Add hooks system with pi.send() for external message injection

- Hook discovery from ~/.pi/agent/hooks/, .pi/hooks/, --hook flag - Events: session_start, session_switch, agent_start/end, turn_start/end, tool_call, tool_result, branch - tool_call can block execution, tool_result can modify results - pi.send(text, attachments?) to inject messages from external sources - UI primitives: ctx.ui.select/confirm/input/notify - Context: ctx.exec(), ctx.cwd, ctx.sessionFile, ctx.hasUI - Docs shipped with npm package and binary builds - System prompt references docs folder
2026-04-15 20:03:05 +00:00 · 2025-12-10 00:50:30 +01:00 · 2025-12-10 00:50:30 +01:00 · 7c553acd1e
commit 7c553acd1e
parent 942d8d3c95
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--- a/packages/coding-agent/docs/hooks.md
+++ b/packages/coding-agent/docs/hooks.md
@ -0,0 +1,609 @@
+# Hooks
+
+Hooks are TypeScript modules that extend the coding agent's behavior by subscribing to lifecycle events. They can intercept tool calls, prompt the user for input, modify results, and more.
+
+## Hook Locations
+
+Hooks are automatically discovered from two locations:
+
+1. **Global hooks**: `~/.pi/agent/hooks/*.ts`
+2. **Project hooks**: `<cwd>/.pi/hooks/*.ts`
+
+All `.ts` files in these directories are loaded automatically. Project hooks let you define project-specific behavior (similar to `.pi/AGENTS.md`).
+
+### Additional Configuration
+
+You can also add explicit hook paths in `~/.pi/agent/settings.json`:
+
+```json
+{
+  "hooks": [
+    "/path/to/custom/hook.ts"
+  ],
+  "hookTimeout": 30000
+}
+```
+
+- `hooks`: Additional hook file paths (supports `~` expansion)
+- `hookTimeout`: Timeout in milliseconds for non-interactive hook operations (default: 30000)
+
+## Writing a Hook
+
+A hook is a TypeScript file that exports a default function. The function receives a `HookAPI` object used to subscribe to events.
+
+```typescript
+import type { HookAPI } from "@mariozechner/pi-coding-agent";
+
+export default function (pi: HookAPI) {
+  pi.on("session_start", async (event, ctx) => {
+    ctx.ui.notify(`Session: ${ctx.sessionFile ?? "ephemeral"}`, "info");
+  });
+}
+```
+
+### Setup
+
+Create a hooks directory and initialize it:
+
+```bash
+# Global hooks
+mkdir -p ~/.pi/agent/hooks
+cd ~/.pi/agent/hooks
+npm init -y
+npm install @mariozechner/pi-coding-agent
+
+# Or project-local hooks
+mkdir -p .pi/hooks
+cd .pi/hooks
+npm init -y
+npm install @mariozechner/pi-coding-agent
+```
+
+Hooks are loaded using [jiti](https://github.com/unjs/jiti), so TypeScript works without compilation.
+
+## Events
+
+### Lifecycle
+
+```
+pi starts
+  │
+  ├─► session_start
+  │
+  ▼
+user sends prompt ─────────────────────────────────────────┐
+  │                                                        │
+  ├─► agent_start                                          │
+  │                                                        │
+  │   ┌─── turn (repeats while LLM calls tools) ───┐       │
+  │   │                                            │       │
+  │   ├─► turn_start                               │       │
+  │   │                                            │       │
+  │   │   LLM responds, may call tools:            │       │
+  │   │     ├─► tool_call (can block)              │       │
+  │   │     │   tool executes                      │       │
+  │   │     └─► tool_result (can modify)           │       │
+  │   │                                            │       │
+  │   └─► turn_end                                 │       │
+  │                                                        │
+  └─► agent_end                                            │
+                                                           │
+user sends another prompt ◄────────────────────────────────┘
+
+user branches or switches session
+  │
+  └─► session_switch
+```
+
+A **turn** is one LLM response plus any tool calls. Complex tasks loop through multiple turns until the LLM responds without calling tools.
