelope mean there is no usable default — apply the provider ask ladder above.

Session grouping — no flag needed. cc-fleet subagent auto-detects the parent Claude session (fail-closed: an unvalidatable registry shows (no session), never a guess) — the same live session id the Agents Board groups your teammates under. The envelope's lead_session_id is the id subagent-gc --session takes. --lead-session-id <id> overrides detection, but never copy it from ~/.claude/teams/<team>/config.json: the implicit team keeps its startup session id after /clear, /resume, --resume or --continue.

Useful flags (full list: cc-fleet subagent --help):

• Name it → --label "<short-alias>" (e.g. --label sort-complexity). The Agents Board shows the label instead of the opaque job id — pass one on every launch, like a teammate name. Display-only metadata; capped at 256 bytes.
• Large / sensitive prompt → --prompt-file <path> (read from file, piped via stdin, kept out of argv / ps). Use it once a single prompt approaches ~128 KiB (MAX_ARG_STRLEN, the per-argument cap — not the ~2 MB total ARG_MAX). --prompt-file - reads stdin.
• Long task → --timeout 600s (default 300s). For tasks that may exceed the timeout, run the sync call in a backgrounded Bash, or use --background (both below). Note: a provider that's down on auth (401) or quota (429) makes claude retry ~180s before surfacing KEY_INVALID / INSUFFICIENT_BALANCE, so keep --timeout ≥ ~200s (the 300s default is fine) — a shorter timeout reports those as SUBAGENT_TIMEOUT instead. --probe does not catch a bad key (the models endpoint may not 401 it).
• Cost / runaway gates → --max-budget-usd 0.5 (cap spend) and --max-turns (cap the agentic tool loop). On fan-out, strongly consider a budget cap on every call. Size `--max-turns` generously up front — a read-heavy / multi-file / git-inspecting task spends ~1 turn per file read or command, so give it 30–50 (or omit it); a small cap (8/10) starves it and the leaf fails SUBAGENT_MAX_TURNS mid-task.
• Prompt profile — slim is the DEFAULT; read-only research → --profile slim-ro; --profile full ONLY to compare against a full session or diagnose a suspected slim regression. --tools REPLACES the whole tool set, never appends. Write prescriptive prompts ("Run cmd", "Use the Read tool on X"), not "look at" / "check" — weak provider models skip tools on weak imperatives under any profile. Tool whitelists / --skills / --mcp defaults / downgrade behavior: cc-fleet-shared/providers.md.
• Probe is off by default (--probe to opt in): the inner claude -p call is itself the authoritative reachability + auth test. On a big fan-out, run one shared cc-fleet doctor / probe up front rather than paying up to 10s × N.
• --prompt and --prompt-file are mutually exclusive — pass exactly one (else error_code=SUBAGENT_BAD_ARGS, no claude launched).

Success envelope

{"ok":true,"result":"<answer text>","provider":"deepseek","model":"deepseek-reasoner",
 "duration_ms":12044,"usage":{"input_tokens":812,"output_tokens":1530},
 "total_cost_usd":0.0031,"session_id":"…"}

→ Take .result as this subagent's output and hand it back / continue orchestrating. model is the model the provider actually billed (routing evidence). Keep .session_id if you intend a multi-turn follow-up (below).

Failure envelope — dispatch on error_code (do not parse prose)

error_msg is a canonical string only; never matched on. Dispatch on error_code:

Batch fan-out (parallel, each returns synchronously)

# These Bash calls are independent and can fire in parallel; subagent is
# lock-free, so they don't queue behind each other.
cc-fleet subagent glm      --prompt "Summarize docs/a.md" --json
cc-fleet subagent glm      --prompt "Summarize docs/b.md" --json
cc-fleet subagent deepseek --prompt "Summarize docs/c.md" --json
# Each returns its own {ok, result, total_cost_usd}; aggregate them. No
# team or teammate needed.

A flat fan-out only — phases, dependencies, or dynamic orchestration over the results is /cc-fleet:workflow.

