/** Initialize (or re-initialize) the encryption key. Call once at startup. */
export declare function initEncryption(secret: string): void;
/**
 * Encrypt a plaintext string.
 * Returns format: `enc:<iv>:<authTag>:<ciphertext>` (all base64).
 */
export declare function encrypt(plaintext: string): string;
/**
 * Decrypt a value produced by encrypt().
 * If the value doesn't have the `enc:` prefix, returns it as-is (backward compat for plaintext).
 */
export declare function decrypt(value: string): string;
/** Check whether a value is already encrypted */
export declare function isEncrypted(value: string): boolean;
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