feat(hook): add pi support

docs/guide/getting-started/supported-agents.md

@@ -35,6 +35,7 @@ Agent runs "cargo test"
 | Gemini CLI | Rust binary (`BeforeTool`) | Yes |
 | OpenCode | TypeScript plugin (`tool.execute.before`) | Yes |
 | OpenClaw | TypeScript plugin (`before_tool_call`) | Yes |
+| Pi | TypeScript extension (`tool_call` event) | Yes |
 | Hermes | Python plugin (`terminal` command mutation) | Yes |
 | Cline / Roo Code | Rules file (prompt-level) | N/A |
 | Windsurf | Rules file (prompt-level) | N/A |
@@ -85,6 +86,27 @@ rtk init --global --opencode
 
 Creates `~/.config/opencode/plugins/rtk.ts`. Uses the `tool.execute.before` hook.
 
+### Pi
+
+```bash
+# Project-local (default)
+rtk init --agent pi
+
+# Global — all projects
+rtk init --agent pi --global
+```
+
+Creates `.pi/extensions/rtk.ts` (local) or `~/.pi/agent/extensions/rtk.ts` (global). Pi auto-discovers extensions from both paths on startup.
+
+Uninstall:
+
+```bash
+rtk init --uninstall --agent pi
+rtk init --uninstall --agent pi --global
+```
+
+Removes only the installed Pi extension file.
+
 ### OpenClaw
 
 ```bash
@@ -151,7 +173,7 @@ Support is blocked on upstream `BeforeToolCallback` ([mistral-vibe#531](https://
 | **Plugin** | TypeScript, JavaScript, or Python in agent's plugin system | Transparent, in-place mutation when the agent allows it |
 | **Rules file** | Prompt-level instructions | Guidance only — agent is told to prefer `rtk <cmd>` |
 
-Rules file integrations (Cline, Windsurf, Codex, Kilo Code, Antigravity) rely on the model following instructions. Full hook integrations (Claude Code, Cursor, Gemini) are guaranteed — the command is rewritten before the agent sees it.
+Rules file integrations (Cline, Windsurf, Codex, Kilo Code, Antigravity) rely on the model following instructions. Full hook integrations (Claude Code, Cursor, Gemini) are guaranteed — the command is rewritten before the agent sees it. Plugin integrations (OpenCode, Pi) use in-place mutation via the agent's TypeScript extension API.
 
 ## Windows support
 

hooks/README.md

@@ -4,7 +4,7 @@
 
 **Deployed hook artifacts** — the actual files installed on user machines by `rtk init`. These are shell scripts, TypeScript plugins, and rules files that run outside the Rust binary. They are **thin delegates**: parse agent-specific JSON, call `rtk rewrite` as a subprocess, format agent-specific response. Zero filtering logic lives here.
 
-Owns: per-agent hook scripts and configuration files for 8 supported agents (Claude Code, Copilot, Cursor, Cline, Windsurf, Codex, OpenCode, Hermes).
+Owns: per-agent hook scripts and configuration files for 9 supported agents (Claude Code, Copilot, Cursor, Cline, Windsurf, Codex, OpenCode, Hermes, Pi).
 
 Does **not** own: hook installation/uninstallation (that's `src/hooks/init.rs`), the rewrite pattern registry (that's `discover/registry`), or integrity verification (that's `src/hooks/integrity.rs`).
 
@@ -40,6 +40,7 @@ Each agent subdirectory has its own README with hook-specific details:
 - **[`windsurf/`](windsurf/README.md)** — Rules file (prompt-level), `.windsurfrules` workspace-scoped
 - **[`codex/`](codex/README.md)** — Awareness document, `AGENTS.md` integration, `$CODEX_HOME` or `~/.codex/` location
 - **[`opencode/`](opencode/README.md)** — TypeScript plugin, `zx` library, `tool.execute.before` event, in-place mutation
+- **[`pi/`](pi/README.md)** — TypeScript extension, `tool_call` event, `isToolCallEventType` guard, in-place mutation, `~/.pi/agent/extensions/`
 - **[`hermes/`](hermes/README.md)** — Python plugin, `pre_tool_call` hook, in-place terminal command mutation
 
 ## Supported Agents
@@ -55,13 +56,15 @@ Each agent subdirectory has its own README with hook-specific details:
 | Windsurf | Custom instructions (rules file) | Prompt-level guidance | N/A |
 | Codex CLI | AGENTS.md / instructions | Prompt-level guidance | N/A |
 | OpenCode | TypeScript plugin (`tool.execute.before`) | In-place mutation | Yes |
+| Pi | TypeScript extension (`tool_call` event) | In-place mutation | Yes |
 | Hermes | Python plugin (`pre_tool_call`) | In-place mutation | Yes |
 
 ## JSON Formats by Agent
 
 ### Claude Code (Shell Hook)
 
 **Input** (stdin):
+
 ```json
 {
   "tool_name": "Bash",
@@ -70,6 +73,7 @@ Each agent subdirectory has its own README with hook-specific details:
 ```
 
 **Output** (stdout, when rewritten):
+
 ```json
 {
   "hookSpecificOutput": {
@@ -86,6 +90,7 @@ Each agent subdirectory has its own README with hook-specific details:
 **Input**: Same as Claude Code.
 
