pi_harness/packages/coding-agent/examples/extensions

Extension Examples

Example extensions for pi-coding-agent.

Usage

# Load an extension with --extension flag
pi --extension examples/extensions/permission-gate.ts

# Or copy to extensions directory for auto-discovery
cp permission-gate.ts ~/.pi/agent/extensions/

Examples

Lifecycle & Safety

Extension	Description
permission-gate.ts	Prompts for confirmation before dangerous bash commands (rm -rf, sudo, etc.)
protected-paths.ts	Blocks writes to protected paths (.env, .git/, node_modules/)
confirm-destructive.ts	Confirms before destructive session actions (clear, switch, branch)
dirty-repo-guard.ts	Prevents session changes with uncommitted git changes

Custom Tools

Extension	Description
todo.ts	Todo list tool + /todos command with custom rendering and state persistence
hello.ts	Minimal custom tool example
question.ts	Demonstrates ctx.ui.select() for asking the user questions
subagent/	Delegate tasks to specialized subagents with isolated context windows

Commands & UI

Extension	Description
preset.ts	Named presets for model, thinking level, tools, and instructions via --preset flag and /preset command
plan-mode.ts	Claude Code-style plan mode for read-only exploration with /plan command
tools.ts	Interactive /tools command to enable/disable tools with session persistence
handoff.ts	Transfer context to a new focused session via /handoff <goal>
qna.ts	Extracts questions from last response into editor via ctx.ui.setEditorText()
status-line.ts	Shows turn progress in footer via ctx.ui.setStatus() with themed colors
snake.ts	Snake game with custom UI, keyboard handling, and session persistence
send-user-message.ts	Demonstrates pi.sendUserMessage() for sending user messages from extensions
timed-confirm.ts	Demonstrates AbortSignal for auto-dismissing ctx.ui.confirm() and ctx.ui.select() dialogs

Git Integration

Extension	Description
git-checkpoint.ts	Creates git stash checkpoints at each turn for code restoration on branch
auto-commit-on-exit.ts	Auto-commits on exit using last assistant message for commit message

System Prompt & Compaction

Extension	Description
pirate.ts	Demonstrates systemPromptAppend to dynamically modify system prompt
custom-compaction.ts	Custom compaction that summarizes entire conversation

External Dependencies

Extension	Description
chalk-logger.ts	Uses chalk from parent node_modules (demonstrates jiti module resolution)
with-deps/	Extension with its own package.json and dependencies
file-trigger.ts	Watches a trigger file and injects contents into conversation

Writing Extensions

See docs/extensions.md for full documentation.

import type { ExtensionAPI } from "@mariozechner/pi-coding-agent";
import { Type } from "@sinclair/typebox";

export default function (pi: ExtensionAPI) {
  // Subscribe to lifecycle events
  pi.on("tool_call", async (event, ctx) => {
    if (event.toolName === "bash" && event.input.command?.includes("rm -rf")) {
      const ok = await ctx.ui.confirm("Dangerous!", "Allow rm -rf?");
      if (!ok) return { block: true, reason: "Blocked by user" };
    }
  });

  // Register custom tools
  pi.registerTool({
    name: "greet",
    label: "Greeting",
    description: "Generate a greeting",
    parameters: Type.Object({
      name: Type.String({ description: "Name to greet" }),
    }),
    async execute(toolCallId, params, onUpdate, ctx, signal) {
      return {
        content: [{ type: "text", text: `Hello, ${params.name}!` }],
        details: {},
      };
    },
  });

  // Register commands
  pi.registerCommand("hello", {
    description: "Say hello",
    handler: async (args, ctx) => {
      ctx.ui.notify("Hello!", "info");
    },
  });
}

Key Patterns

Use StringEnum for string parameters (required for Google API compatibility):

import { StringEnum } from "@mariozechner/pi-ai";

// Good
action: StringEnum(["list", "add"] as const)

// Bad - doesn't work with Google
action: Type.Union([Type.Literal("list"), Type.Literal("add")])

State persistence via details:

// Store state in tool result details for proper branching support
return {
  content: [{ type: "text", text: "Done" }],
  details: { todos: [...todos], nextId },  // Persisted in session
};

// Reconstruct on session events
pi.on("session_start", async (_event, ctx) => {
  for (const entry of ctx.sessionManager.getBranch()) {
    if (entry.type === "message" && entry.message.toolName === "my_tool") {
      const details = entry.message.details;
      // Reconstruct state from details
    }
  }
});