Pi Interactive Shell

Foreground subagents run in an overlay where the user watches (and can intervene). Use interactive_shell with mode: "hands-free" to monitor while receiving periodic updates, or mode: "dispatch" to be notified on completion without polling.

Dispatch subagents also use interactive_shell but with mode: "dispatch". The agent fires the session and moves on. When the session completes, the agent is woken up via triggerTurn with the output in context. Add background: true for headless execution (no overlay).

Background subagents run invisibly via the subagent tool. Pi-only, but captures full output and supports parallel execution.

When to Use Foreground Subagents

Use interactive_shell (foreground) when:

• The task is long-running and the user should see progress
• The user might want to intervene or guide the agent
• You want hands-free monitoring with periodic status updates
• You need a different agent's capabilities (only if user specifies)

Use subagent (background) when:

• You need parallel execution of multiple tasks
• You want full output capture for processing
• The task is quick and deterministic
• User doesn't need to see the work happening

Default Agent Choice

Default to pi for foreground subagents unless the user explicitly requests a different agent:

Pi is the default because it's already available, has the same capabilities, and maintains consistency. Only use Claude, Gemini, Codex, or other agents when the user specifically asks for them.

Structured Spawn and /spawn

For Pi, Codex, and Claude, prefer structured spawn params when you want the extension's shared resolver, config defaults, native startup prompt forms, or Pi-only fork/worktree behavior:

interactive_shell({ spawn: { agent: "pi" }, mode: "interactive" })
interactive_shell({ spawn: { agent: "codex" }, mode: "dispatch" })
interactive_shell({ spawn: { agent: "claude", prompt: "Review the diffs" }, mode: "dispatch" })
interactive_shell({ spawn: { agent: "claude", worktree: true }, mode: "hands-free" })
interactive_shell({ spawn: { mode: "fork" }, mode: "interactive" }) // Pi-only

Structured spawn uses the same resolver and defaults as the user-facing /spawn command. Raw command is still the right choice for arbitrary CLIs and custom launch strings.

For users in chat, /spawn now supports the configured default agent plus explicit overrides like /spawn codex, /spawn claude, /spawn pi, /spawn fork, and /spawn pi fork. Add --worktree to run in a separate git worktree.

Quoted prompt text plus --hands-free or --dispatch turns /spawn into a monitored delegated run instead of a plain interactive overlay:

/spawn claude "review the diffs" --dispatch
/spawn codex "fix the failing tests" --hands-free
/spawn pi fork "continue from here" --dispatch

Foreground Subagent Modes

Interactive (default)

User has full control, types directly into the agent.

interactive_shell({ command: 'pi' })

Interactive with Initial Prompt

Agent starts working immediately, user supervises.

interactive_shell({ command: 'pi "Review this codebase for security issues"' })

Dispatch (Fire-and-Forget) - NON-BLOCKING, NO POLLING

Agent fires a session and moves on. Notified automatically on completion via triggerTurn.

// Start session - returns immediately, no polling needed
interactive_shell({
  command: 'pi "Fix all TypeScript errors in src/"',
  mode: "dispatch",
  reason: "Fixing TS errors"
})
// Returns: { sessionId: "calm-reef", mode: "dispatch" }
// → Do other work. When session completes, you receive notification with output.

Dispatch defaults autoExitOnQuiet: true. The agent can still query the sessionId if needed, but doesn't have to.

For fire-and-forget delegated runs (including QA-style delegated checks), prefer dispatch as the default mode.

Background Dispatch (Headless)

No overlay opens. Multiple headless dispatches can run concurrently:

interactive_shell({
  command: 'pi "Fix lint errors"',
  mode: "dispatch",
  background: true
})
// → No overlay. User can /attach to watch. Agent notified on completion.

Hands-Free (Foreground Subagent) - NON-BLOCKING

Agent works autonomously, returns immediately with sessionId. You query for status/output and kill when done.

// 1. Start session - returns immediately
interactive_shell({
  command: 'pi "Fix all TypeScript errors in src/"',
  mode: "hands-free",
  reason: "Fixing TS errors"
})
// Returns: { sessionId: "calm-reef", status: "running" }

// 2. Check status and get new output
interactive_shell({ sessionId: "calm-reef" })
// Returns: { status: "running", output: "...", runtime: 30000 }

// 3. When you see task is complete, kill session
interactive_shell({ sessionId: "calm-reef", kill: true })
// Returns: { status: "killed", output: "final output..." }

This is the primary pattern for foreground subagents - you delegate to pi (or another agent), query for progress, and decide when the task is done.

Hands-Free Workflow

Starting a Session

const result = interactive_shell({
  command: 'codex "Review this codebase"',
  mode: "hands-free"
})
// result.details.sessionId = "calm-reef"
// result.details.status = "running"

The user sees the overlay immediately. You get control back to continue working. If the user types to take over a monitored hands-free or dispatch session, they can press Ctrl+G to return control to the agent.

