pi-subagents Package

Source: https://pi.dev/packages/pi-subagents (docs: https://github.com/nicobailon/pi-subagents/tree/main/docs)

Delegate work to focused child Pi sessions: code review, scouting, implementation, parallel audits, saved workflows, background jobs. Installing the extension does not start anything automatically — it gives Pi a subagent delegation tool.

pi install npm:pi-subagents

Users normally ask in plain language ("Use reviewer to review this diff", "Run parallel reviewers for correctness, tests, and complexity"). Pi decides whether to call the tool, which agent to use, and how to compose the work.

Built-in Agents

Builtins load at the lowest priority and inherit the current Pi default model unless subagents.defaultModel or an override says otherwise. Packaged worker, oracle, and advisor default to context: "fork"; others default to fresh. Builtins opt into project-instruction inheritance so they follow repo rules.

Recommended implementation loop: clarify → scout → worker → fresh reviewers → worker.

Execution: workflowScript

All model-facing execution goes through workflowScript — an ordinary JavaScript statement body with an explicit return. The legacy /chain, /parallel, /run-chain, and /chain-prompts commands are no longer registered, and .chain.md/.chain.json files exist only as durable legacy chains.

// One child
subagent({ workflowScript: `return runs.run("main", { agent: "scout", task: "Analyze the auth flow" })` })

// Sequential
subagent({ workflowScript: `
  const scan = await runs.run("scan", { agent: "scout", task: "Analyze auth" });
  return (await runs.run("implement", { agent: "worker", task: "Implement from: " + scan.output })).output;
` })

// Parallel
subagent({ workflowScript: `
  const reviews = await runs.all([
    { key: "correctness", agent: "reviewer", task: "Review correctness" },
    { key: "tests", agent: "reviewer", task: "Review tests" }
  ]);
  return reviews.map(r => r.output);
` })

Globals inside the script: runs.run(key, opts), runs.all([items]), runs.ref, state.get/set (durable mission JSON state), and prompts.render(ref, vars?). For long task text containing Markdown fences or shell blocks, build the string from quoted lines joined with \n rather than a raw template literal.

Workflows default to background execution; pass async: false for a watched foreground run with a live in-chat card (chatProgress forces auto/off/live-card). Foreground workflows default to a 30-minute timeout; async workflows have no default top-level timeout.

prompts.render needs an explicit scope: package:<name>, user:<name>, or project:<name>, each naming a top-level <name>.md. Frontmatter is stripped, scalar {{name}} placeholders are substituted, and unknown placeholders stay unchanged. Rendering returns text only — pass it explicitly as task.

Key Tool Parameters

agent, action, topic, chainName, config, context (fresh/fork — an explicit value overrides every workflow child; otherwise each child uses its own defaultContext), missionId, mission (object or false), handoffPath, view (fleet/transcript), lines (default 80, max 500), agentScope, async, chatProgress, timeoutMs/maxRuntimeMs, toolTimeoutMs, turnBudget, toolBudget, usageBudget, cwd, maxOutput (200 KB / 5000 lines), artifacts, includeProgress, share, sessionDir, acceptance, gate, plus per-item output, outputMode, skill, model, worktree, resume.

Budgets: turnBudget is { maxTurns, graceTurns } (warn at maxTurns, terminate at the next assistant boundary after the grace window); toolBudget is { soft?, hard, block? } (block defaults to read/grep/find/ls; "*" blocks everything, final assistant text never blocked); usageBudget is root-only { tokens?: { soft?, hard }, costUsd?: { soft?, hard } } where soft limits are status-only and hard limits prevent later child launches without stopping running ones. Do not set turn, hard tool, or tight usage budgets on mutation-capable children (implementation workers, fix workers, reviewers with edit authority) — none of those measure whether a delivery slice is buildable, and a default tool budget blocks read/search tools rather than mutations. Bound writers with a narrow task and an outer timeoutMs instead, and request a checkpoint via steer before the deadline.

context: "fork" fails fast when the parent session is not persisted, the leaf is missing, or the branched session cannot be created — it never silently downgrades to fresh. Forking strips signed Anthropic thinking/redacted_thinking blocks from the child session and forces thinking off when the child's effective primary or fallback model resolves to the Anthropic provider or anthropic-messages API (unresolved models are treated conservatively). Use fresh when an Anthropic child needs thinking.

outputMode: "file-only" returns a compact pointer (Output saved to: /abs/report.md (48.2 KB, 2847 lines)…) instead of inline text; failed runs and save errors still return inline output for debugging. A read-only child does not need filesystem access for output — it returns the artifact in its final response and the runtime persists it.

