pi-subagent
pi-subagent
将 Pi CLI(
@earendil-works/pi-coding-agent)变成一个可编程的编码子代理,任何 MCP 主机(ZCode、Claude Code、Cursor 等)都可以向其委派任务、跟踪会话并终止进程。
pi-subagent 是一个轻量级 MCP 服务器,它将 pi -p --mode json 封装为 7 个结构化工具:委派任务、收集结果、做出调度决策、管理命名会话以及中止运行。进程隔离、完全基于会话、同步/异步双模式。
为什么
Pi 是一个极简的终端编码代理。与其教 Pi 方法论,本项目将 Pi 视为一个可委派的工人:主机代理(ZCode / Claude Code)决定何时委派,发出一个自包含的任务,然后收集结果。一个 Pi 进程 = 一次隔离的子代理运行。
进程隔离 — 每次委派都会生成一个
pi -p子进程。Pi 崩溃只会影响该次运行。完全基于会话 — 每个任务都绑定到一个命名会话(例如
feat-auth);后续调用自动继续。同步 / 异步 — 默认为
async(避免主机工具调用超时);使用pi_status长轮询收集结果。可调度 —
pi_plan是一个纯 5 阶段决策函数(拒绝 / 容量 / 复用 / 修改 / 模式),完全单元测试。通用 MCP — 任何标准 MCP 客户端都可以加载它。
Related MCP server: pi-delegate-mcp
架构
┌─────────────────────────────────────────────────────────────┐
│ MCP Host (ZCode / Claude Code / Pi / Cursor …) │
└───────────────────────────┬─────────────────────────────────┘
│ MCP (JSON-RPC over stdio)
▼
┌─────────────────────────────────────────────────────────────┐
│ pi-subagent-server (Node/TS) │
│ ┌────────────┐ ┌──────────────┐ ┌────────────────────┐ │
│ │ Tool layer │ │ Session │ │ Pi runner │ │
│ │ (7 tools) │─▶│ registry │─▶│ (spawn pi -p) │ │
│ │ + plan() │ │ + persist │ │ parse agent_end │ │
│ └─────┬──────┘ │ + _snapshot │ │ + tool_execution │ │
│ │ └──────────────┘ └─────────┬──────────┘ │
│ │ ┌────────▼─────────┐ │
│ └───────────────────────────│ Run registry │ │
│ (kill) │ + process-table │ │
│ └──────────────────┘ │
└─────────────────────────────────────────────────────────────┘
│ child_process.spawn({ cwd })
▼
┌─────────────────────┐
│ pi CLI (0.77+) │
└─────────────────────┘三层边界清晰:工具层(MCP 模式 + plan() 纯函数)/ 会话注册表(状态 + 持久化 + 脱敏)/ 运行器(生成 pi、解析 NDJSON、进程表)。
工具
工具 | 用途 |
| 决定:是否应委派、同步/异步、多少个会话 |
| 派发任务(默认异步;新会话等待握手) |
| 收集运行结果(长轮询) |
| 列出会话(省略 |
| 检查单个会话 |
| 分支一个会话以尝试另一条路径 |
| 中止运行 |
| 创建多阶段任务(主机先写入 |
| 派发对计划的领域审查(通过 |
| 运行一个阶段:同步(等待结果)或异步(返回 runId) |
| 收集异步阶段运行;自动判断并重新派发(最多 3 次),否则手动 |
| 列出任务(按 taskId / 状态过滤) |
审查循环:在
pi_task_plan之后,使用pi_status(runId)收集结果。当运行完成时,服务器检测到这是审查运行,解析_plan-reviewed.md,并将planVerdict/planReviewedPath存储在任务上。阶段提示自动包含已审查的计划和已通过依赖阶段的输出文件。
异步阶段:向
pi_task_stage_run传递mode: "async"以避免阻塞工具调用整个运行(当 MCP 主机强制短工具超时时推荐)。使用pi_task_stage_collect(taskId, stageId)收集。失败的尝试会在新的会话名称下重新派发,以避免历史污染;3 次失败后,阶段进入manual状态,并显示决策面板(通过promptHintOverride支持retry_with_new_hint)。
重启恢复:使用相同的
taskId重新运行pi_task_create会合并而不是冲突。输出文件已存在且通过验证的阶段会自动标记为passed,因此中断的任务无需手动编辑tasks.json即可恢复。
会话模型
每个会话都有一个人类可读的名称 + Pi 的 UUID +
cwd+goal。第一次
pi_delegate创建会话(需要goal);后续调用自动继续。注册表持久化到
~/.pi-subagent/registry.json(原子写入;重启时,中断的running记录会被纠正为error)。并发上限:4 个正在运行的运行;单个会话永远不会并发运行。
任务持久化到
~/.pi-subagent/tasks.json(原子写入;重启时,正在运行的阶段会被纠正为failed(interrupted_by_restart))。
安装
git clone <this-repo> && cd pi-subagent
npm install先决条件:pi CLI 已安装(npm i -g @earendil-works/pi-coding-agent)并在 PATH 中。
配置 MCP 主机
添加到您的 MCP 客户端配置:
{
"mcpServers": {
"pi-subagent": {
"command": "npx",
"args": ["tsx", "/abs/path/to/pi-subagent/src/server.ts"]
}
}
}可选环境变量:
PI_SUBAGENT_REGISTRY— 注册表路径(默认~/.pi-subagent/registry.json)PI_BIN— 覆盖 pi 可执行文件(用于测试)
测试
npm test # full suite (140 tests)
npm run test:fast # dot reporter测试使用一个假的 pi(test/fixtures/fake-pi.sh),涵盖:异步/同步、超时、终止、会话创建失败、多等待者、进度上限、调度规则(表驱动 + 100 次迭代属性测试)、注册表持久化、脱敏等。
项目布局
src/
├── types.ts # all shared types + error codes
├── errors.ts # ToolError helpers
├── runner/ # parse.ts, argv.ts, spawn.ts, process-table.ts
├── registry/ # session.ts, run.ts, persist.ts, redact.ts
├── scheduler/ # keywords.ts, plan.ts (5-stage pure function)
├── tools/ # delegate, status, plan-tool, session, kill
└── server.ts # MCP entry (stdio)
skills/pi-subagent/ # SKILL.md + delegation-patterns (strategy layer)
test/ # fixtures/ + *.test.ts
docs/ # design.md (spec) + implementation-plan.md设计与流程
本项目在实现之前经历了协作设计 + 4 轮外部审查。规范和计划已提交在 docs/ 下:
docs/design.md— 完整的设计规范(架构、工具契约、错误处理、调度器规则、测试策略)。每个契约都可追溯到审查注释(R1–R4)。docs/implementation-plan.md— 19 个 TDD 任务(编写失败测试 → 实现 → 通过 → 提交)。
关键设计决策,均基于对 pi -p 输出的实际探测和外部审查:
cwd≠ 会话存储 —spawn({ cwd })控制工作目录;Pi 的会话文件使用其默认位置(不污染项目)。异步默认 + 握手 — 新会话在返回之前等待 Pi 的
session事件(带有sessionStartTimeoutMs),因此主机始终获得真实的piSessionId。多阶段调度器 —
