Function assertPortsFree

scripts/dev-safe.mjs:256–275

(portConfigs, host = "127.0.0.1")

 * @param {string} [host]
 */
export async function assertPortsFree(portConfigs, host = "127.0.0.1") {
  const results = await Promise.all(
    portConfigs.map(async ({ name, port }) => ({
      name,
      port,
      free: await tryPort(port, host),
    })),
  );
  const busy = results.filter(({ free }) => !free);
  if (busy.length === 0) return;

  const lines = busy
    .map(({ name, port }) => `   • ${name}: port ${port}`)
    .join("\n");
  throw new Error(
    `Cannot start: the following ports are already in use:\n\n${lines}\n\n` +
      `Another agent-canvas instance may already be running.\n` +
      `Stop it first, or override the port via environment variables (e.g. PORT=<other>).`,
  );
}

/**
 * Find multiple free ports at once, each preferring its specified default.