Retained Children

Completed workflow children from the current parent session stay addressable. { action: "children.list" } lists up to the last 10 with run ids; a later workflow continues one by passing resume instead of agent:

subagent({ workflowScript: `
  let writer = await runs.run("implement", { agent: "worker", task: "Implement the accepted contract" });
  for (const pass of [1, 2]) {
    const task = await prompts.render("project:writer-followup", { pass, previous: writer.output });
    writer = await runs.run("followup-" + pass, { resume: writer.runId, task });
  }
  return writer;
` })

Each resume can return a new retained run id, so loops must continue from the latest runId. resume and agent are mutually exclusive, the revived child keeps its stored agent/model/tool contract, and gate is rejected on resume items. Top-level { action: "resume" } stays detached and returns a background receipt — use it for a simple challenge outside a script; use runs.run({ resume }) only when the script must await the revived output. steer with mode: "follow_up" only queues text for the next resume; it does not revive a completed child.

Commands

/run <agent> [task] [--bg] [--fork]     # one child
/subagents-fleet                        # live fleet inspector
/subagents-stop [run-id]                # stop a top-level async run
/subagents-detach [run-id]              # leave a foreground run running
/subagents-doctor                       # read-only setup diagnostics
/subagents-guide [topic]                # packaged docs for the installed version
/subagents-refine <agent>               # project-local refinement overlay
/subagents-models [agent]               # live runtime model mapping
/subagents-watchdog [status|on|off|recommend-model|model ...|session model ...|check]
/subagents-refresh-provider-models <provider> [--force]
/subagents-generate-profiles <provider> | /subagents-load-profile <name> | /subagents-check-profile <name>
/prompt-workflow <template> [args]      # run a subagent prompt template

Per-run overrides use bracket syntax on the agent name: /run reviewer[model=anthropic/claude-sonnet-4:high] "Review this diff".

Packaged prompt shortcuts: /parallel-review, /review-loop, /parallel-research, /gather-context-and-clarify, /parallel-cleanup (add autofix to /parallel-review or /parallel-cleanup to apply only the synthesized fixes worth doing now).

/subagents-guide and { action: "guide", topic } read the packaged docs for the installed version. Topics: overview, workflows, agents, missions, observability, tool-reference, configuration, models, watchdog, extension-api.

Management, Status, and Control Actions

{ action: "list" | "get" | "create" | "update" | "delete" | "eject" | "enable" | "disable" | "reset" }
{ action: "children.list" }
{ action: "refine" | "refine.show" | "refine.rollback", agent: "reviewer" }
{ action: "status" }                                            // all active runs
{ action: "status", view: "fleet" }
{ action: "status", id: "<run-id>", view: "transcript", index: 0, lines: 80 }
{ action: "interrupt" | "stop", id: "<run-id>" }
{ action: "resume", id: "<run-id>", index: 1, message: "follow-up" }
{ action: "steer", id: "<run-id>", mode: "steer" | "follow_up" | "auto", message: "guidance" }
{ action: "grant-spawn-budget", additional: 10 }
{ action: "doctor" }
{ action: "watchdog.recommend-model" } | { action: "watchdog.configure", model: "recommended", scope: "session" | "user" | "project" }
{ action: "mission.create" | "mission.list" | "mission.show" | "mission.update"
  | "mission.resolve-decision" | "mission.attach-run" | "mission.close" }
{ action: "schedule.create" | "schedule.list" | "schedule.show" | "schedule.history"
  | "schedule.pause" | "schedule.resume" | "schedule.run" | "schedule.run-due" | "schedule.delete" }
{ action: "inspector.open" | "inspector.status" | "inspector.close", id, index, focus }
{ action: "project.open" | "project.status" | "project.close", cwd, message }

create uses config.scope (not agentScope); config.package registers the runtime name as {package}.{name}; config.aliases accepts a comma-separated string, array, or false. Clear optional string fields with false or "". eject copies a bundled builtin or package agent verbatim into the user/project agent dir as an editable shadow; reset deletes the scope's custom file and/or override entry, restoring the bundled default (it refuses when no bundled default exists — use delete for purely custom agents). These accept agentScope: "user" | "project" and operate on one scope at a time; a project-scope disable survives a user-scope enable.

