/**
* Thread-key derivation from RFC 5322 `Message-ID`, `In-Reply-To`,
* and `References` headers. Given a parsed email we return a stable
* identifier that groups messages in the same conversation.
*
* @module
*/
import type { ParsedEmail } from "../parse/index.mjs";
export interface ThreadKeyInput {
	messageId?: string;
	inReplyTo?: string;
	references?: ReadonlyArray<string>;
}
/** Pick the canonical root Message-ID for a parsed email. */
export declare function threadKey(input: ThreadKeyInput | ParsedEmail): string;
/** Build a deterministic adjacency list `{ root -> [member-ids] }` from
*  a batch of parsed messages. Useful for UI grouping. */
export declare function buildThreads(messages: ReadonlyArray<ThreadKeyInput>): Map<string, string[]>;