Implement before_agent_start hook event

- Add BeforeAgentStartEvent and BeforeAgentStartEventResult types
- Add emitBeforeAgentStart to HookRunner
- Call in AgentSession.prompt() before agent.prompt()
- Hook can return a message to inject into context (persisted + visible)
- Add test hook demonstrating custom message rendering and before_agent_start

.pi/hooks/test-command.ts

@@ -1,24 +1,81 @@
 /**
- * Test hook that registers a /greet command.
- * Usage: /greet [name]
+ * Test hook demonstrating custom commands, message rendering, and before_agent_start.
  */
-import type { HookAPI } from "@mariozechner/pi-coding-agent/hooks";
+import type { HookAPI } from "@mariozechner/pi-coding-agent";
+import { Box, Text } from "@mariozechner/pi-tui";
 
 export default function (pi: HookAPI) {
-	pi.registerCommand("greet", {
-		description: "Send a greeting message to the LLM",
-		handler: async (ctx) => {
-			const name = ctx.args.trim() || "world";
+	// Track whether injection is enabled
+	let injectEnabled = false;
 
-			// Insert a custom message and trigger LLM response
-			pi.sendMessage(
-				{
-					customType: "greeting",
-					content: `Hello, ${name}! Please say something nice about them.`,
-					display: true,
-				},
-				true, // triggerTurn - get LLM to respond
-			);
+	// Register a custom message renderer for our "test-info" type
+	pi.registerMessageRenderer("test-info", (message, options, theme) => {
+		const box = new Box(0, 0, (t) => theme.bg("success", t));
+
+		const label = theme.fg("successText", "[TEST INFO]");
+		box.addChild(new Text(label, 0, 0));
+
+		const content =
+			typeof message.content === "string"
+				? message.content
+				: message.content.map((c) => (c.type === "text" ? c.text : "[image]")).join("");
+
+		box.addChild(new Text(theme.fg("successText", content), 0, 1));
+
+		if (options.expanded && message.details) {
+			box.addChild(new Text(theme.fg("dim", `Details: ${JSON.stringify(message.details)}`), 0, 2));
+		}
+
+		return box;
+	});
+
+	// Register /test-msg command
+	pi.registerCommand("test-msg", {
+		description: "Send a test custom message",
+		handler: async (ctx) => {
+			pi.sendMessage({
+				customType: "test-info",
+				content: "This is a test message with custom rendering!",
+				display: true,
+				details: { timestamp: Date.now(), source: "test-command hook" },
+			});
 		},
 	});
+
+	// Register /test-hidden command
+	pi.registerCommand("test-hidden", {
+		description: "Send a hidden message (display: false)",
+		handler: async (ctx) => {
+			pi.sendMessage({
+				customType: "test-info",
+				content: "This message is in context but not displayed",
+				display: false,
+			});
+			ctx.ui.notify("Sent hidden message (check session file)");
+		},
+	});
+
+	// Register /test-inject command to toggle before_agent_start injection
+	pi.registerCommand("test-inject", {
+		description: "Toggle context injection before agent starts",
+		handler: async (ctx) => {
+			injectEnabled = !injectEnabled;
+			ctx.ui.notify(`Context injection ${injectEnabled ? "enabled" : "disabled"}`);
+		},
+	});
+
+	// Demonstrate before_agent_start: inject context when enabled
+	pi.on("before_agent_start", async (event, ctx) => {
+		if (!injectEnabled) return;
+
+		// Return a message to inject before the user's prompt
+		return {
+			message: {
+				customType: "test-info",
+				content: `[Injected context for prompt: "${event.prompt.slice(0, 50)}..."]`,
+				display: true,
+				details: { injectedAt: Date.now() },
+			},
+		};
+	});
 }