status resolves exact foreground ids, top-level async ids, and nested run ids before prefix matching. stop is stronger than interrupt: it is not a resumable pause, rejects foreground and nested targets, and stopped runs must be restarted as new runs. resume revives a paused, completed, or failed child from its stored session file by starting a new child process, taking an exclusive cross-process lease on the canonical session file. steer waits up to three seconds for correlated acceptance and returns a request id with delivered/scheduled/pending/partial/recovered/failed plus deliveryStatus: "delivered" | "queued"; the FIFO holds 20 messages and the persisted steering ledger retains 20 requests. append-step, approve-checkpoint, and reject-checkpoint require legacyChainControls: true.

subagent_wait blocks on background work: { all: true }, { id }, { timeoutMs }. Background runs are detached — prefer returning control and letting Pi deliver the completion notification, and use subagent_wait only when the current turn must have results before it ends. { id, nonBlocking: true } resolves the prefix once, returns a subscription token immediately, and wakes the session on completion/failure/attention/timeout. Headless sessions auto-drain current-session work at agent_end as a safeguard.

Agent Definition Files

Markdown with YAML frontmatter. Precedence low → high: builtin (~/.pi/agent/extensions/subagent/agents/), installed package (pi-subagents.agents or pi.subagents.agents in package.json), user (~/.pi/agent/agents/**/*.md), project (.pi/agents/**/*.md; legacy .agents/**/*.md is also read, project config wins collisions). agentScope: "user" | "project" | "both" controls discovery.

---
name: scout
package: code-analysis        # registers as code-analysis.scout
description: Fast codebase recon
aliases: explorer, code-scout
tools: read, grep, find, ls, bash, mcp:chrome-devtools
extensions:                   # omitted = all; empty = none; list = allowlist
subagentOnlyExtensions: ./tools/child-only-search.ts
model: claude-haiku-4-5
fallbackModels: openai/gpt-5-mini, anthropic/claude-sonnet-4
thinking: high
systemPromptMode: replace     # or append (keeps Pi's base prompt)
inheritProjectContext: false
inheritSkills: false
skills: safe-bash, review-checklist
skillPath: ./skills, ../shared-skills
defaultContext: fork
output: context.md
defaultReads: context.md
defaultProgress: true
async: true
timeoutMs: 900000
toolTimeoutMs: 600000
turnBudget: {"maxTurns":20,"graceTurns":2}
acceptance: {"level":"none","reason":"lightweight lookup"}
acceptanceRole: read-only     # or writer
completionGuard: false        # false for non-implementation validators
interactive: true             # parsed, not enforced
maxSubagentDepth: 1
memory: { scope: project, path: security-reviewer }
permission: { write: allow, edit: ask }
---
Your system prompt goes here.

Scalar list fields (tools, defaultReads, skills, skillPath, fallbackModels, extensions, subagentOnlyExtensions) accept comma-separated or YAML block-list form. Model ids match fuzzily (provider separator, id separator, case, trailing date stamps); a qualified provider query never switches providers.

Custom agents start with a clean prompt: they do not inherit Pi's base prompt, project instruction files, or the skills catalog unless systemPromptMode: append, inheritProjectContext: true, or inheritSkills: true.

Tool selection: omitting tools gives Pi's normal builtins; an explicit list is a strict allowlist; an empty field emits --no-tools. Allowlisting a name does not load the extension that registers it — load it through normal discovery, extensions, subagentOnlyExtensions, or a path-like tools entry. mcp: entries select direct MCP tools (requires pi-mcp-adapter; a global directTools: true is not sufficient, and an mcp: entry named subagent does not authorize nested fanout). Children never get the subagent tool unless their resolved builtin tools explicitly includes it. Missing providers fail the run before the first model turn.

