fix(acceptance): 物化验收任务的最终媒体

仅对已认证 Acceptance Run 强制下载并持久化 URL 型结果，确保集群外压测端能验证最终视频；普通生产任务继续遵循现有文件存储策略。压测器仅对 Gateway 自有地址做双入口重写，避免向第三方媒体域名泄露验收凭据。\n\n同时修复本地集群重复使用同一快照文件时的幂等复制失败。验证：Go 全量测试、go vet、gofmt、bash -n、ShellCheck 和 git diff --check 通过。

apps/api/cmd/acceptance-load/main.go

@@ -760,7 +760,7 @@ func pollVideoTask(ctx context.Context, client *http.Client, opts options, taskI
 					if mediaURL == "" {
 						return fmt.Errorf("video task %s succeeded without a media URL", taskID)
 					}
-					return validateVideoAsset(ctx, client, mediaURL)
+					return validateVideoAsset(ctx, client, opts, mediaURL, index)
 				case "failed", "cancelled", "canceled":
 					return fmt.Errorf("video task %s finished with status %s", taskID, status)
 				}
@@ -780,15 +780,34 @@ func pollVideoTask(ctx context.Context, client *http.Client, opts options, taskI
 func findMediaURL(value any) string {
 	switch typed := value.(type) {
 	case map[string]any:
-		for key, item := range typed {
+		preferredKeys := []string{"video_url", "url", "data", "content", "output", "result", "upload"}
+		visited := make(map[string]struct{}, len(typed))
+		for _, key := range preferredKeys {
+			item, ok := typed[key]
+			if !ok {
+				continue
+			}
+			visited[key] = struct{}{}
 			normalized := strings.ToLower(strings.TrimSpace(key))
-			if (normalized == "url" || normalized == "video_url") && strings.HasPrefix(strings.TrimSpace(fmt.Sprint(item)), "http") {
+			if (normalized == "url" || normalized == "video_url") && acceptanceMediaURL(strings.TrimSpace(fmt.Sprint(item))) {
 				return strings.TrimSpace(fmt.Sprint(item))
 			}
 			if mediaURL := findMediaURL(item); mediaURL != "" {
 				return mediaURL
 			}
 		}
+		keys := make([]string, 0, len(typed)-len(visited))
+		for key := range typed {
+			if _, ok := visited[key]; !ok {
+				keys = append(keys, key)
+			}
+		}
+		sort.Strings(keys)
+		for _, key := range keys {
+			if mediaURL := findMediaURL(typed[key]); mediaURL != "" {
+				return mediaURL
+			}
+		}
 	case []any:
 		for _, item := range typed {
 			if mediaURL := findMediaURL(item); mediaURL != "" {
@@ -799,11 +818,22 @@ func findMediaURL(value any) string {
 	return ""
 }
 
-func validateVideoAsset(ctx context.Context, client *http.Client, mediaURL string) error {
-	request, err := http.NewRequestWithContext(ctx, http.MethodGet, mediaURL, nil)
+func acceptanceMediaURL(value string) bool {
+	return strings.HasPrefix(value, "/") || strings.HasPrefix(value, "http://") || strings.HasPrefix(value, "https://")
+}
+
+func validateVideoAsset(ctx context.Context, client *http.Client, opts options, mediaURL string, index int) error {
+	requestURL, gatewayRequest, err := acceptanceMediaRequestURL(opts, mediaURL, index)
+	if err != nil {
+		return fmt.Errorf("resolve final video: %w", err)
+	}
+	request, err := http.NewRequestWithContext(ctx, http.MethodGet, requestURL, nil)
 	if err != nil {
 		return err
 	}
+	if gatewayRequest {
+		opts.setHeaders(request, index, false)
+	}
 	response, err := client.Do(request)
 	if err != nil {
 		return fmt.Errorf("download final video: %w", err)
@@ -824,6 +854,46 @@ func validateVideoAsset(ctx context.Context, client *http.Client, mediaURL strin
 	return nil
 }
 
+func acceptanceMediaRequestURL(opts options, mediaURL string, index int) (string, bool, error) {
+	mediaURL = strings.TrimSpace(mediaURL)
+	if mediaURL == "" {
+		return "", false, errors.New("empty media URL")
+	}
+	if strings.HasPrefix(mediaURL, "/") {
+		if len(opts.gateways) == 0 {
+			return "", false, errors.New("no gateway URL configured")
+		}
+		base, err := url.Parse(opts.gateways[index%len(opts.gateways)])
+		if err != nil {
+			return "", false, err
+		}
+		reference, err := url.Parse(mediaURL)
+		if err != nil {
+			return "", false, err
+		}
+		return base.ResolveReference(reference).String(), true, nil
+	}
+	parsed, err := url.Parse(mediaURL)
+	if err != nil {
+		return "", false, err
+	}
+	if opts.gatewayTLSName == "" || !strings.EqualFold(parsed.Hostname(), opts.gatewayTLSName) {
+		return parsed.String(), false, nil
+	}
+	if len(opts.gateways) == 0 {
+		return "", false, errors.New("no gateway URL configured")
+	}
+	base, err := url.Parse(opts.gateways[index%len(opts.gateways)])
+	if err != nil {
+		return "", false, err
+	}
+	base.Path = parsed.Path
+	base.RawPath = parsed.RawPath
+	base.RawQuery = parsed.RawQuery
+	base.Fragment = parsed.Fragment
+	return base.String(), true, nil
+}
+
 func (o options) setHeaders(request *http.Request, requestIndex int, realUpstream bool) {
 	if o.gatewayTLSName != "" {
 		request.Host = o.gatewayTLSName