/**
 * Envelope metadata – security metadata value object (timestamp, nonce, version).
 *
 * @remarks
 * Immutable; validates timestamp (positive, not in the future) and protocol version.
 */
import type { CPEMetadata, ProtocolVersion, Timestamp } from '../types.js';
import type { Nonce as NonceVO } from './Nonce.js';
/** Current protocol version for envelope metadata */
export declare const CURRENT_PROTOCOL_VERSION: ProtocolVersion;
/**
 * Creates envelope metadata (frozen).
 *
 * @param timestamp - Unix timestamp in ms
 * @param nonce - Nonce value object
 * @param protocolVersion - Protocol version (default: CURRENT_PROTOCOL_VERSION)
 * @param previousSignatures - Optional previous layer signatures (csl, isl)
 */
export declare function createMetadata(timestamp: Timestamp, nonce: NonceVO, protocolVersion?: ProtocolVersion, previousSignatures?: {
    csl?: string;
    isl?: string;
}): CPEMetadata;
/**
 * Validates metadata shape and values.
 */
export declare function isValidMetadata(metadata: CPEMetadata): boolean;
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