+
+### session_start
+
+Fired once when pi starts.
+
+```typescript
+pi.on("session_start", async (event, ctx) => {
+  // ctx.sessionFile: string | null
+  // ctx.hasUI: boolean
+});
+```
+
+### session_switch
+
+Fired when session changes (`/branch` or session switch).
+
+```typescript
+pi.on("session_switch", async (event, ctx) => {
+  // event.newSessionFile: string
+  // event.previousSessionFile: string
+  // event.reason: "branch" | "switch"
+});
+```
+
+### agent_start / agent_end
+
+Fired once per user prompt.
+
+```typescript
+pi.on("agent_start", async (event, ctx) => {});
+
+pi.on("agent_end", async (event, ctx) => {
+  // event.messages: AppMessage[] - new messages from this prompt
+});
+```
+
+### turn_start / turn_end
+
+Fired for each turn within an agent loop.
+
+```typescript
+pi.on("turn_start", async (event, ctx) => {
+  // event.turnIndex: number
+  // event.timestamp: number
+});
+
+pi.on("turn_end", async (event, ctx) => {
+  // event.turnIndex: number
+  // event.message: AppMessage - assistant's response
+  // event.toolResults: AppMessage[]
+});
+```
+
+### tool_call
+
+Fired before tool executes. **Can block.**
+
+```typescript
+pi.on("tool_call", async (event, ctx) => {
+  // event.toolName: "bash" | "read" | "write" | "edit" | "ls" | "find" | "grep"
+  // event.toolCallId: string
+  // event.input: Record<string, unknown>
+  return { block: true, reason: "..." }; // or undefined to allow
+});
+```
+
+Tool inputs:
+- `bash`: `{ command, timeout? }`
+- `read`: `{ path, offset?, limit? }`
+- `write`: `{ path, content }`
+- `edit`: `{ path, oldText, newText }`
+- `ls`: `{ path?, limit? }`
+- `find`: `{ pattern, path?, limit? }`
+- `grep`: `{ pattern, path?, glob?, ignoreCase?, literal?, context?, limit? }`
+
+### tool_result
+
+Fired after tool executes. **Can modify result.**
+
+```typescript
+pi.on("tool_result", async (event, ctx) => {
+  // event.toolName, event.toolCallId, event.input
+  // event.result: string
+  // event.isError: boolean
+  return { result: "modified" }; // or undefined to keep original
+});
+```
+
+### branch
+
+Fired when user branches via `/branch`.
+
+```typescript
+pi.on("branch", async (event, ctx) => {
+  // event.targetTurnIndex: number
+  // event.entries: SessionEntry[]
+  return { skipConversationRestore: true }; // or undefined
+});
+```
+
+## Context API
+
+Every event handler receives a context object with these methods:
+
+### ctx.ui.select(title, options)
+
+Show a selector dialog. Returns the selected option or `null` if cancelled.
+
+```typescript
+const choice = await ctx.ui.select("Pick one:", ["Option A", "Option B"]);
+if (choice === "Option A") {
+  // ...
+}
+```
+
+### ctx.ui.confirm(title, message)
+
+Show a confirmation dialog. Returns `true` if confirmed, `false` otherwise.
+
+```typescript
+const confirmed = await ctx.ui.confirm("Delete file?", "This cannot be undone.");
+if (confirmed) {
+  // ...
+}
+```
+
+### ctx.ui.input(title, placeholder?)
+
+Show a text input dialog. Returns the input string or `null` if cancelled.
+
+```typescript
+const name = await ctx.ui.input("Enter name:", "default value");
+```
+
+### ctx.ui.notify(message, type?)
+
+Show a notification. Type can be `"info"`, `"warning"`, or `"error"`.
+
+```typescript
+ctx.ui.notify("Operation complete", "info");
+ctx.ui.notify("Something went wrong", "error");
+```
+
+### ctx.exec(command, args)
+
+Execute a command and get the result.