Querying Status

interactive_shell({ sessionId: "calm-reef" })

Returns:

• status: "running" | "user-takeover" | "exited" | "killed" | "backgrounded"
• output: Last 20 lines of rendered terminal (clean, no TUI animation noise)
• runtime: Time elapsed in ms

Rate limited: Queries are limited to once every 60 seconds. If you query too soon, the tool will automatically wait until the limit expires before returning. The user is watching the overlay in real-time - you're just checking in periodically.

Ending a Session

interactive_shell({ sessionId: "calm-reef", kill: true })

Kill when you see the task is complete in the output. Returns final status and output.

Fire-and-Forget Tasks

For single-task delegations where you don't need multi-turn interaction, enable auto-exit so the session kills itself when the agent goes quiet:

interactive_shell({
  command: 'pi "Review this codebase for security issues. Save your findings to /tmp/security-review.md"',
  mode: "hands-free",
  reason: "Security review",
  handsFree: { autoExitOnQuiet: true }
})
// Session auto-kills after ~8s of quiet (after the startup grace period)
// Read results from file:
// read("/tmp/security-review.md")

Instruct subagent to save results to a file since the session closes automatically.

Multi-Turn Sessions (default)

For back-and-forth interaction, leave auto-exit disabled (the default). Query status and kill manually when done:

interactive_shell({
  command: 'cursor-agent -f',
  mode: "hands-free",
  reason: "Interactive refactoring"
})

// Send follow-up prompts
interactive_shell({ sessionId: "calm-reef", input: "Now fix the tests", submit: true })

// Kill when done
interactive_shell({ sessionId: "calm-reef", kill: true })

Sending Input

interactive_shell({ sessionId: "calm-reef", input: "/help", submit: true })
interactive_shell({ sessionId: "calm-reef", inputKeys: ["ctrl+c"] })
interactive_shell({ sessionId: "calm-reef", inputPaste: "multi\nline\ncode" })
interactive_shell({ sessionId: "calm-reef", input: "y", inputKeys: ["enter"] })  // combine text + keys

Query Output

Status queries return rendered terminal output (what's actually on screen), not raw stream:

• Default: 20 lines, 5KB max per query
• No TUI animation noise (spinners, progress bars, etc.)
• Configurable via outputLines (max: 200) and outputMaxChars (max: 50KB)

// Get more output when reviewing a session
interactive_shell({ sessionId: "calm-reef", outputLines: 50 })

// Get even more for detailed review
interactive_shell({ sessionId: "calm-reef", outputLines: 100, outputMaxChars: 30000 })

Incremental Reading

Use incremental: true to paginate through output without re-reading:

// First call: get first 50 lines
interactive_shell({ sessionId: "calm-reef", outputLines: 50, incremental: true })
// → { output: "...", hasMore: true }

// Next call: get next 50 lines (server tracks position)
interactive_shell({ sessionId: "calm-reef", outputLines: 50, incremental: true })
// → { output: "...", hasMore: true }

// Keep calling until hasMore: false
interactive_shell({ sessionId: "calm-reef", outputLines: 50, incremental: true })
// → { output: "...", hasMore: false }

The server tracks your read position - just keep calling with incremental: true to get the next chunk.

Reviewing Output

Query sessions to see progress. Increase limits when you need more context:

// Default: last 20 lines
interactive_shell({ sessionId: "calm-reef" })

// Get more lines when you need more context
interactive_shell({ sessionId: "calm-reef", outputLines: 50 })

// Get even more for detailed review
interactive_shell({ sessionId: "calm-reef", outputLines: 100, outputMaxChars: 30000 })

Sending Input to Active Sessions

Use the sessionId from updates to send input to a running hands-free session:

Basic Input

// Send text and submit it
interactive_shell({ sessionId: "shell-1", input: "/help", submit: true })

// Send text with keys
interactive_shell({ sessionId: "shell-1", input: "/model", inputKeys: ["enter"] })

// Navigate menus
interactive_shell({ sessionId: "shell-1", inputKeys: ["down", "down", "enter"] })

// Interrupt
interactive_shell({ sessionId: "shell-1", inputKeys: ["ctrl+c"] })

Named Keys

Note: ic/dc, ppage/npage, bspace are tmux-style aliases for compatibility.

Modifier Combinations

Supports ctrl+, alt+, shift+ prefixes (or shorthand c-, m-, s-):

// Cancel
inputKeys: ["ctrl+c"]

// Alt+Tab
inputKeys: ["alt+tab"]

// Ctrl+Alt+Delete
inputKeys: ["ctrl+alt+delete"]

// Shorthand syntax
inputKeys: ["c-c", "m-x", "s-tab"]

Hex Bytes (Advanced)

Send raw escape sequences:

inputHex: ["0x1b", "0x5b", "0x41"]  // ESC[A (up arrow)

Bracketed Paste

Paste multiline text without triggering autocompletion/execution:

inputPaste: "function foo() {\n  return 42;\n}"

Model Selection Example

// Step 1: Open model selector
interactive_shell({ sessionId: "shell-1", input: "/model", inputKeys: ["enter"] })

// Step 2: Filter and select (after ~500ms delay)
interactive_shell({ sessionId: "shell-1", input: "sonnet", inputKeys: ["enter"] })

// Or navigate with arrows:
interactive_shell({ sessionId: "shell-1", inputKeys: ["down", "down", "down", "enter"] })

Context Compaction

interactive_shell({ sessionId: "shell-1", input: "/compact", submit: true })

For editor-based TUIs like pi, raw input only types text. It does not submit the prompt. Prefer submit: true or inputKeys: ["enter"] instead of relying on \n.

