/**
 * HTTP Utilities for PEAC Protocol
 *
 * Cache safety and header management helpers for adapters and middleware.
 */
/**
 * Headers that affect response behavior and MUST be included in Vary
 * when enforcement decisions depend on them.
 */
export declare const VARY_HEADERS: readonly ["PEAC-Purpose", "PEAC-Receipt"];
/**
 * Apply Vary header for purpose-aware caching.
 *
 * MUST be called when response behavior varies based on PEAC-Purpose header.
 * Prevents cache poisoning when different purposes get different responses.
 *
 * @example
 * ```ts
 * // In Cloudflare Worker
 * const response = new Response(body, { headers });
 * applyPurposeVary(response.headers);
 *
 * // In Express/Node
 * applyPurposeVary(res);
 * ```
 */
export declare function applyPurposeVary(headers: Headers | {
    setHeader: (name: string, value: string) => void;
} | {
    set: (name: string, value: string) => void;
}): void;
/**
 * Get all PEAC-related headers that should be included in Vary
 * for complete cache safety.
 *
 * @returns Comma-separated list of headers for Vary
 */
export declare function getPeacVaryHeaders(): string;
/**
 * Check if a response needs Vary header based on purpose enforcement.
 *
 * @param purposeEnforced - Whether purpose was enforced for this response
 * @returns true if Vary: PEAC-Purpose should be set
 */
export declare function needsPurposeVary(purposeEnforced: boolean): boolean;
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