export type SniffedImageMediaType = "image/jpeg" | "image/png" | "image/gif" | "image/webp";
export type SniffedMediaType = SniffedImageMediaType | "application/pdf";
export declare function normalizeImageMediaType(value: string | undefined): SniffedImageMediaType | null;
export declare function sniffAttachmentMediaType(base64: string | undefined): SniffedMediaType | null;
export type AttachmentBytesVerdict<M extends SniffedMediaType> = {
    kind: "ok";
    mediaType: M;
} | {
    kind: "undecodable";
    declared: string;
} | {
    kind: "truncated";
    mediaType: SniffedMediaType;
} | {
    kind: "wrong-kind";
    declared: string;
    actual: SniffedMediaType;
};
export type AttachmentBytesRejection = Exclude<AttachmentBytesVerdict<SniffedMediaType>, {
    kind: "ok";
}>;
export declare function reconcileImageBytes(input: {
    base64: string | undefined;
    declared: string;
}): AttachmentBytesVerdict<SniffedImageMediaType>;
export declare function reconcilePdfBytes(input: {
    base64: string | undefined;
    declared: string;
}): AttachmentBytesVerdict<"application/pdf">;
export declare function describeAttachmentBytesVerdict(verdict: AttachmentBytesRejection): string;