fix: drain OpenAI compat streams for usage

backend/internal/pkg/apicompat/responses_to_chatcompletions.go

@@ -160,7 +160,9 @@ func ResponsesEventToChatChunks(evt *ResponsesStreamEvent, state *ResponsesEvent
 		return resToChatHandleReasoningDelta(evt, state)
 	case "response.reasoning_summary_text.done":
 		return nil
-	case "response.completed", "response.incomplete", "response.failed":
+	// response.done 是 Realtime/WS 与项目透传路径使用的终止别名；
+	// 普通 Responses HTTP SSE 的公开终止事件仍以 response.completed 为主。
+	case "response.completed", "response.done", "response.incomplete", "response.failed":
 		return resToChatHandleCompleted(evt, state)
 	default:
 		return nil