/**
 * Unified delivery status enum for tracking the lifecycle of message and email deliveries.
 *
 * Replaces both MessageDeliveryStatus (4 states) and EmailDeliveryStatus (7 states)
 * with a single consistent enum used across the entire codebase.
 *
 * @remarks
 * - Pending: Delivery created but not yet announced to the network
 * - Announced: Delivery announced via gossip protocol
 * - Delivered: Recipient node acknowledged successful receipt
 * - Read: Recipient has read the message
 * - Failed: Delivery failed (after retries or post-delivery failure)
 * - Bounced: Recipient node rejected the message
 *
 * @see Requirements 2.1, 2.2, 2.3
 */
export declare enum DeliveryStatus {
    Pending = "pending",
    Announced = "announced",
    Delivered = "delivered",
    Read = "read",
    Failed = "failed",
    Bounced = "bounced"
}
/**
 * Valid state transitions for the DeliveryStatus state machine.
 *
 * Transitions:
 * - Pending → Announced
 * - Announced → Delivered, Failed, Bounced
 * - Delivered → Read, Failed
 * - Read → (terminal)
 * - Failed → (terminal)
 * - Bounced → (terminal)
 *
 * @see Requirements 2.2
 */
export declare const VALID_TRANSITIONS: Record<DeliveryStatus, DeliveryStatus[]>;
/**
 * Validates whether a transition from one DeliveryStatus to another is allowed
 * by the state machine.
 *
 * @param from - The current delivery status
 * @param to - The target delivery status
 * @returns true if the transition is valid, false otherwise
 *
 * @see Requirements 2.2, 2.3
 */
export declare function validateTransition(from: DeliveryStatus, to: DeliveryStatus): boolean;
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