export declare class EnvAssignmentError extends Error {
}
/** Change only exact assignments to one valid key; reject ambiguous layouts before any write. */
export declare function prepareEnvAssignment(assignment: string, existing: string): {
    key: string;
    content: string;
};
/** Use one regular-file descriptor; never follow a link or create a file for invalid input. */
export declare function setEnvAssignment(path: string, assignment: string): string;