/** Infer MIME type from a file extension (case-insensitive).
 *  Returns the fallback if the extension is not recognised. */
export declare function mimeFromExtension(ext: string, fallback?: string): string;
/** True when the MIME type is an image Claude can see via vision.
 *  Tolerates `undefined` so callers can pass an attachment's optional
 *  `mimeType` directly. */
export declare function isImageMime(mimeType: string | undefined): boolean;
/** True when the MIME type is a PDF document Claude can read natively
 *  via `type: "document"` content blocks. Tolerates `undefined`. */
export declare function isPdfMime(mimeType: string | undefined): boolean;
/** True when the attachment can be sent to Claude directly as a
 *  native content block (image or PDF) — no conversion needed.
 *  Tolerates `undefined`. */
export declare function isNativeAttachmentMime(mimeType: string | undefined): boolean;
export declare const isSupportedAttachmentMime: typeof isNativeAttachmentMime;
export interface ParsedDataUrl {
    mimeType: string;
    data: string;
}
/** Parse a `data:<mime>;base64,<data>` string. Returns null if the
 *  format doesn't match. Also handles parameterised data URLs like
 *  `data:image/png;charset=binary;base64,…`. */
export declare function parseDataUrl(dataUrl: string): ParsedDataUrl | null;
/** Build a `data:<mime>;base64,<data>` string from components. */
export declare function buildDataUrl(mimeType: string, base64Data: string): string;