import type { BaseMessage } from '@langchain/core/messages';
/**
 * Deduplicates consecutive identical system messages in the context window.
 *
 * Problem: In long tool-use chains, the same system messages (e.g., post-prune notes,
 * conversation summaries) can accumulate when the context is rebuilt on each iteration.
 * These duplicates waste tokens without adding information.
 *
 * Strategy: Only deduplicate system messages that appear consecutively or are exact
 * duplicates of an earlier system message. The FIRST occurrence is always kept.
 * Non-system messages (human, ai, tool) are never touched.
 *
 * Important constraints:
 * - The first system message (index 0) is ALWAYS preserved (it's the main system prompt)
 * - Only system messages are candidates for deduplication
 * - Messages with content longer than DEDUP_MAX_CONTENT_LENGTH are skipped (too expensive to compare)
 * - Content comparison is by string equality (fast and deterministic)
 *
 * @param messages - The message array to deduplicate (not mutated)
 * @returns A new array with duplicate system messages removed, and the count of removed messages
 */
export declare function deduplicateSystemMessages(messages: BaseMessage[]): {
    messages: BaseMessage[];
    removedCount: number;
};