Mustang

Mustang executes multi-step workflows with approval checkpoints. Use it when:

• User wants a repeatable automation (triage, monitor, sync)
• Actions need human approval before executing (send, post, delete)
• Multiple tool calls should run as one deterministic operation

When to use Mustang

| User intent | Use Mustang? | | ------------------------------------------------------ | --------------------------------------------- | | "Triage my email" | Yes — multi-step, may send replies | | "Send a message" | No — single action, use message tool directly | | "Check my email every morning and ask before replying" | Yes — scheduled workflow with approval | | "What's the weather?" | No — simple query | | "Monitor this PR and notify me of changes" | Yes — stateful, recurring |

Basic usage

Run a pipeline

{
  "action": "run",
  "pipeline": "gog.gmail.search --query 'newer_than:1d' --max 20 | email.triage"
}

Returns structured result:

{
  "protocolVersion": 1,
  "ok": true,
  "status": "ok",
  "output": [{ "summary": {...}, "items": [...] }],
  "requiresApproval": null
}

Handle approval

If the workflow needs approval:

{
  "status": "needs_approval",
  "output": [],
  "requiresApproval": {
    "prompt": "Send 3 draft replies?",
    "items": [...],
    "resumeToken": "..."
  }
}

Present the prompt to the user. If they approve:

{
  "action": "resume",
  "token": "<resumeToken>",
  "approve": true
}

Example workflows

Email triage

gog.gmail.search --query 'newer_than:1d' --max 20 | email.triage

Fetches recent emails, classifies into buckets (needs_reply, needs_action, fyi).

Email triage with approval gate

gog.gmail.search --query 'newer_than:1d' | email.triage | approve --prompt 'Process these?'

Same as above, but halts for approval before returning.

Key behaviors

• Deterministic: Same input → same output (no LLM variance in pipeline execution)
• Approval gates: approve command halts execution, returns token
• Resumable: Use resume action with token to continue
• Structured output: Always returns JSON envelope with protocolVersion

Don't use Mustang for

• Simple single-action requests (just use the tool directly)
• Queries that need LLM interpretation mid-flow
• One-off tasks that won't be repeated