import type { AttachmentFile } from '../entities/AttachmentFile.js';
/**
 * The `attachments` parameter description, shared by the three compose
 * schemas (create_draft, update_draft, send_message) so the wording and the
 * interpolated cap cannot drift between them or from the constant.
 */
export declare const ATTACHMENTS_PARAM_DESCRIPTION: string;
/** MIME type for a filename, by extension; octet-stream when unrecognized. */
export declare function mimeTypeForExtension(filename: string): string;
/**
 * An attachment loaded and encoded for MIME assembly: `data` is standard
 * base64 (the RFC 2045 content-transfer-encoding, not the base64url the API's
 * outer `raw` field uses), folded to 76-character lines because the builder
 * emits the string verbatim and an unfolded multi-megabyte line breaks the
 * RFC 5322 line-length limit.
 */
export type MimeAttachment = {
    filename: string;
    contentType: string;
    data: string;
};
/** Fold a base64 string to 76-character CRLF-separated lines (RFC 2045 §6.8). */
export declare function foldBase64(base64: string): string;
/**
 * Read attachment specs from disk into MIME-ready parts. The combined decoded
 * size is capped at the suite's shared JSON-transfer ceiling; that bounds
 * what this process buffers, not what Gmail accepts (base64 inflates the
 * encoded message ~4/3, so sends near the cap can still be refused by
 * Google; the band past the cap is deferred to issue #103). Each path is
 * stat-checked first: only regular files are read (a FIFO or device file
 * would block or grow unbounded), and an oversize total refuses before the
 * offending file is buffered. Returns undefined when there is nothing to
 * attach.
 */
export declare function loadAttachments(specs: AttachmentFile[] | undefined): Promise<MimeAttachment[] | undefined>;
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