<?php
declare(strict_types=1);

namespace Oscar\MailEngine\MimeContent;

final class InMemoryMimeContent implements MimeContentInterface
{
    // ... existing properties ...

    public function getAttachmentStream(string $messageId, int $idx, string $accountId): mixed
    {
        $stream = fopen('php://temp', 'r+');
        fwrite($stream, 'mock attachment data');
        rewind($stream);
        return $stream;
    }

    // ... other existing methods ...
}