Per-agent memory (memory: { scope: "project" | "user", path }) injects the first 200 lines of MEMORY.md from <project>/.pi/agent-memory/<path> or ~/.pi/agent/agent-memory/<path> into the child prompt. Agents with write tools are told they may append dated entries; read-only agents get a read-only block. Paths are validated against traversal and symlink escape, and the directory is created lazily by the agent's own write.

Refinement Overlays

/subagents-refine <agent> (or { action: "refine" }) layers bounded project-local guidance on one agent's system prompt without editing its file. It collects bounded evidence from that agent's recent project runs, then launches a fresh read-only proposal child to draft small guidance edits. Proposals are validated first — edits attempting to override safety, policy, tool, output, acceptance, developer, or system instructions are rejected, as are edits targeting all agents or base agent files. The overlay lands at .pi/subagents/refinements/<agent>.md with revision metadata and snapshots, and is injected at launch as a <pi-subagents-refinement> block scoped to the project. refine.show prints the overlay and history; refine.rollback restores the previous revision; deleting the file removes the refinement.

Settings

~/.pi/agent/settings.json or .pi/settings.json (project wins):

{
  "subagents": {
    "defaultModel": "deepseek-v4-flash",
    "defaultThinking": "medium",
    "defaultExtensions": [],
    "disableThinking": false,
    "disableBuiltins": false,
    "projectRootResolution": "git-root",
    "agentOverrides": {
      "reviewer": { "model": "anthropic/claude-sonnet-4", "thinking": "high", "fallbackModels": ["openai/gpt-5-mini"] }
    },
    "watchdog": { "enabled": true, "main": { "model": "anthropic/claude-opus-4-8", "thinking": "high" } },
    "modelScope": { "enforce": true, "strict": true, "allow": ["anthropic/*", "openai/gpt-5-*"] }
  }
}

Model precedence, strongest first: per-run override → agent frontmatter model → agentOverrides.<name>.model → subagents.defaultModel → the parent session model.

Override fields: description, model, fallbackModels, thinking, systemPromptMode, inheritProjectContext, inheritSkills, defaultContext, acceptanceRole, disabled, skills, tools, systemPrompt, extensions. Use false to clear an inherited defaultContext/acceptanceRole, and tools: "inherit" on a builtin to drop its bundled allowlist for Pi's normal builtins. Matching user and project agents also receive override fields their frontmatter leaves unset. disableThinking: true clears bundled builtin thinking defaults for providers that reject :level suffixes.

modelScope.allow is glob-matched (only * is special, case-insensitive) against the resolved provider/id. Explicitly passed models that match nothing error and abort; models from frontmatter, defaultModel, the inherited session model, or fallback chains only warn — unless strict: true, which rejects every out-of-scope resolved model and fails the run on an invalid fallback. enforce: true requires a non-empty allow.

projectRootResolution defaults to "nearest" (nearest parent with .pi or .agents); set "git-root" in the repository root .pi/settings.json so monorepos and worktrees anchor package discovery, project agents, and agentOverrides at the git worktree root.

Recommended model tiering: a cheap model at low thinking for recon/mechanical edits, a mid-tier at medium for most delegations, a top reasoning model at high only for hard tasks arriving with explicit completion criteria (they loop on vague goals), and an intent-reading model for ambiguous UX/product/planning work. Give intent-tier agents cross-provider fallbackModels so subscription limits degrade gracefully; note that forked context over an Anthropic parent forces child thinking off, so intent-tier agents work best with fresh context.

Profiles live in ~/.pi/agent/profiles/pi-subagents/ and cached provider catalogs in .../providers/. Workflow: /subagents-refresh-provider-models <provider> → /subagents-generate-profiles <provider> → /subagents-load-profile <provider>.quota; /subagents-check-profile re-checks assigned models against the registry and a live probe.

Extension Config

~/.pi/agent/extensions/subagent/config.json:

Environment: PI_SUBAGENT_MAX_DEPTH (nesting; default 2), PI_SUBAGENT_MAX_SPAWNS_PER_SESSION, PI_SUBAGENT_MAX_SPAWNS_PER_RUN, PI_SUBAGENT_TOOL_TIMEOUT_MS, PI_SUBAGENT_WAIT_TOOL_ENABLED, PI_SUBAGENT_PI_BINARY (override the child Pi launch command), PI_SUBAGENT_TASK_DELIVERY (auto default writes tasks over 8000 chars to a temp task.md; file always does, for hosts whose EDR kills children with long argv), PI_SUBAGENTS_WORKTREE_DIR. PI_SUBAGENT_DEPTH is internal — do not set it.

