/**
 * Header Utilities
 *
 * 提供头部操作的工具函数：
 * - 查找、赋值、删除头部字段
 * - 头部 key 标准化
 */
export declare class HeaderUtils {
    static findHeaderValue(headers: Record<string, string>, target: string): string | undefined;
    static normalizeHeaderKey(value: string): string;
    static assignHeader(headers: Record<string, string>, target: string, value: string): void;
    static deleteHeader(headers: Record<string, string>, target: string): void;
    static setHeaderIfMissing(headers: Record<string, string>, target: string, value: string): void;
    static copyHeaderValue(target: Record<string, string>, source: Record<string, string>, from: string, to: string): void;
}