if (typeof inputData.email !== 'string' || !inputData.email.trim()) {
  throw new Error('Missing email');
}
if (typeof inputData.event_id !== 'string' || !inputData.event_id.trim() || Buffer.byteLength(inputData.event_id, 'utf8') > 128) {
  throw new Error('Missing or invalid stable event ID');
}
return { body: JSON.stringify({ email: inputData.email }), event_id: inputData.event_id };