export interface NegotiationSpeakerParticipants {
    sourceUserId?: unknown;
    candidateUserId?: unknown;
}
export interface NegotiationSpeakerMessage {
    senderId?: unknown;
    parts?: unknown;
}
/**
 * Resolves the participant whose agent owns the next canonical bilateral turn.
 *
 * Participant identities must be nonempty and distinct. Unrelated agent,
 * system, and owner-settlement messages are ignored while finding the latest
 * source/candidate message. An ordinary canonical message passes the floor to
 * the other participant; `ask_user` retains it for the consulting sender's
 * exact successor. A valid conversation with no canonical history starts with
 * the source participant. Invalid participant metadata always fails closed.
 */
export declare function expectedNegotiationSpeaker(participants: NegotiationSpeakerParticipants, messages: readonly NegotiationSpeakerMessage[]): string | null;