Long tasks: a backgrounded Bash is the push notification

A finished subagent CAN wake you: a backgrounded Bash command's exit is delivered to the session as a task notification. Never spawn an agent (or loop yourself) to poll. Two shapes:

1. Sync call in a backgrounded Bash (first choice). Run the ordinary cc-fleet subagent … --json with the Bash tool's run_in_background=true, end your turn, and the harness wakes you when it exits — the envelope is the task output. Zero extra mechanism; the process is tied to your session.
2. `--background` + a waited status — when the job must survive your session, or you want it grouped on the Agents Board:

cc-fleet subagent --prompt "<long task>" --background --json
# → {"ok":true,"job_id":"<uuid>","status":"running","output_file":"…","pid":…}
# arm the notifier (backgrounded Bash — its exit wakes you):
cc-fleet subagent-status <job_id> --wait --timeout 5m --json

Wake-up dispatch on the exit code: 0 done (envelope has .result) · 1 failed OR stopped — check .status first: stopped is an operator stop, never auto-retry; failed, or no .status (an invalid or unknown job id) → dispatch on .error_code · 3 held (a workflow-leaf id an operator parked — surface it, never wait it out) · 124 still pending at --timeout (a heartbeat: re-arm; escalate only if the job is far past its own --timeout) · 130 interrupted. Always pass --timeout, and re-arm any still-pending wait after a session restart.

cc-fleet subagent-gc --json prunes finished job files.

Multi-turn: --resume

Continue a prior subagent session (stateful, but not long-lived between turns — each turn is a fresh claude -p --resume):

cc-fleet subagent --resume <session_id> --prompt "<follow-up>" --json

<session_id> is the .session_id from the previous turn's envelope. A default-profile (slim) resume is silent; an explicitly passed --profile over --resume warns on stderr — it swaps the system prompt mid-session. Keep the profile constant across a session's turns.

Cleanup vs. resume — they're independent

A sync subagent has nothing to tear down; "cleanup" only concerns --background job records on the Agents Board. The rules:

• The one rule that matters: capture `.session_id` BEFORE pruning if a follow-up is likely. gc deletes cc-fleet's job record (which holds the envelope with the id) but never Claude's transcript — so --resume works after gc iff you kept the id, and keeping the record without the id buys you nothing.
• Prune finished, scoped to your session: cc-fleet subagent-gc --session <lead_session_id> --json (immediate, skips pinned) — prefer it over a blanket subagent-gc --older-than 0s so you never wipe another session's records. Default gc only removes finished jobs older than 24h; running jobs are always kept; pinned records are user-owned — never force-remove them.
• gc also deletes workflow runs. Any subagent-gc deletes the runs it reaches (--session: that session's finished runs, at once; the default: runs idle past the cutoff) with their journals and saved scripts, so workflow run --resume / restart can no longer replay them — resume or abandon a stopped or failed run before pruning. A stopped or killed run's leftover isolation worktree is first saved to a cc-fleet/wf-salvage-* branch (or kept with a .cc-fleet-keep marker if that fails); gc prints no notice, so check git branch --list 'cc-fleet/wf-*', and git worktree list for a kept directory.

Anti-patterns

• Using subagent for work that needs multiple turns / collaboration → /cc-fleet:team.
• Chaining subagents into a dependent pipeline by hand → /cc-fleet:workflow.
• SendMessage / polling cc-fleet ps --check for a subagent → unnecessary; the result is on stdout.
• Stuffing a giant prompt into --prompt (hits MAX_ARG_STRLEN ~128 KiB) → use --prompt-file.
• Running a possibly-stuck provider with no bound → the default --timeout 300s caps it, but tune per task on fan-out, and run genuinely long work via a backgrounded Bash or --background (Long tasks above).
• Polling subagent-status in a loop (or delegating an agent to watch a job) → arm subagent-status --wait in a backgrounded Bash once; its exit is the notification.
• Looping on a failure without dispatching .error_code → every --json failure carries a code; switch on it (table above; teammate-side codes in cc-fleet-shared/troubleshooting.md).
• Switching providers silently after a balance / rate-limit / auth failure → stop, tell the user, wait for their pick (provider ask ladder, step 4).
• Fanning out N claude native leaves → drains your own subscription window; use a metered provider for breadth, claude only for one or two synthesis nodes.