The worktree setup hook runs once per created worktree with an absolute, ~/, or repo-relative path (bare command names rejected). stdin is JSON with repoRoot, worktreePath, agentCwd, branch, index, runId, baseCommit; stdout must be one JSON object such as { "syntheticPaths": [".venv", ".env.local"] }, whose worktree-relative paths are removed before diff capture. Tracked files can never be marked synthetic. Default timeout 30000 ms.

Worktrees and Acceptance Gates

Set worktree: true on runs.run/runs.all items (or at the top level to make it the default, overridable per child with worktree: false) to give each writing child its own managed git worktree. Each branches from clean HEAD, journals ownership before launch, captures a patch and handoff manifest, then removes cleanly captured temporary worktrees and branches; the manifest path stays in the child's artifactPaths. Keep one writer when parallel writes are not intentionally isolated. action: "worktree.discard" requires the aggregate handoffPath.

{ agent: "worker", task: "Implement the fix", acceptance: {
  level: "verified",
  criteria: ["Patch the bug without widening scope"],
  evidence: ["changed-files", "tests-added", "commands-run", "residual-risks", "no-staged-files"],
  verify: [{ id: "focused", command: "npm test", timeoutMs: 120000 }]
} }

Levels are auto (default), none, attested, checked, and verified; review is a separate gate under acceptance.review. Inference: async, risky, and dynamic writer contexts get checked evidence plus review: { agent: "reviewer", required: true }; read-only tasks get lightweight attestation; normal writer tasks get checked evidence without review. acceptanceRole: "read-only" | "writer" in frontmatter or overrides guides inference for ambiguous tasks without changing tool access.

gate: "npm test" is shorthand for one host-run verification command (acceptance.level: "verified" with that single command). Results are memoized per tracked workspace state and effective environment, so an unchanged tree does not rerun it; with worktree: true it runs inside the child's worktree. gate cannot combine with acceptance and is rejected on retained resume items.

Evidence statuses: claimed, attested, checked, verified (runtime verification commands passed — child-reported success does not count), review-required, reviewed, rejected. Bare "none" is rejected (use { level: "none", reason }); "reviewed" is not a settable policy level. For attested or stricter, the child prompt asks for a fenced acceptance-report JSON block; fences are stripped from output artifacts while per-child metadata keeps the full acceptance ledger. Explicit failed gates fail the run; inferred gates stay observable without failing it.

Missions and Schedules

Ordinary workflow launches create one enclosing mission by default, stored under ~/.pi/agent/missions/projects/<project-hash>/ and linking objectives, run ids, lifecycle status, decisions, artifact paths, and delivery receipts. Children do not create separate missions. details.missionId is authoritative and human receipts end with Mission: <id> (<status>). Pass mission: false for an ephemeral workflow with no mission and no state global, or missions.enabled: false to disable automatic creation (explicit fields and actions still work). Automatic persistence failures are reported as details.missionWarning without blocking the run; explicit missionId/mission requests are strict before launch.

An explicit mission object needs exactly one non-empty title or summary (objective and labels optional). goal: true requires budget: { tokens } and turns the mission into a continuation driver: after each parent turn an idle goal mission emits one needs-attention notice with its title, remaining budget, and next ready action (from state.nextReadyAction, state.nextAction, a ready state item, an open decision, or linked-run state). Reaching the budget sets budget-exhausted and stops notices. The extension never launches or replans goal work itself.

state.get(key) / state.set(key, value) give a workflow durable JSON state through its mission, shared across later workflows attached with the same missionId. Each set takes the state-file lock and merges with the latest on-disk state; missing keys return undefined, and the whole state file is capped at 256 KiB.