 **Output** (stdout, when rewritten):
+
 ```json
 {
   "permission": "allow",
@@ -98,6 +103,7 @@ Returns `{}` when no rewrite (Cursor requires JSON for all paths).
 ### Copilot CLI (Rust Binary)
 
 **Input** (stdin, camelCase, `toolArgs` is JSON-stringified):
+
 ```json
 {
   "toolName": "bash",
@@ -106,6 +112,7 @@ Returns `{}` when no rewrite (Cursor requires JSON for all paths).
 ```
 
 **Output** (no `updatedInput` support -- uses deny-with-suggestion):
+
 ```json
 {
   "permissionDecision": "deny",
@@ -116,6 +123,7 @@ Returns `{}` when no rewrite (Cursor requires JSON for all paths).
 ### VS Code Copilot Chat (Rust Binary)
 
 **Input** (stdin, snake_case):
+
 ```json
 {
   "tool_name": "Bash",
@@ -128,6 +136,7 @@ Returns `{}` when no rewrite (Cursor requires JSON for all paths).
 ### Gemini CLI (Rust Binary)
 
 **Input** (stdin):
+
 ```json
 {
   "tool_name": "run_shell_command",
@@ -136,6 +145,7 @@ Returns `{}` when no rewrite (Cursor requires JSON for all paths).
 ```
 
 **Output** (when rewritten):
+
 ```json
 {
   "decision": "allow",
@@ -150,6 +160,7 @@ Returns `{}` when no rewrite (Cursor requires JSON for all paths).
 ### OpenCode (TypeScript Plugin)
 