plan()是拒绝 → 容量 → 复用 → 修改 → 模式,其中修饰符堆叠而不是首次匹配(来自审查第 1 轮的教训)。进度脱敏 — 工具结果在存储之前会被截断并清除令牌/密钥。
状态
可工作的实现,140 个通过的测试。尚未发布到 npm — 通过 tsx 从源码运行。
许可证
MIT
Available Tools
7 toolspi_delegateC
委派任务给 Pi 子代理(默认 async)
| Name | Required | Description | Default |
|---|---|---|---|
| cwd | No | ||
| goal | No | ||
| mode | No | ||
| prompt | Yes | ||
| session | Yes | ||
| constraints | No | ||
| runTimeoutMs | No | ||
| allowUnknownTools | No |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description must disclose behavioral traits but only mentions 'default async'. It does not explain side effects, how results are returned, or whether the tool is idempotent. Critical details are missing.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single concise sentence, but it is overly terse for a tool with 8 parameters. While front-loaded, it lacks structure and does not fully utilize the space to convey necessary information.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the complexity (8 parameters, nested objects, no output schema, no annotations), the description is severely incomplete. It fails to cover usage patterns, return values, or async/sync behavior beyond the default.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 0%, and the description does not explain any of the 8 parameters, not even the required 'prompt' and 'session'. The enum for 'mode' is mentioned only implicitly as 'default async' but no details.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states that the tool delegates tasks to a Pi sub-agent with a default async mode. However, it does not differentiate from sibling tools like pi_plan or pi_session_fork, which could have overlapping functionality.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
No guidance is provided on when to use this tool versus alternatives, nor are there any preconditions or exclusions mentioned. The description is too brief to inform decision-making.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
pi_killC
中止 run
| Name | Required | Description | Default |
|---|---|---|---|
| runId | Yes |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations exist, so the description must fully disclose behavior, but it only states '中止 run' without detailing side effects, reversibility, or required permissions.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Extremely short but at the expense of clarity; it fails to provide necessary information, making it underspecified rather than appropriately concise.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
A kill operation with one parameter is simple, but the description omits return values, error cases, and prerequisites, rendering it incomplete for reliable agent invocation.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
The only parameter 'runId' has no description in the schema or in the text, leaving its purpose and format entirely unspecified.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description '中止 run' conveys the action (abort) and resource (run), but is in Chinese and does not differentiate from siblings like pi_delegate or pi_plan.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
No guidance provided on when to use this tool versus alternatives, nor any context about prerequisites or typical scenarios.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
pi_planC
调度决策:该不该委派、sync/async、开几个 session
| Name | Required | Description | Default |
|---|---|---|---|
| cwd | Yes | ||
| task | Yes | ||
| fanout | No | ||
| estComplexity | No | ||
| preferredMode | No |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations provided; the description does not disclose side effects, authorization needs, or whether the tool is read-only or modifies state. The term '决策' implies decision-making but no details on consequences.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is very concise (one line). It is front-loaded with the core idea, but at the cost of missing important details. It could be slightly expanded without being verbose.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given 5 parameters, no output schema, and no annotations, the description is insufficient. It does not explain return values, parameter usage, or behavioral traits, making it hard for an agent to use correctly.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
