export type MediaAttachmentKind = 'image' | 'audio' | 'video' | 'file';
/** Allow private conditional caching, but recheck access before every reuse. */
export declare const MEDIA_CACHE_CONTROL = "private, max-age=0, must-revalidate";
/** Preserve Unicode and the extension while removing unsafe filesystem characters. */
export declare function sanitizeDownloadFileName(value: unknown, fallback?: string): string;
/** RFC 6266: readable ASCII fallback plus the exact UTF-8 filename. */
export declare function buildMediaContentDisposition(input: {
    fileName?: unknown;
    fallbackFileName: string;
    disposition?: 'inline' | 'attachment';
}): string;
/** The processor changes the container to MP4; keep its name consistent everywhere. */
export declare function processedVideoFileName(value: unknown): string;
/** Lifecycle for newly uploaded videos that are normalized server-side. */
export type VideoProcessingStatus = 'processing' | 'ready' | 'failed';
/** Stable, display-safe reasons for a terminal video processing failure. */
export type VideoProcessingErrorCode = 'invalid_video' | 'video_limits_exceeded' | 'video_processing_failed';
export interface MediaAttachment {
    kind: MediaAttachmentKind;
    url: string;
    /**
     * Server-issued identity for a finalized upload. The send path
     * uses this to retain temporary canonical media atomically with the message.
     * Older attachments and forwarded copies may omit it.
     */
    uploadId?: string;
    mimeType?: string;
    fileName?: string;
    sizeBytes?: number;
    width?: number;
    height?: number;
    durationMs?: number;
    /** Server-generated poster for a normalized video. */
    thumbnailUrl?: string;
    /** Missing means a legacy attachment that is immediately playable. */
    processingStatus?: VideoProcessingStatus;
    processingErrorCode?: VideoProcessingErrorCode;
}
export declare function inferMediaAttachmentKind(mimeType: string): MediaAttachmentKind;
export declare function getStoredFileExtension(input: {
    mimeType?: string | null;
    fileName?: string | null;
}): string;
export declare function normalizeStoredAttachments(value: unknown): MediaAttachment[] | null;
export declare function getMessageAttachments(input: {
    attachments?: unknown;
}): MediaAttachment[];
export declare function getPrimaryAttachment(input: {
    attachments?: unknown;
}): MediaAttachment | null;
export declare function describeAttachment(attachment: MediaAttachment | null | undefined): string | null;