Durable schedules are enabled by default under .pi/subagents/schedules/<id>/ (or scheduledRuns.storeRoot):

{ action: "schedule.create", id: "evening-review", name: "Evening review", at: "+30m",
  workflowScript: `return runs.run("main", { agent: "reviewer", task: "Review the current diff." })` }
{ action: "schedule.create", id: "backlog", every: "6h", catchUp: "latest", workflowScript: "..." }

Fixed intervals support m/h/d/w and advance from the planned time without completion drift. Scheduled runs always launch async with fresh context and disable automatic mission creation. overlap is fixed to skip; catchUp supports latest (default) and none; schedule.run-due lets an external launcher start due work without making pi-subagents a daemon. Calendar/cron recurrence, queue/replace overlap, and a schedule TUI inspector are deferred.

For substantial work in another codebase, prefer a Herdr project pane (project.open) over ordinary child nesting; use an explicit cwd only for small bounded cross-project work.

Watchdog and Child Permissions

The watchdog is an opt-in adversarial reviewer for repo edits — not the reviewer agent, and not configured by defaultModel/agentOverrides.reviewer. It runs at the agent_end boundary only when the repo's final state changed during the turn; multiple edits coalesce into one review, unchanged/reverted diffs are skipped, and .pi/subagents//tmp/ artifacts do not trigger it. In orchestrated runs each writing child can review its own worktree while the parent reviews the aggregate diff.

Use a strong complementary model: /subagents-watchdog recommend-model (current policy is Opus 4.8 high or GPT 5.5 high — use whichever your main session is not). session model recommended changes only this session; model recommended saves to settings without enabling. Settings keys: watchdog.main.model/.thinking (omitting main.model uses the session model; setting it without a thinking suffix runs with thinking off), watchdog.children.model, watchdog.children.overrides.<agent>.model.

Scope monitoring keeps a bounded in-memory current-scope artifact from real user prompts and prepends it to review input (watchdog.scope.enabled), so the reviewer can flag scope-drift; newer prompts supersede older ones and watchdog auto-follow prompts are not recorded as scope. watchdog.cadence.everyNTools adds Scopey-style non-blocking reviews every N tool results, delivered transcript-visibly via steer after the current tool boundary — pick a cheap model for frequent monitoring. watchdog.autoFollow (blockers, maxAttempts, stalemateRepeats) can queue a visible follow-up asking the agent to address a blocker, stopping on repeated identical blockers.

LSP diagnostics: when enabled, the watchdog checks changed TypeScript/JavaScript files for fresh language-server diagnostics before the model review, auto-detecting typescript-language-server from node_modules/.bin or PATH (never installing anything or scanning the workspace). Errors become blockers, warnings concerns; bound with watchdog.lsp.enabled, timeoutMs, maxFiles, maxDiagnostics.

Native child permissions are opt-in and apply only to Pi child runtimes. Configure non-bash rules under permissions.rules in the extension config ("read": "allow", "write": "ask", "edit": "deny"), overridable by an agent's permission:/permissions: frontmatter block. Omitted and unknown tools default to allow, explicit allow removes an inherited restriction, and the gate is not registered when no ask/deny rule resolves. An ask pauses that exact call and sends a bounded, redacted preview to a one-call arbiter owned by the child watchdog, which returns only approve/deny — enable and configure subagents.watchdog.children first, since a disabled watchdog, missing model/auth, timeout, or malformed response denies the call. Decisions are written to bounded audit JSONL with decisionSource: "watchdog". bash is always passed through and bash rules are rejected rather than parsed — use pi-guard for command-level policy. External CLI profiles are opaque processes, so a launch with effective ask/deny rules is rejected rather than claiming enforcement.

Supervisor Coordination

Native, no pi-intercom required: children call contact_supervisor({ reason, message }) with reason ∈ need_decision, interview_request, progress_update; the parent replies with subagent_supervisor({ action: "reply", replyTo, message }) or checks { action: "pending" }. Requests are scoped to the exact Pi session id that spawned the child, so a second Pi session in the same repository does not receive them. If no external pi-intercom owns the name, the native channel also exposes intercom as a compatibility fallback. A foreground child may detach while awaiting a reply: reply first, then subagent_wait({ id: runId }). Children should not ask for clarification when the only conflict is review-only/no-edit versus progress- or artifact-writing instructions — no-edit wins.

Child-safety boundaries are enforced at runtime: spawned children never receive the bundled pi-subagents skill; forked child context is filtered to strip parent-only orchestration instructions, slash/status/control messages, and prior parent subagent tool history; and children get boundary instructions that they are not the orchestrator. The exception is an agent whose resolved builtin tools includes subagent, which gets a child-safe tool bounded by maxSubagentDepth.