 Mutates `args.command` in-place via the zx library:
+
 ```typescript
 const result = await $`rtk rewrite ${command}`.quiet().nothrow()
 const rewritten = String(result.stdout).trim()
@@ -230,7 +241,7 @@ New integrations must follow the [Exit Code Contract](#exit-code-contract) and [
 | Tier | Mechanism | Maintenance | Examples |
 |------|-----------|-------------|----------|
 | **Full hook** | Shell script or Rust binary, intercepts commands via agent's hook API | High — must track agent API changes | Claude Code, Cursor, Copilot, Gemini |
-| **Plugin** | TypeScript/JS/Python plugin in agent's plugin system | Medium — agent manages loading | OpenCode, Hermes |
+| **Plugin** | TypeScript/JS/Python plugin in agent's plugin system | Medium — agent manages loading | OpenCode, Hermes, Pi |
 | **Rules file** | Prompt-level instructions the agent reads | Low — no code to break | Cline, Windsurf, Codex |
 
 ### Eligibility

hooks/pi/README.md

@@ -0,0 +1,60 @@
+# Pi Hooks
+
+> Part of [`hooks/`](../README.md) — see also [`src/hooks/`](../../src/hooks/README.md) for installation code
+
+## Design Intent
+
+RTK's Pi extension is a **rewrite-only token optimizer**. It mutates bash commands to their
+`rtk`-prefixed equivalents, saving 60–90% context tokens.
+
+**Permission gating is intentionally out of scope.** RTK does not block, confirm, or audit
+commands — that concern belongs to a dedicated permission extension (e.g. one that gates
+`rm -rf`, `sudo`, etc.). This separation keeps RTK's hook fast, predictable, and composable
+with other Pi extensions.
+
+## Specifics
+
+- TypeScript extension using Pi's `ExtensionAPI` (not a shell hook, no `zx` dependency)
+- Subscribes to `tool_call` event, narrows to `bash` tool via `isToolCallEventType`
+- Calls `rtk rewrite` via `pi.exec`; mutates `event.input.command` in-place if rewrite differs
+- All error paths return `undefined` (pass through); RTK never blocks execution
+- Version guard at load time: checks `rtk >= 0.23.0`; warns and registers no-op if too old or missing
+- Installed to `.pi/extensions/rtk.ts` by `rtk init --agent pi` (project-local) or `~/.pi/agent/extensions/rtk.ts` by `rtk init --agent pi --global`
+
+## Uninstall
+
+```bash
+# Remove project-local install (run from the project root)
+rtk init --uninstall --agent pi
+# → removes .pi/extensions/rtk.ts
+
+# Remove global install
+rtk init --uninstall --agent pi --global
+# → removes ~/.pi/agent/extensions/rtk.ts
+```
+
+Uninstall is idempotent — re-running when nothing is installed is a no-op.
+Only the extension file is managed by install/uninstall.
+
+## Testing
+
+```bash
+# Load the extension directly without installing
+pi -e ./hooks/pi/rtk.ts
+
+# Verify rewrites are active — ask the agent to run a command, then check history
+rtk gain --history   # should show rtk-prefixed commands with savings %
+
+# Test RTK_DISABLED passthrough
+RTK_DISABLED=1 pi -e ./hooks/pi/rtk.ts
+# → commands pass through unchanged; no rewrites in rtk gain --history
+
+# Test version guard — temporarily shadow rtk with a stub that prints "rtk 0.22.0"
+# → extension logs a warning at startup and registers a no-op; pi starts normally
+```
+
+## Design Notes
+
+- All filtering logic lives in `rtk rewrite` (the Rust registry), not in this file
+- Exit codes 0 and 3 both mean "rewrite and allow"; they are handled identically
+- Uses `pi.exec` for subprocess management — consistent with Pi's extension API

hooks/pi/rtk.ts

@@ -0,0 +1,80 @@
+// RTK Pi extension — rewrites bash commands to use rtk for token savings.
+// Requires: rtk >= 0.23.0 in PATH.
+//
+// This is a thin delegating extension: all rewrite logic lives in `rtk rewrite`,
+// which is the single source of truth (src/discover/registry.rs).
+// To add or change rewrite rules, edit the Rust registry — not this file.
+//
+// Exit code contract for `rtk rewrite`:
+//   0 + stdout  Rewrite found → mutate command
+//   1           No RTK equivalent → pass through unchanged
+//   3 + stdout  Rewrite (advisory) → mutate command
+
+import type { ExtensionAPI } from "@earendil-works/pi-coding-agent"
+import { isToolCallEventType } from "@earendil-works/pi-coding-agent"
+
+const REWRITE_TIMEOUT_MS = 2_000
+const MIN_SUPPORTED_RTK_MINOR = 23
+
+// Parse "X.Y.Z" semver, return [major, minor, patch] or null.
+function parseSemver(raw: string): [number, number, number] | null {
+  const m = raw.trim().match(/(\d+)\.(\d+)\.(\d+)/)
+  if (!m) return null
+  return [parseInt(m[1], 10), parseInt(m[2], 10), parseInt(m[3], 10)]
