chore(vendor): import pi 1.3.0

Imported as a linear vendor commit so forge rebases do not replay the upstream root tree.

git-subtree-dir: third_party/pi

git-subtree-split: 71023aec1546d6d677a65669c5665c0927ce0dd0

third_party/pi/packages/agent/examples/mcp-codemode/main.ts

@@ -0,0 +1,50 @@
+/**
+ * An Agent with the tools of an MCP server plus a codemode tool that calls them from JavaScript.
+ *
+ *   ANTHROPIC_API_KEY=... node packages/agent/examples/mcp-codemode/main.ts \
+ *     npx -y @modelcontextprotocol/server-filesystem .
+ *
+ * The arguments are the command that starts a stdio MCP server.
+ */
+
+import { Agent } from "@earendil-works/pi-agent-core";
+import { createModels } from "@earendil-works/pi-ai";
+import { anthropicProvider } from "@earendil-works/pi-ai/providers/anthropic";
+import { McpClient, StdioTransport } from "@earendil-works/pi-mcp";
+import { createCodemodeTool, createMcpTools, createNestedToolRunner } from "./tools.ts";
+
+const [command, ...args] = process.argv.slice(2);
+if (!command) {
+	console.error("Usage: main.ts <mcp server command> [args...]");
+	process.exit(1);
+}
+
+const models = createModels();
+models.setProvider(anthropicProvider());
+const model = models.getModel("anthropic", "claude-sonnet-4-6");
+if (!model) throw new Error("Model not found");
+
+const client = new McpClient({ name: "pi-agent-example", version: "1.0.0" });
+await client.connect(new StdioTransport({ command, args }));
+
+try {
+	const agent = new Agent({
+		initialState: { systemPrompt: "You are a helpful assistant.", model },
+		streamFn: models.streamSimple.bind(models),
+	});
+	const mcpTools = await createMcpTools(client, "mcp");
+	// The model can call the MCP tools directly or batch them in one codemode script.
+	agent.state.tools = [...mcpTools, createCodemodeTool(mcpTools, createNestedToolRunner(agent))];
+
+	agent.subscribe((event) => {
+		if (event.type === "message_update" && event.assistantMessageEvent.type === "text_delta") {
+			process.stdout.write(event.assistantMessageEvent.delta);
+		} else if (event.type === "tool_execution_start") {
+			console.log(`\n[${event.toolName}]`);
+		}
+	});
+	await agent.prompt("Use codemode to list what the MCP tools can do, then summarize it in two sentences.");
+	console.log();
+} finally {
+	await client.close();
+}