/**
 * Store a secret in the system keyring.
 * macOS: Keychain via `security` CLI
 * Linux: Secret Service via `secret-tool` CLI
 */
export declare function _setSecret(key: string, value: string, service?: string): Promise<void>;
/**
 * Retrieve a secret from the system keyring.
 * Returns null if the secret doesn't exist.
 */
export declare function _getSecret(key: string, service?: string): Promise<string | null>;
/**
 * Delete a secret from the system keyring.
 * Returns true if the secret was deleted, false if it didn't exist.
 */
export declare function _deleteSecret(key: string, service?: string): Promise<boolean>;
/**
 * Check if the system keyring is available on this platform.
 */
export declare function _isKeyringAvailable(): Promise<boolean>;