import { BaseMessage, HumanMessage } from '@langchain/core/messages';
/**
 * Adds a system message to the chat history.
 *
 * @param {BaseMessage[]} messages - The message array to extend.
 * @param {string} message - The system message content.
 */
export declare function addSystemMessage(messages: BaseMessage[], message: string): BaseMessage[];
/**
 * Returns the last human message from the chat history.
 *
 * @param {BaseMessage[]} messages - The message array to search.
 * @returns {HumanMessage | undefined} - The last human message or undefined if not found.
 */
export declare function lastHumanMessage(messages: BaseMessage[]): HumanMessage | undefined;
/**
 * Replaces the last human message in the chat history with a new one.
 *
 * @param {BaseMessage[]} messages - The message array to modify.
 * @param {HumanMessage} newMessage - The new human message to replace the last one.
 * @returns {BaseMessage[]} - The updated message array.
 */
export declare function replaceLastHumanMessage(messages: BaseMessage[], newMessage: HumanMessage): BaseMessage[];
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