fix: 恢复腾讯云账单同步并完善成本预测

- 接入腾讯云单日账单、全局限频和指数退避

- 修正月末费用预测并增加账期提示和费用归因

- 补充腾讯云限频及账单归因回归测试

backend/cloud/tencent.go

@@ -5,17 +5,39 @@ import (
 	"crypto/sha256"
 	"encoding/hex"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
 	"sort"
 	"strings"
+	"sync"
 	"time"
 )
 
 // TencentProvider 通过腾讯云 TC3-HMAC-SHA256 API 同步 CVM 资源。 // Logan.Li
 type TencentProvider struct{ accessKey, secretKey string }
 
+const (
+	tencentRequestInterval = 260 * time.Millisecond
+	tencentMaxAttempts     = 4
+)
+
+var tencentLimiter = struct {
+	sync.Mutex
+	next time.Time
+}{}
+
+// tencentAPIError 保留腾讯云错误码，便于对限频错误做退避重试。 // Logan.Li
+type tencentAPIError struct {
+	Code    string
+	Message string
+}
+
+func (e *tencentAPIError) Error() string {
+	return fmt.Sprintf("腾讯云 API 错误 %s: %s", e.Code, e.Message)
+}
+
 // tencentInstancesResponse 描述腾讯云 CVM 实例分页响应。 // Logan.Li
 type tencentInstancesResponse struct {
 	Response struct {
@@ -58,6 +80,44 @@ func (p *TencentProvider) callInRegion(region, action string, payload interface{
 
 // callService 使用 TC3-HMAC-SHA256 调用腾讯云服务 API。 // Logan.Li
 func (p *TencentProvider) callService(service, host, version, action, region string, payload interface{}) ([]byte, error) {
+	var lastErr error
+	for attempt := 0; attempt < tencentMaxAttempts; attempt++ {
+		waitTencentRequestSlot()
+		data, err := p.callServiceOnce(service, host, version, action, region, payload)
+		if err == nil {
+			return data, nil
+		}
+		lastErr = err
+		delay, retry := tencentRetryDelay(err, attempt)
+		if !retry {
+			return nil, err
+		}
+		time.Sleep(delay)
+	}
+	return nil, lastErr
+}
+
+// waitTencentRequestSlot 将进程内所有腾讯云请求统一限速在每秒 4 次以内。 // Logan.Li
+func waitTencentRequestSlot() {
+	tencentLimiter.Lock()
+	defer tencentLimiter.Unlock()
+	if delay := time.Until(tencentLimiter.next); delay > 0 {
+		time.Sleep(delay)
+	}
+	tencentLimiter.next = time.Now().Add(tencentRequestInterval)
+}
+
+// tencentRetryDelay 对 RequestLimitExceeded 使用指数退避，其他错误立即返回。 // Logan.Li
+func tencentRetryDelay(err error, attempt int) (time.Duration, bool) {
+	var apiErr *tencentAPIError
+	if !errors.As(err, &apiErr) || !strings.HasPrefix(apiErr.Code, "RequestLimitExceeded") || attempt >= tencentMaxAttempts-1 {
+		return 0, false
+	}
+	return (500 * time.Millisecond) * time.Duration(1<<attempt), true
+}
+
+// callServiceOnce 执行一次腾讯云 TC3-HMAC-SHA256 签名请求。 // Logan.Li
+func (p *TencentProvider) callServiceOnce(service, host, version, action, region string, payload interface{}) ([]byte, error) {
 	body, err := json.Marshal(payload)
 	if err != nil {
 		return nil, fmt.Errorf("编码腾讯云请求失败: %w", err)
@@ -95,6 +155,9 @@ func (p *TencentProvider) callService(service, host, version, action, region str
 		return nil, fmt.Errorf("读取腾讯云响应失败: %w", err)
 	}
 	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		if resp.StatusCode == http.StatusTooManyRequests {
+			return nil, &tencentAPIError{Code: "RequestLimitExceeded.HTTP429", Message: string(data)}
+		}
 		return nil, fmt.Errorf("腾讯云 API 返回 HTTP %d: %s", resp.StatusCode, string(data))
 	}
 	var envelope struct {
@@ -106,7 +169,7 @@ func (p *TencentProvider) callService(service, host, version, action, region str
 		} `json:"Response"`
 	}
 	if json.Unmarshal(data, &envelope) == nil && envelope.Response.Error != nil {
-		return nil, fmt.Errorf("腾讯云 API 错误 %s: %s", envelope.Response.Error.Code, envelope.Response.Error.Message)
+		return nil, &tencentAPIError{Code: envelope.Response.Error.Code, Message: envelope.Response.Error.Message}
 	}
 	return data, nil
 }