Polish Feynman harness and stabilize Pi web runtime

src/pi/launch.ts

@@ -0,0 +1,32 @@
+import { spawn } from "node:child_process";
+import { existsSync } from "node:fs";
+
+import { buildPiArgs, buildPiEnv, type PiRuntimeOptions, resolvePiPaths } from "./runtime.js";
+
+export async function launchPiChat(options: PiRuntimeOptions): Promise<void> {
+	const { piCliPath, promisePolyfillPath } = resolvePiPaths(options.appRoot);
+	if (!existsSync(piCliPath)) {
+		throw new Error(`Pi CLI not found: ${piCliPath}`);
+	}
+	if (!existsSync(promisePolyfillPath)) {
+		throw new Error(`Promise polyfill not found: ${promisePolyfillPath}`);
+	}
+
+	const child = spawn(process.execPath, ["--import", promisePolyfillPath, piCliPath, ...buildPiArgs(options)], {
+		cwd: options.workingDir,
+		stdio: "inherit",
+		env: buildPiEnv(options),
+	});
+
+	await new Promise<void>((resolvePromise, reject) => {
+		child.on("error", reject);
+		child.on("exit", (code, signal) => {
+			if (signal) {
+				process.kill(process.pid, signal);
+				return;
+			}
+			process.exitCode = code ?? 0;
+			resolvePromise();
+		});
+	});
+}