修复：回合失败载荷 stage 未知时不再渲染 undefined

- turn.completed.failure 跨 IPC 没有运行时校验，superErrorFromStringPlusStage 的 stage 缺失或为更新后端新增的取值时，查表得到 undefined 会被拼进用户可见文案
- 查不到标签时回落到通用句"执行失败，请稍后重试"，只有已知阶段才带"请检查项目诊断"

apps/ai-game-creator-shell/src/view/project-development/chat/conversation/directTurnFailure.ts

@@ -176,8 +176,14 @@ export function directTurnFailureNoticeText(failure: TurnFailure): string {
       return `${DIRECT_TURN_SUBJECT} ${directTurnDeadlineText(failure.deadline)}`;
     case 'turnInterrupted':
       return `${DIRECT_TURN_SUBJECT} 本轮执行被中断，请重试`;
-    case 'superErrorFromStringPlusStage':
-      return `${DIRECT_TURN_SUBJECT}：${DIRECT_FAILURE_STAGE_LABELS[failure.stage]}，请检查项目诊断后重试`;
+    case 'superErrorFromStringPlusStage': {
+      // 载荷跨 IPC 没有运行时校验：stage 缺失或是更新后端新增的取值时查不到标签，
+      // 不能把 `undefined` 拼进用户可见文案，回落到通用句。
+      const stageLabel = DIRECT_FAILURE_STAGE_LABELS[failure.stage];
+      return stageLabel
+        ? `${DIRECT_TURN_SUBJECT}：${stageLabel}，请检查项目诊断后重试`
+        : `${DIRECT_TURN_SUBJECT} 执行失败，请稍后重试`;
+    }
     case 'unclassified':
       return `${DIRECT_TURN_SUBJECT} 执行失败，请稍后重试`;
     case 'hostDropped':