/**
 * Message Compression Utilities
 *
 * Pure, stateless helpers for compressing and deduplicating LLM message
 * histories. Extracted from `stage-executor.ts` to keep that module focused
 * on orchestration concerns.
 */
import type { LLMMessage } from '../types/llm.types.js';
/**
 * Simple djb2 hash — used to detect duplicate tool results across iterations.
 * Pure arithmetic, no imports needed.
 *
 * Exported for unit testing.
 */
export declare function djb2(s: string): number;
/**
 * Compress a message array in-place by replacing old tool results with a
 * placeholder, keeping the most recent `keepRecent` messages intact.
 * Returns the number of messages replaced.
 *
 * Extracted from `StageExecutor.compressToolResults` for unit testing.
 */
export declare function compressMessageHistory(messages: LLMMessage[], keepRecent?: number): number;
/**
 * Collapse consecutive repeated lines in tool output to `"<line> (×N)"`.
 * Only exact-match consecutive duplicates are collapsed — non-adjacent repeats
 * and blank lines are left untouched to preserve structural context.
 */
export declare function deduplicateLines(text: string): string;
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