import type { BaselineData, BaselineEntry, BaselineComparison } from "../types.js";
/**
 * Save a baseline snapshot for a URL.
 * Appends to the history file (never overwrites existing entries).
 */
export declare function saveBaseline(url: string, results: BaselineData, outputDir?: string): Promise<BaselineEntry>;
/**
 * Load the most recent baseline for a given URL.
 * Returns null if no baseline exists.
 */
export declare function loadBaseline(url: string, outputDir?: string): Promise<BaselineEntry | null>;
/**
 * Load all baseline entries from the history file.
 */
export declare function loadAllBaselines(outputDir?: string): Promise<readonly BaselineEntry[]>;
/**
 * Compare two baseline snapshots and categorize each metric
 * as improved, regressed, or unchanged.
 */
export declare function compareToBaseline(current: BaselineData, previous: BaselineData): BaselineComparison;
/**
 * Format a baseline comparison as readable markdown.
 * Now includes letter grade transitions for score-based metrics.
 */
export declare function formatBaselineComparison(comparison: BaselineComparison): string;
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