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

packages/coding-agent/src/modes/print-mode.ts

@@ -9,28 +9,6 @@
 import type { Attachment } from "@mariozechner/pi-agent-core";
 import type { AssistantMessage } from "@mariozechner/pi-ai";
 import type { AgentSession } from "../core/agent-session.js";
-import type { HookUIContext } from "../core/hooks/index.js";
-
-/**
- * Create a no-op hook UI context for print mode.
- * Hooks can still run but can't prompt the user interactively.
- */
-function createNoOpHookUIContext(): HookUIContext {
-	return {
-		async select() {
-			return null;
-		},
-		async confirm() {
-			return false;
-		},
-		async input() {
-			return null;
-		},
-		notify() {
-			// Silent in print mode
-		},
-	};
-}
 
 /**
  * Run in print (single-shot) mode.
@@ -49,11 +27,21 @@ export async function runPrintMode(
 	initialMessage?: string,
 	initialAttachments?: Attachment[],
 ): Promise<void> {
-	// Initialize hooks with no-op UI context (hooks run but can't prompt)
-	session.setHookUIContext(createNoOpHookUIContext(), (err) => {
-		console.error(`Hook error (${err.hookPath}): ${err.error}`);
-	});
-	await session.initHooks();
+	// Hook runner already has no-op UI context by default (set in main.ts)
+	// Set up hooks for print mode (no UI, ephemeral session)
+	const hookRunner = session.hookRunner;
+	if (hookRunner) {
+		hookRunner.setSessionFile(null); // Print mode is ephemeral
+		hookRunner.onError((err) => {
+			console.error(`Hook error (${err.hookPath}): ${err.error}`);
+		});
+		// No-op send handler for print mode (single-shot, no async messages)
+		hookRunner.setSendHandler(() => {
+			console.error("Warning: pi.send() is not supported in print mode");
+		});
+		// Emit session_start event
+		await hookRunner.emit({ type: "session_start" });
+	}
 
 	if (mode === "json") {
 		// Output all events as JSON