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/mcp/test/helpers.ts

@@ -0,0 +1,40 @@
+import { createServer, type IncomingMessage, type Server, type ServerResponse } from "node:http";
+
+export type HttpHandler = (request: IncomingMessage, response: ServerResponse, origin: string) => Promise<void>;
+
+const servers: Server[] = [];
+
+export async function readBody(request: IncomingMessage): Promise<string> {
+	const chunks: Buffer[] = [];
+	for await (const chunk of request) chunks.push(Buffer.from(chunk));
+	return Buffer.concat(chunks).toString("utf8");
+}
+
+/** Starts a loopback HTTP server and returns its origin. Call `closeServers` from `afterEach`. */
+export async function listen(handler: HttpHandler): Promise<string> {
+	let origin = "";
+	const server = createServer((request, response) => {
+		void handler(request, response, origin).catch((error) => {
+			response.statusCode = 500;
+			response.end(String(error));
+		});
+	});
+	await new Promise<void>((resolve) => server.listen(0, "127.0.0.1", resolve));
+	const address = server.address();
+	if (!address || typeof address === "string") throw new Error("HTTP test server did not bind to TCP");
+	origin = `http://127.0.0.1:${address.port}`;
+	servers.push(server);
+	return origin;
+}
+
+export async function closeServers(): Promise<void> {
+	await Promise.all(
+		servers.splice(0).map(
+			(server) =>
+				new Promise<void>((resolve, reject) => {
+					server.closeAllConnections();
+					server.close((error) => (error ? reject(error) : resolve()));
+				}),
+		),
+	);
+}