Observability

FleetView below the editor (or above, via fleetViewPlacement) keeps active work visible as a compact summary; with the editor empty, ↓/← expands it into main plus active children with agent, state, elapsed time, and token totals, ↑↓/jk selects, and Enter inspects. /subagents-fleet opens the live inspector: Shift+K/Shift+J scroll a line, PgUp/PgDn a page, x/Ctrl+O toggle tool details, r refresh, Esc close, s compose an acknowledged message to a live async child (Tab cycles steer/follow_up/auto), D stop after confirmation, H open a Herdr inspector pane (Herdr 0.7.5+). Ctrl+Alt+F opens it mid-turn. Successful background completions stay quiet so inactive tabs are not marked unread; failures and pauses notify immediately.

Async runs write lifecycle artifacts under <tmpdir>/pi-subagents-<scope>/async-subagent-runs/<id>/: status.json, events.jsonl, output-<n>.log, subagent-log-<runId>.md, with the final summary as <runId>.json in Pi's results directory (details.asyncDir points at the run directory). Stable v1 status fields: lifecycleArtifactVersion, runId/id, sessionId, mode, state, timestamps, durationMs, cwd, asyncDir, sessionFile, outputFile, workflowGraph, steps, results, totalTokens, totalCost, model/attemptedModels/modelAttempts, toolCount, turnCount, optional launchResolvedExtensions and runtimeAcknowledgedExtensions, and nested children. Read these files rather than scraping terminal output, and ignore unknown fields.

The result file is consumed and deleted once its completion notice is delivered; before deletion the watcher writes a versioned replay record under <resultsDir>/completion-replay/<runId>.json and a bounded output archive under <resultsDir>/output-archives/<runId>.json (64 KiB of result tail when no child output/session file exists). subagent_wait surfaces a slim projection in details.completions. Lifecycle artifact v3 adds process-terminal-candidate.json and process-terminal.json; a proof is observed only when the live parent saw the runner's close event, every recorded child writer has a close record, and any tracked session lease is free — otherwise unknown. Never infer exit from endedAt, result-file existence, PID disappearance, or lease absence.

Child-protocol bounds: a child JSONL line above 16 MiB fails with protocolError code protocol_output_limit (oversized turn_end/agent_end aggregates are replaced with bounded lifecycle records while preserving agent_end.willRetry); stderr retains its latest 128 KiB; agent_settled is the terminal watermark on current Pi builds.

Debug artifacts live under {sessionDir}/subagent-artifacts/, .pi/subagents/artifacts/ for project-scoped runs, or a temp dir: {runId}_{agent}_input.md, _output.md, .jsonl, _meta.json (timing, usage, exit code, final/attempted models, fallback outcomes, resolved acceptance ledger). For npm package projects, project-scoped artifacts need a .npmignore/files rule — pi-subagents warns when package settings could publish .pi/subagents/.

Extension Integration

Versioned in-process event-bus RPC: listen for subagents:rpc:v1:ready, emit on subagents:rpc:v1:request ({ version: 1, requestId, method, params }), read subagents:rpc:v1:reply:<requestId>. Methods: ping, status, spawn (requires workflowScript, async-only), steer, interrupt, stop, resume. ping.capabilities advertises events.asyncComplete, launchResolvedExtensions, runtimeAcknowledgedExtensions, processTerminalProof, nonRecoveringSteer, resume, and fleetStatus: { version: 1 } (successful status replies then include a bounded data.fleet DTO that never exposes run, async, or tool IDs). RPC steering disables pause-and-revive recovery so the caller keeps authority over the child it spawned.