+
+```typescript
+const result = await ctx.exec("git", ["status"]);
+// result.stdout: string
+// result.stderr: string
+// result.code: number
+```
+
+### ctx.cwd
+
+The current working directory.
+
+```typescript
+console.log(`Working in: ${ctx.cwd}`);
+```
+
+### ctx.sessionFile
+
+Path to the session file, or `null` if running with `--no-session`.
+
+```typescript
+if (ctx.sessionFile) {
+  console.log(`Session: ${ctx.sessionFile}`);
+}
+```
+
+### ctx.hasUI
+
+Whether interactive UI is available. `false` in print and RPC modes.
+
+```typescript
+if (ctx.hasUI) {
+  const choice = await ctx.ui.select("Pick:", ["A", "B"]);
+} else {
+  // Fall back to default behavior
+}
+```
+
+## Sending Messages
+
+Hooks can inject messages into the agent session using `pi.send()`. This is useful for:
+
+- Waking up the agent when an external event occurs (file change, CI result, etc.)
+- Async debugging (inject debug output from other processes)
+- Triggering agent actions from external systems
+
+```typescript
+pi.send(text: string, attachments?: Attachment[]): void
+```
+
+If the agent is currently streaming, the message is queued. Otherwise, a new agent loop starts immediately.
+
+### Example: File Watcher
+
+```typescript
+import * as fs from "node:fs";
+import type { HookAPI } from "@mariozechner/pi-coding-agent";
+
+export default function (pi: HookAPI) {
+  pi.on("session_start", async (event, ctx) => {
+    // Watch a trigger file
+    const triggerFile = "/tmp/agent-trigger.txt";
+    
+    fs.watch(triggerFile, () => {
+      try {
+        const content = fs.readFileSync(triggerFile, "utf-8").trim();
+        if (content) {
+          pi.send(`External trigger: ${content}`);
+          fs.writeFileSync(triggerFile, ""); // Clear after reading
+        }
+      } catch {
+        // File might not exist yet
+      }
+    });
+    
+    ctx.ui.notify("Watching /tmp/agent-trigger.txt", "info");
+  });
+}
+```
+
+To trigger: `echo "Run the tests" > /tmp/agent-trigger.txt`
+
+### Example: HTTP Webhook
+
+```typescript
+import * as http from "node:http";
+import type { HookAPI } from "@mariozechner/pi-coding-agent";
+
+export default function (pi: HookAPI) {
+  pi.on("session_start", async (event, ctx) => {
+    const server = http.createServer((req, res) => {
+      let body = "";
+      req.on("data", chunk => body += chunk);
+      req.on("end", () => {
+        pi.send(body || "Webhook triggered");
+        res.writeHead(200);
+        res.end("OK");
+      });
+    });
+    
+    server.listen(3333, () => {
+      ctx.ui.notify("Webhook listening on http://localhost:3333", "info");
+    });
+  });
+}
+```
+
+To trigger: `curl -X POST http://localhost:3333 -d "CI build failed"`
+
+**Note:** `pi.send()` is not supported in print mode (single-shot execution).
+
+## Examples
+
+### Shitty Permission Gate
+
+```typescript
+import type { HookAPI } from "@mariozechner/pi-coding-agent";
+
+export default function (pi: HookAPI) {
+  const dangerousPatterns = [
+    /\brm\s+(-rf?|--recursive)/i,
+    /\bsudo\b/i,
+    /\b(chmod|chown)\b.*777/i,
+  ];
+
+  pi.on("tool_call", async (event, ctx) => {
+    if (event.toolName !== "bash") return undefined;
+
+    const command = event.input.command as string;
+    const isDangerous = dangerousPatterns.some((p) => p.test(command));
+
+    if (isDangerous) {
+      const choice = await ctx.ui.select(
+        `⚠️ Dangerous command:\n\n  ${command}\n\nAllow?`,
+        ["Yes", "No"]
+      );
+
+      if (choice !== "Yes") {
+        return { block: true, reason: "Blocked by user" };
+      }
+    }
+
+    return undefined;
+  });
+}
+```
+
+### Git Checkpointing
+
+Stash code state at each turn so `/branch` can restore it.
