develop: 补齐 agent 上报 HTTP 常量并修复测试编译

internal/agent/reporter.go

@@ -13,6 +13,13 @@ import (
 	"git.opencomputing.cn/yumoqing/host-metrics-collector/pkg/collectorpb"
 )
 
+// Agent 上报使用的 HTTP 头与内容类型，与 gateway 包及测试保持一致。
+const (
+	headerAgentToken    = "X-Agent-Token"
+	headerHostID        = "X-Host-Id"
+	contentTypeProtobuf = "application/x-protobuf"
+)
+
 // Reporter 负责通过 HTTP/protobuf 向 Collector Gateway（4318）上报数据。
 type Reporter struct {
 	client       *http.Client
@@ -110,9 +117,9 @@ func (r *Reporter) post(ctx context.Context, path string, req proto.Message, out
 	if err != nil {
 		return fmt.Errorf("new request: %w", err)
 	}
-	httpReq.Header.Set("Content-Type", "application/x-protobuf")
-	httpReq.Header.Set("X-Agent-Token", r.agentToken)
-	httpReq.Header.Set("X-Host-Id", r.hostID)
+	httpReq.Header.Set("Content-Type", contentTypeProtobuf)
+	httpReq.Header.Set(headerAgentToken, r.agentToken)
+	httpReq.Header.Set(headerHostID, r.hostID)
 
 	resp, err := r.client.Do(httpReq)
 	if err != nil {