🧑‍🤝‍🧑 pi-subagents — Isolated Subagents for the Pi Coding Agent

@narumitw/pi-subagents is a native Pi coding agent extension that adds a subagent tool for delegating work to specialized agents running in isolated Pi subprocesses.

Use it to split research, planning, implementation, and review work across focused workers while keeping each subprocess context, tools, and prompt boundary separate from the main conversation.

✨ Features

• Registers a subagent tool for single-agent, parallel, fan-in, and chained delegation.
• Runs workers as isolated pi --mode json -p --no-session subprocesses.
• Supports built-in scout, planner, reviewer, and worker agents.
• Loads custom user agents from ~/.pi/agent/agents/*.md.
• Optionally loads project agents from .pi/agents/*.md with confirmation.
• Supports per-task cwd, hard subprocess timeoutMs, abort propagation, and streaming progress.
• Publishes transient runtime status through Pi's generic extension status API while subagents are running.
• Returns complete worker output in tool details and a concise result for the main agent.

📦 Install

pi install npm:@narumitw/pi-subagents

Try without installing permanently:

pi -e npm:@narumitw/pi-subagents

Try this package locally from the repository root:

pi -e ./extensions/pi-subagents

🛠️ Pi tool

pi-subagents registers one tool:

• subagent — delegate work to one or more specialized agents.

Execution modes:

• single — run one { agent, task } job.
• parallel — run multiple { agent, task } jobs independently.
• parallel + aggregator — run parallel jobs, then pass all outputs into one fan-in agent.
• chain — run sequential steps, passing prior output with {previous}.

🧭 Proactive use

The subagent tool now advertises concise prompt guidance so the main Pi agent can choose it without an explicit user request when delegation is a good fit.

Use subagent proactively for:

• Independent read-only research, broad codebase reconnaissance, or high-volume command output that would clutter the main context.
• Parallel multi-domain investigation where each branch can return a concise summary.
• Independent review or verification after implementation, especially with the read-only reviewer agent.

Do not use subagent for:

• Simple answers, quick targeted edits, latency-sensitive one-step work, or tasks that need frequent user back-and-forth.
• Parallel implementation that may edit the same files or shared state; serialize write-heavy work instead.
• Project-local agents unless the user explicitly opts into them with agentScope: "project" or "both"; keep confirmation enabled for untrusted repositories.

Good delegation example:

{
  "tasks": [
    {
      "agent": "scout",
      "task": "Research auth-related source files. Report paths and open questions. Do not edit files."
    },
    {
      "agent": "scout",
      "task": "Research auth-related tests. Report coverage gaps. Do not edit files."
    }
  ],
  "aggregator": {
    "agent": "reviewer",
    "task": "Merge these findings into a concise implementation-risk summary. Use {previous}."
  }
}

Bad delegation example: do not spawn a worker just to rename one symbol in a known file; edit it directly in the main conversation.

🚀 Examples

Run one read-only reconnaissance agent:

{
  "agent": "scout",
  "task": "Find the statusline extension entry points"
}

Run multiple agents in parallel:

{
  "tasks": [
    {
      "agent": "scout",
      "task": "Map package metadata files",
      "timeoutMs": 30000
    },
    {
      "agent": "reviewer",
      "task": "Review TypeScript config consistency"
    }
  ],
  "timeoutMs": 120000
}

Run parallel workers, then aggregate their results:

{
  "tasks": [
    { "agent": "scout", "task": "Find auth-related code" },
    { "agent": "scout", "task": "Find auth-related tests" }
  ],
  "aggregator": {
    "agent": "reviewer",
    "task": "Merge, dedupe, and verify these findings. Use {previous}."
  }
}

Run a chain where each step receives the previous output:

{
  "chain": [
    { "agent": "scout", "task": "Find subagent-related code" },
    {
      "agent": "planner",
      "task": "Using this context, plan the extension: {previous}"
    }
  ]
}

🤖 Built-in agents

Built-in agents are available without setup and can be overridden by user or project agents with the same name.

Agent	Purpose	Tools
scout	Read-only codebase reconnaissance.	read, grep, find, ls, bash
planner	Grounded implementation plans.	read, grep, find, ls
reviewer	Independent review and verification.	read, grep, find, ls, bash
worker	General-purpose implementation.	Pi default tools
general, general-purpose	Aliases for worker.	Pi default tools

Built-in agents inherit the active/default Pi model instead of forcing a provider-specific model alias, which keeps subprocesses usable across different Pi setups.

🧩 Custom agents

Create markdown agent definitions in either location:

• ~/.pi/agent/agents/*.md for user agents.
• .pi/agents/*.md for project-local agents.

Example:

---
name: api-reviewer
description: Review API changes for compatibility and tests
tools: read, grep, find, ls, bash
model: sonnet
---

You are an API review subagent. Do not edit files. Check compatibility,
test coverage, and migration risks. Report PASS/FAIL/PARTIAL with evidence.

By default, subagent loads user agents only. Set agentScope to "project" or "both" to load project-local agents. Interactive sessions ask for confirmation before using project agents unless confirmProjectAgents is disabled.

⏱️ Runtime limits

Each subprocess has a hard timeout to avoid runaway workers.

• Set timeoutMs on the top-level call to apply a default for all jobs.
• Set timeoutMs on a task, chain step, or aggregator to override it locally.
• If omitted, the default is PI_SUBAGENT_TIMEOUT_MS, or 600000 milliseconds (10 minutes) when unset.

On timeout, the extension sends SIGTERM, escalates to SIGKILL after a short grace period, and returns any partial messages or stderr collected so far.

📡 Runtime status

While the subagent tool is running, pi-subagents publishes compact activity status with ctx.ui.setStatus("subagents", "..."). Any statusline extension that reads Pi's generic extension status API can display it; no package-to-package dependency is required.

🔒 Safety notes

Subagents are separate Pi processes and may use the tools allowed by their agent definition. Treat project-local agent prompts like executable project configuration: only enable them in trusted repositories.

🗂️ Package layout

extensions/pi-subagents/
├── src/
│   └── subagents.ts
├── README.md
├── LICENSE
├── tsconfig.json
└── package.json

The package exposes its Pi extension through package.json:

{
  "pi": {
    "extensions": ["./src/subagents.ts"]
  }
}

🔎 Keywords

Pi extension, Pi coding agent, subagents, agent delegation, parallel agents, fan-in aggregation, chained agents, isolated subprocesses, AI coding workflow, TypeScript Pi package.

📄 License

MIT. See LICENSE.