+}
+
+// Calls `rtk rewrite`; returns the rewritten command or null (pass through).
+async function rewriteCommand(
+  pi: ExtensionAPI,
+  cmd: string,
+  signal?: AbortSignal
+): Promise<string | null> {
+  const result = await pi.exec("rtk", ["rewrite", cmd], {
+    timeout: REWRITE_TIMEOUT_MS,
+    signal,
+  })
+  if (result.killed) return null
+  if (result.code !== 0 && result.code !== 3) return null
+  return result.stdout.trim() || null
+}
+
+export default async function (pi: ExtensionAPI) {
+  // Probe rtk version at load time; disables extension if missing or too old.
+  const ver = await pi.exec("rtk", ["--version"], { timeout: REWRITE_TIMEOUT_MS })
+  if (ver.code !== 0) {
+    console.warn("[rtk] rtk binary not found in PATH — extension disabled")
+    return
+  }
+
+  // Warn and bail if rtk predates 0.23.0 (when `rtk rewrite` was introduced).
+  const parsed = parseSemver(ver.stdout.replace(/^rtk\s+/, ""))
+  if (parsed) {
+    const [major, minor] = parsed
+    if (major === 0 && minor < MIN_SUPPORTED_RTK_MINOR) {
+      console.warn(`[rtk] rtk ${ver.stdout.trim()} is too old (need >= 0.23.0) — extension disabled`)
+      return
+    }
+  }
+
+  pi.on("tool_call", async (event, ctx) => {
+    try {
+      if (!isToolCallEventType("bash", event)) return
+
+      const cmd = event.input.command
+      if (typeof cmd !== "string" || cmd.trim() === "") return
+
+      if (cmd.startsWith("rtk ")) return
+      if (process.env.RTK_DISABLED === "1") return
+
+      // Delegate to RTK.
+      const rewritten = await rewriteCommand(pi, cmd, ctx.signal)
+      if (rewritten && rewritten !== cmd) {
+        event.input.command = rewritten
+      }
+    } catch (err) {
+      // Fail open: never block execution on an unexpected error.
+      console.warn("[rtk] unexpected error in tool_call handler; passing through command", err)
+      return
+    }
+  })
+}

src/hooks/README.md

@@ -6,7 +6,7 @@
 
 The **lifecycle management** layer for LLM agent hooks: install, uninstall, verify integrity, audit usage, and manage trust. This component creates and maintains the hook artifacts that live in `hooks/` (root), but does **not** execute rewrite logic itself — that lives in `discover/registry`.
 
-Owns: `rtk init` installation flows (4 agents via `AgentTarget` enum + 3 special modes: Gemini, Codex, OpenCode), SHA-256 integrity verification, hook version checking, audit log analysis, `rtk rewrite` CLI entry point, and TOML filter trust management.
+Owns: `rtk init` installation flows (5 agents via `AgentTarget` enum + 3 special modes: Gemini, Codex, OpenCode), SHA-256 integrity verification, hook version checking, audit log analysis, `rtk rewrite` CLI entry point, and TOML filter trust management.
 
 Does **not** own: the deployed hook scripts themselves (that's `hooks/`), the rewrite pattern registry (that's `discover/`), or command filtering (that's `cmds/`).
 
@@ -22,14 +22,15 @@ LLM agent integration layer that installs, validates, and executes command-rewri
 `rtk init` supports these installation flows:
 
 | Mode | Command | Creates | Patches |
-|------|---------|---------|---------|
+|------|---------|---------|----------|
 | Default (global) | `rtk init -g` | Hook, SHA-256 hash, RTK.md | settings.json, CLAUDE.md |
 | Hook only | `rtk init -g --hook-only` | Hook, SHA-256 hash | settings.json |
 | Claude-MD (legacy) | `rtk init --claude-md` | 134-line RTK block | CLAUDE.md |
 | Windsurf | `rtk init -g --agent windsurf` | `.windsurfrules` | -- |
 | Cline | `rtk init --agent cline` | `.clinerules` | -- |
 | Codex | `rtk init --codex` | RTK.md in `$CODEX_HOME` or `~/.codex` | AGENTS.md |
 | Cursor | `rtk init -g --agent cursor` | Cursor hook | hooks.json |
+| Pi | `rtk init --agent pi` | `.pi/extensions/rtk.ts` | -- |
 | Hermes | `rtk init --agent hermes` | Python plugin in `~/.hermes/plugins/rtk-rewrite/` | `config.yaml` `plugins.enabled` |
 
 

src/hooks/constants.rs

@@ -21,6 +21,13 @@ pub const OPENCODE_PLUGIN_FILE: &str = "rtk.ts";
 pub const CURSOR_DIR: &str = ".cursor";
 pub const CODEX_DIR: &str = ".codex";
 pub const GEMINI_DIR: &str = ".gemini";
+
+pub const PI_DIR: &str = ".pi/agent";
+pub const PI_LOCAL_DIR: &str = ".pi";
+pub const PI_EXTENSIONS_SUBDIR: &str = "extensions";
+pub const PI_PLUGIN_FILE: &str = "rtk.ts";
+pub const PI_CODING_AGENT_DIR_ENV: &str = "PI_CODING_AGENT_DIR";
+
 pub const HERMES_DIR: &str = ".hermes";
 pub const HERMES_PLUGINS_SUBDIR: &str = "plugins";
 pub const HERMES_PLUGIN_NAME: &str = "rtk-rewrite";