/**
 * A2A headers encoding/decoding for email body
 *
 * Supports embedding A2A metadata in HTML comments (legacy) or
 * CSS hidden span (new format) when real email headers are not available.
 */
import type { EmailLogger } from "../utils/logger.js";
/**
 * A2A headers extracted from body
 */
export interface A2ABodyHeaders {
    /** Agent identifier */
    agent: string | null;
    /** Turn number */
    turn: number;
}
/**
 * Check if body content is HTML format
 * @param body - Email body content
 * @returns true if body contains HTML tags
 */
export declare function isHtmlBody(body: string): boolean;
/**
 * Extract A2A headers from CSS hidden span (new format)
 * Format: <span style="display:none...">{"__oc":1,"agent":"...","turn":N}</span>
 */
export declare function extractA2AFromHiddenSpan(body: string): A2ABodyHeaders;
/**
 * Inject A2A metadata as CSS hidden span appended to HTML body (new format)
 * Used by WS transport where real email headers are not available.
 */
export declare function injectA2AAsHiddenSpan(body: string, agent: string, turn: number, log?: EmailLogger): string;
/**
 * Extract A2A headers from HTML body comments (legacy format)
 * @param body - Email body (HTML or plain text)
 * @returns Extracted A2A headers
 */
export declare function extractA2AFromHtmlBody(body: string): A2ABodyHeaders;
/**
 * Remove existing A2A comments from body
 * @param body - HTML body content
 * @returns Body with A2A comments removed
 */
export declare function stripExistingA2AComments(body: string): string;
/**
 * Strip all A2A metadata from HTML before Markdown conversion.
 * Removes hidden span (new format) and HTML comments (legacy format).
 * Use this before passing HTML to turndown so A2A metadata is not visible to AI.
 * @param html - Raw HTML content (does NOT mutate the original)
 * @returns HTML with all A2A metadata removed
 */
export declare function stripA2AFromHtml(html: string): string;
/**
 * Inject A2A headers into HTML body as comments
 * @param body - Original email body
 * @param agent - Agent identifier
 * @param turn - Turn number
 * @param log - Optional logger
 * @returns Body with A2A comments injected
 */
export declare function injectA2AIntoHtmlBody(body: string, agent: string, turn: number, log?: EmailLogger): string;