File or media attachment associated with a message.

Supports image, file, and audio types. The data field contains the content as a base64 string or data URI. Attachments are sent with user messages via TransportMessage and stored in AgentMessage.

interface Attachment {
    type: 'image' | 'file' | 'audio';
    name: string;
    data: string;
    mimeType: string;
}