Changing Update Settings

Adjust timing during a session:

// Change max interval (fallback for on-quiet mode)
interactive_shell({ sessionId: "calm-reef", settings: { updateInterval: 120000 } })

// Change quiet threshold (how long to wait after output stops)
interactive_shell({ sessionId: "calm-reef", settings: { quietThreshold: 3000 } })

// Both at once
interactive_shell({ sessionId: "calm-reef", settings: { updateInterval: 30000, quietThreshold: 2000 } })

CLI Quick Reference

Gemini model: gemini -m gemini-3-flash-preview -i "prompt"

Prompt Packaging Rules

The reason parameter is UI-only - it's shown in the overlay header but NOT passed to the subprocess.

To give the agent an initial prompt, embed it in the command:

// WRONG - agent starts idle, reason is just UI text
interactive_shell({ command: 'claude', reason: 'Review the codebase' })

// RIGHT - agent receives the prompt
interactive_shell({ command: 'claude "Review the codebase"', reason: 'Code review' })

Handoff Options

Transfer (Ctrl+T) - Recommended

When the subagent finishes, the user presses Ctrl+T to transfer output directly to you:

[Subagent finishes work in overlay]
        ↓
[User presses Ctrl+T]
        ↓
[You receive: "Session output transferred (150 lines):
  
  Completing skill integration...
  Modified files:
  - skills.ts
  - agents/types/..."]

This is the cleanest workflow - the subagent's response becomes your context automatically.

Configuration: transferLines (default: 200), transferMaxChars (default: 20KB)

Tail Preview (default)

Last 30 lines included in tool result. Good for seeing errors/final status.

Snapshot to File

Write full transcript to ~/.pi/agent/cache/interactive-shell/snapshot-*.log:

interactive_shell({
  command: 'claude "Fix bugs"',
  handoffSnapshot: { enabled: true, lines: 200 }
})

Artifact Handoff (for complex tasks)

Instruct the delegated agent to write a handoff file:

Write your findings to .pi/delegation/claude-handoff.md including:
- What you did
- Files changed
- Any errors
- Next steps for the main agent

Safe TUI Capture

Never run TUI agents via bash - they hang even with --help. Use interactive_shell with timeout instead:

interactive_shell({
  command: "pi --help",
  mode: "hands-free",
  timeout: 5000  // Auto-kill after 5 seconds
})

The process is killed after timeout and captured output is returned in the handoff preview. This is useful for:

• Getting CLI help from TUI applications
• Capturing output from commands that don't exit cleanly
• Any TUI command where you need quick output without user interaction

For pi CLI documentation, you can also read directly: /opt/homebrew/lib/node_modules/@mariozechner/pi-coding-agent/README.md

Background Session Management

// Background an active session (close overlay, keep running)
interactive_shell({ sessionId: "calm-reef", background: true })

// List all background sessions
interactive_shell({ listBackground: true })

// Reattach to a background session
interactive_shell({ attach: "calm-reef" })                    // interactive (blocking)
interactive_shell({ attach: "calm-reef", mode: "hands-free" })  // hands-free (poll)
interactive_shell({ attach: "calm-reef", mode: "dispatch" })    // dispatch (notified)

// Dismiss background sessions (kill running, remove exited)
interactive_shell({ dismissBackground: true })               // all
interactive_shell({ dismissBackground: "calm-reef" })        // specific

Quick Reference

Dispatch subagent (fire-and-forget, default to pi):

interactive_shell({
  command: 'pi "Implement the feature described in SPEC.md"',
  mode: "dispatch",
  reason: "Implementing feature"
})
// Returns immediately. You'll be notified when done.

Background dispatch (headless, no overlay):

interactive_shell({
  command: 'pi "Fix lint errors"',
  mode: "dispatch",
  background: true,
  reason: "Fixing lint"
})

Start foreground subagent (hands-free, default to pi):

interactive_shell({
  command: 'pi "Implement the feature described in SPEC.md"',
  mode: "hands-free",
  reason: "Implementing feature"
})
// Returns sessionId in updates, e.g., "shell-1"

Send input to active session:

// Text with enter
interactive_shell({ sessionId: "calm-reef", input: "/compact", submit: true })

// Text + named keys
interactive_shell({ sessionId: "calm-reef", input: "/model", inputKeys: ["enter"] })

// Menu navigation
interactive_shell({ sessionId: "calm-reef", inputKeys: ["down", "down", "enter"] })

Change update frequency:

interactive_shell({ sessionId: "calm-reef", settings: { updateInterval: 60000 } })

Foreground subagent (user requested different agent):

interactive_shell({
  command: 'claude "Review this code for security issues"',
  mode: "hands-free",
  reason: "Security review with Claude"
})

Background subagent:

subagent({ agent: "scout", task: "Find all TODO comments" })