+
+```typescript
+import type { HookAPI } from "@mariozechner/pi-coding-agent";
+
+export default function (pi: HookAPI) {
+  const checkpoints = new Map<number, string>();
+
+  pi.on("turn_start", async (event, ctx) => {
+    // Create a git stash entry before LLM makes changes
+    const { stdout } = await ctx.exec("git", ["stash", "create"]);
+    const ref = stdout.trim();
+    if (ref) {
+      checkpoints.set(event.turnIndex, ref);
+    }
+  });
+
+  pi.on("branch", async (event, ctx) => {
+    const ref = checkpoints.get(event.targetTurnIndex);
+    if (!ref) return undefined;
+
+    const choice = await ctx.ui.select("Restore code state?", [
+      "Yes, restore code to that point",
+      "No, keep current code",
+    ]);
+
+    if (choice?.startsWith("Yes")) {
+      await ctx.exec("git", ["stash", "apply", ref]);
+      ctx.ui.notify("Code restored to checkpoint", "info");
+    }
+
+    return undefined;
+  });
+
+  pi.on("agent_end", async () => {
+    checkpoints.clear();
+  });
+}
+```
+
+### Block Writes to Certain Paths
+
+```typescript
+import type { HookAPI } from "@mariozechner/pi-coding-agent";
+
+export default function (pi: HookAPI) {
+  const protectedPaths = [".env", ".git/", "node_modules/"];
+
+  pi.on("tool_call", async (event, ctx) => {
+    if (event.toolName !== "write" && event.toolName !== "edit") {
+      return undefined;
+    }
+
+    const path = event.input.path as string;
+    const isProtected = protectedPaths.some((p) => path.includes(p));
+
+    if (isProtected) {
+      ctx.ui.notify(`Blocked write to protected path: ${path}`, "warning");
+      return { block: true, reason: `Path "${path}" is protected` };
+    }
+
+    return undefined;
+  });
+}
+```
+
+## Mode Behavior
+
+Hooks behave differently depending on the run mode:
+
+| Mode | UI Methods | Notes |
+|------|-----------|-------|
+| Interactive | Full TUI dialogs | User can interact normally |
+| RPC | JSON protocol | Host application handles UI |
+| Print (`-p`) | No-op (returns null/false) | Hooks run but can't prompt |
+
+In print mode, `select()` returns `null`, `confirm()` returns `false`, and `input()` returns `null`. Design hooks to handle these cases gracefully.
+
+## Error Handling
+
+- If a hook throws an error, it's logged and the agent continues
+- If a `tool_call` hook errors or times out, the tool is **blocked** (fail-safe)
+- Hook errors are displayed in the UI with the hook path and error message
+
+## Debugging
+
+To debug a hook:
+
+1. Open VS Code in your hooks directory
+2. Open a **JavaScript Debug Terminal** (Ctrl+Shift+P → "JavaScript Debug Terminal")
+3. Set breakpoints in your hook file
+4. Run `pi --hook ./my-hook.ts` in the debug terminal
+
+The `--hook` flag loads a hook directly without needing to modify `settings.json` or place files in the standard hook directories.
