/**
 * Image payload handling for screenshots.
 *
 * Screenshots travel as base64 and end up inlined in an MCP tool result. On a
 * high-DPI display a full-viewport capture of a visually dense page runs to
 * tens of megabytes, which is far past what any client wants in its context and
 * past the 10 MB read buffer newer MCP stdio transports enforce. So the format
 * is negotiable, and the size is measured rather than assumed.
 */
export declare const SUPPORTED_IMAGE_MIME_TYPES: Set<string>;
export interface ParsedImage {
    mimeType: string;
    base64: string;
}
/**
 * Reads a data URL into its mime type and payload. A bare base64 string is
 * treated as PNG, which is what the extension has always produced, so a client
 * that omits the prefix does not silently write a corrupt file.
 */
export declare function parseImageDataUrl(value: string): ParsedImage | null;
export declare function extensionForMimeType(mimeType: string): string;
/** Forces a filename's extension to match the bytes actually being written. */
export declare function withExtension(name: string, extension: string): string;
/** Decoded size of a base64 payload, without decoding it. */
export declare function approximateBytes(base64: string): number;