// ==================== 纯请求函数 ====================
/**
 * 请求 K 线数据
 * @param {string} endpoint API 端点 URL
 * @param {number} timeoutMs 超时毫秒数，默认 45000
 * @returns {Promise<object>} 解析后的 JSON 对象
 * @throws {Error} 网络错误、HTTP 错误、超时错误、解析错误
 */
async function requestKlines(endpoint, timeoutMs = 45000) {
    const controller = new AbortController();
    const timeoutId = setTimeout(() => controller.abort(), timeoutMs);
    
    try {
        const response = await fetch(endpoint, {
            method: 'GET',
            headers: { 'Accept': 'application/json' },
            signal: controller.signal
        });
        clearTimeout(timeoutId);
        
        if (!response.ok) {
            throw new Error(`HTTP ${response.status}`);
        }
        
        const json = await response.json();
        if (!json || Object.keys(json).length === 0) {
            throw new Error('后端返回空对象');
        }
        return json;
    } catch (err) {
        clearTimeout(timeoutId);
        if (err.name === 'AbortError') {
            throw new Error('请求超时');
        }
        throw err;
    }
}