+
+---
+
+# Internals
+
+## Discovery and Loading
+
+Hooks are discovered and loaded at startup in `main.ts`:
+
+```
+main.ts
+  -> discoverAndLoadHooks(configuredPaths, cwd)  [loader.ts]
+     -> discoverHooksInDir(~/.pi/agent/hooks/)   # global hooks
+     -> discoverHooksInDir(cwd/.pi/hooks/)       # project hooks
+     -> merge with configuredPaths (deduplicated)
+     -> for each path:
+        -> jiti.import(path)                     # TypeScript support via jiti
+        -> hookFactory(hookAPI)                  # calls pi.on() to register handlers
+        -> returns LoadedHook { path, handlers: Map<eventType, handlers[]> }
+```
+
+## Tool Wrapping
+
+Tools are wrapped with hook callbacks before the agent is created:
+
+```
+main.ts
+  -> wrapToolsWithHooks(tools, hookRunner)  [tool-wrapper.ts]
+     -> returns new tools with wrapped execute() functions
+```
+
+The wrapped `execute()` function:
+
+1. Checks `hookRunner.hasHandlers("tool_call")`
+2. If yes, calls `hookRunner.emitToolCall(event)` (no timeout)
+3. If result has `block: true`, throws an error
+4. Otherwise, calls the original `tool.execute()`
+5. Checks `hookRunner.hasHandlers("tool_result")`
+6. If yes, calls `hookRunner.emit(event)` (with timeout)
+7. Returns (possibly modified) result
+
+## HookRunner
+
+The `HookRunner` class manages hook execution:
+
+```typescript
+class HookRunner {
+  constructor(hooks: LoadedHook[], cwd: string, timeout?: number)
+  
+  setUIContext(ctx: HookUIContext, hasUI: boolean): void
+  setSessionFile(path: string | null): void
+  onError(listener): () => void
+  hasHandlers(eventType: string): boolean
+  emit(event: HookEvent): Promise<Result>
+  emitToolCall(event: ToolCallEvent): Promise<ToolCallEventResult | undefined>
+}
+```
+
+Key behaviors:
+- `emit()` has a timeout (default 30s) for safety
+- `emitToolCall()` has **no timeout** (user prompts can take any amount of time)
+- Errors in `emit()` are caught and reported via `onError()`
+- Errors in `emitToolCall()` propagate (causing tool to be blocked)
+
+## Event Flow
+
+```
+Mode initialization:
+  -> hookRunner.setUIContext(ctx, hasUI)
+  -> hookRunner.setSessionFile(path)
+  -> hookRunner.emit({ type: "session_start" })
+
+User sends prompt:
+  -> AgentSession.prompt()
+     -> hookRunner.emit({ type: "agent_start" })
+     -> hookRunner.emit({ type: "turn_start", turnIndex })
+     -> agent loop:
+        -> LLM generates tool calls
+        -> For each tool call:
+           -> wrappedTool.execute()
+              -> hookRunner.emitToolCall({ type: "tool_call", ... })
+              -> [if not blocked] originalTool.execute()
+              -> hookRunner.emit({ type: "tool_result", ... })
+        -> LLM generates response
+     -> hookRunner.emit({ type: "turn_end", ... })
+     -> [repeat if more tool calls]
+  -> hookRunner.emit({ type: "agent_end", messages })
+
+Branch or session switch:
+  -> AgentSession.branch() or AgentSession.switchSession()
+     -> hookRunner.emit({ type: "session_switch", ... })
+```
+
+## UI Context by Mode
+
+Each mode provides its own `HookUIContext` implementation:
+
+**Interactive Mode** (`interactive-mode.ts`):
+- `select()` -> `HookSelectorComponent` (TUI list selector)
+- `confirm()` -> `HookSelectorComponent` with Yes/No options
+- `input()` -> `HookInputComponent` (TUI text input)
+- `notify()` -> Adds text to chat container
+
+**RPC Mode** (`rpc-mode.ts`):
+- All methods send JSON requests via stdout
+- Waits for JSON responses via stdin
+- Host application renders UI and sends responses
+
+**Print Mode** (`print-mode.ts`):
+- All methods return null/false immediately
+- `notify()` is a no-op
+
+## File Structure
+
+```
+packages/coding-agent/src/core/hooks/
+├── index.ts          # Public exports
+├── types.ts          # Event types, HookAPI, contexts
+├── loader.ts         # jiti-based hook loading
+├── runner.ts         # HookRunner class
+└── tool-wrapper.ts   # Tool wrapping for interception
+```