Also exported:

• pi-subagents/preflight — resolveSubagentLaunchContract(...) resolves an ordinary single-agent launch contract side-effect-free (agent identity and shadowed candidates, parsed-definition digest, context/model/tools/skills/MCP/extensions, artifact and async paths, capability-ceiling audit data, launchContractDigest). Failure codes: missing_agent, ambiguous_agent, missing_skill, denied_required_tool, invalid_artifact_dir, invalid_cwd, unsupported_mode; host-only facts appear as host_required diagnostics.
• pi-subagents/delegation — SUBAGENT_DELEGATION_REQUEST_EVENT / SUBAGENT_DELEGATION_RESPONSE_EVENT run one configured foreground leaf agent. ownerRunId + nodeId is the logical identity (requestId is one attempt; a second active attempt gets duplicate_node), result mode is explicit (text stays literal, structured returns schema-validated JSON), schemas cap at 64 KiB and values at 1 MiB. Foreground-only; requires an active extension context.
• pi-subagents/capability-ceiling — registerSubagentCapabilityCeiling({ sessionId, source, ceiling }) enforces a session-scoped ceiling (allowedAgents, allowedTools, denyExtensions). Active registrations intersect allowlists and OR denyExtensions; non-allowlisted agents fail before spawn and stay visible in list as non-executable; the snapshot propagates monotonically to nested/async children.
• pi-subagents/background-work — registerBackgroundWorkProvider({ name, wakeChannels, listActiveWork, reconcile }) makes another extension's jobs visible to subagent_wait, keyed by stable provider-local id plus owning session id.
• pi-subagents/project-panes — PROJECT_PANES_API_VERSION (currently 1), openProjectPane, getProjectPaneStatus, closeProjectPane.

Bus events: subagent:async-started (payload includes truncated task and workflow-level goal), subagent:async-complete, subagent:control-intercom, subagent:result-intercom, subagent:process-terminal, plus child-emitted subagent:acknowledge-extension. pi.events is in-process only — use file artifacts or pi-intercom across processes.

Herdr integration: when HERDR_ENV=1 and HERDR_PANE_ID are set, pi-subagents reports active async-run counts through pane metadata, emits herdr:blocked/herdr:busy, and restores state after /reload or /resume. Herdr 0.7.5+ adds on-demand inspector panes (inspector.open/status/close, a raw dashboard reading lifecycle artifacts — closing it never stops the run) and project panes (project.open/status/close, a Pi session rooted in another repo that owns its own subagents; bindings at <projectRoot>/.pi/subagents/project-panes/herdr.json).

Skills and the Bundled Skill

Skills are SKILL.md files selected per agent; discovery is project-first (project config skills/, project/task packages, project settings, ~/.pi/agent/skills/, user packages, user settings). Set them via agent defaults, per-run skill: "tmux, safe-bash", or skill: false; top-level skill in a chain is additive and a step-level value overrides. Missing skills warn instead of failing. When an agent has an explicit tools allowlist plus resolved skills, read is added so skill files can be loaded. Agent-local skillPath candidates never enter Pi's global catalog — pair inheritSkills: false with explicit skills and skillPath for a child that should receive only its private skills.

The package bundles a pi-subagents skill for the orchestrating parent only, covering delegation patterns, prompt-workflow recipes, role-agent prompting, safety boundaries, intercom conventions, and control/diagnostics.

External CLI Runners

An agent profile can run a local one-shot command instead of a Pi child:

runner:
  type: external-cli
  command: node
  args: ["./scripts/local-reviewer.mjs"]
  promptDelivery: stdin
async: true

They are async-only, receive one combined system/task prompt over stdin, and use argv arrays without a shell. Supported: status artifacts, stdout/stderr logs, timeout, stop (full output goes to log files; in-memory final stdout/stderr keep the last 64 KiB). Not supported: foreground/clarify, steer/resume/interrupt-as-pause, Pi models/tools/extensions, skills, structured output, nested subagents, fallback models, and native permission enforcement.

Recursion Guard

Subagents can call subagent only when their resolved builtin tools explicitly include it — intended for delegated fanout agents, not ordinary workers or reviewers. Nesting defaults to two levels (main → subagent → sub-subagent); deeper calls are blocked with guidance to finish directly. Nested runs appear in the parent status tree, and status, interrupt, and resume can target one by its nested id. Configure with PI_SUBAGENT_MAX_DEPTH, config.maxSubagentDepth, or agent frontmatter (which can only tighten).

Session Sharing

share: true exports the full session to HTML, uploads it to a secret GitHub Gist through your gh credentials, and returns a https://shittycodingagent.ai/session/?<gistId> URL. Disabled by default — session data may contain source code, paths, environment variables, or credentials.