0% schema description coverage; the description does not explain parameter semantics beyond their names (e.g., fanout, estComplexity). Field names give some clues but are insufficient for proper invocation.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description '调度决策:该不该委派、sync/async、开几个 session' indicates it is for scheduling decisions, but it is vague. It mentions delegation and session management, aligning with sibling tools like pi_delegate and pi_session_fork, but does not clearly state the tool's specific action or output.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
No guidance on when to use this tool versus alternatives. The description does not mention prerequisites, when to delegate or not, or how this relates to other tools like pi_delegate or pi_session_fork.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
pi_session_forkD
派生 session
| Name | Required | Description | Default |
|---|---|---|---|
| to | Yes | ||
| from | Yes |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations provided; description is too minimal to disclose behavioral traits like destructiveness, permissions, or lifecycle impact.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Extremely brief but at the expense of completeness. Not a model of efficiency; it omits essential information.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a tool with two required parameters and no output schema or annotations, the description provides zero contextual completeness.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 0%; description fails to explain what 'from' and 'to' represent, leaving all parameters underspecified.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
Description is a single Japanese phrase '派生 session' meaning 'fork session'. It suggests duplication but lacks a clear verb-resource structure or differentiation from siblings.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
No guidance on when to fork vs using siblings like pi_session_list or pi_session_snapshot. No context provided.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
pi_session_listA
列 session(不传 cwd 取全量,供 pi_plan 用)
| Name | Required | Description | Default |
|---|---|---|---|
| cwd | No |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries full transparency burden. It implies a read-only operation ('list') and explains cwd filtering behavior, but does not disclose potential side effects, auth requirements, or other safety guarantees. Adequate but minimal.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single sentence, front-loaded with the action, and contains no superfluous information. Every word adds value.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool's simplicity (one optional param, no output schema), the description covers purpose, parameter behavior, and intended usage context. It does not explain return format, but for a list operation this is acceptable. Slightly more detail would improve completeness.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 0%, so the description must compensate. It explains that omitting cwd returns all sessions, adding meaningful semantics beyond the bare schema. This provides sufficient guidance for a single optional parameter.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the verb 'list' and resource 'session', with additional detail on behavior when cwd is omitted. It also specifies use for pi_plan, distinguishing it from sibling tools like pi_session_fork or pi_session_snapshot.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides context on when to use the tool (for pi_plan) and the effect of omitting cwd. It does not explicitly state when not to use it or mention alternatives, but the guidance is clear enough for an AI agent.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
