```ts
/** The KEY=VALUE pairs of a config file. */
export function parseConfig(text: string): Record<string, string> {
  const config: Record<string, string> = {};
  for (const line of text.split("\n")) {
    const trimmedLine = line.trim();
    if (!trimmedLine || trimmedLine.startsWith("#")) continue;

    const [key, value] = trimmedLine.split("=", 2);
    if (!key) throw new Error(`Invalid config file: empty key on line ${line}`);
    if (value === undefined) throw new Error(`Invalid config file: no '=' on line ${line}`);

    config[key.trim()] = value.trim();
  }
  return config;
}
```