Add type assertion for task_request in adaptor.go

relay/channel/task/gemini/adaptor.go

@@ -129,7 +129,10 @@ func (a *TaskAdaptor) BuildRequestBody(c *gin.Context, info *relaycommon.RelayIn
 	if !ok {
 		return nil, fmt.Errorf("request not found in context")
 	}
-	req := v.(relaycommon.TaskSubmitReq)
+	req, ok := v.(relaycommon.TaskSubmitReq)
+	if !ok {
+		return nil, fmt.Errorf("unexpected task_request type")
+	}
 
 	// Create structured video generation request
 	body := GeminiVideoPayload{