pi_session_snapshotC
取 session 详情
| Name | Required | Description | Default |
|---|---|---|---|
| session | Yes |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations provided. The description implies a read operation but does not explicitly state it is non-destructive or disclose any behavioral traits.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Very concise but under-specified. A single phrase with no additional structure or front-loading of key information.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the simplicity (1 param, no nested objects, no output schema), the description is incomplete. No information on return value, behavior, or context.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 0%. The parameter 'session' lacks any description in both schema and tool description, leaving its meaning ambiguous.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description '取 session 详情' clearly indicates fetching session details. It distinguishes from siblings like pi_session_list (listing) and pi_session_fork (forking) but does not specify the snapshot aspect.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
No guidance on when to use this tool versus siblings. No context on prerequisites or alternatives.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
pi_statusC
取 run 结果(long-poll)
| Name | Required | Description | Default |
|---|---|---|---|
| runId | Yes | ||
| waitTimeoutMs | No |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries full burden. It mentions 'long-poll' implying blocking behavior, but does not disclose idempotency, destructiveness, authentication needs, or error handling. The transparency is minimal.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is extremely short (one phrase), which is concise but lacks structure. It front-loads the core purpose but does not provide enough detail to be fully helpful.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool has two parameters and no output schema, the description is insufficient. It omits details on return format, long-poll behavior nuances, timeout semantics, and relationship to sibling tools.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 0% and the description does not explain any parameters. 'runId' and 'waitTimeoutMs' remain undocumented in meaning. The description adds no value beyond the schema's structural definition.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the verb '取' (get) and resource 'run result' with 'long-poll' qualifier. However, it does not distinguish this tool from siblings like pi_kill or pi_plan, which are distinct actions but no explicit differentiation is provided.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
There is no guidance on when to use this tool versus alternatives. It does not mention prerequisites, context, or conditions for use. The description is purely functional.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Tool Schema Changelog
Recent tool additions, removals, and schema changes observed during successful MCP inspections.
7 tool updates
v0.1.0- First observed
pi_delegate - First observed
pi_kill - First observed
pi_plan - First observed
pi_session_fork - First observed
pi_session_list - First observed
pi_session_snapshot - First observed
pi_status
TDQS
Scored across 7 tools
Each tool targets a distinct operation: delegation, kill, planning, session management, and status. No overlap in purpose.
All tools share the 'pi_' prefix, but the structure varies: some are verbs (pi_delegate, pi_kill), others are noun_verb (pi_session_fork). Overall readable and consistent prefix helps.
7 tools is appropriate for a subagent manager covering delegation, planning, session lifecycle, and status retrieval.
Core operations are covered, though missing explicit session creation or update tools. Forking may serve creation, and kill provides termination.
Maintenance
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