B6/B7: failed终态前端可见 + SSE事件链核实

B6 错误态:
- 后端已加 TaskStatus.FAILED + 异常区分重试中/耗尽(014迁移ALTER status ENUM)
- 前端 TaskStatus 类型加 failed
- RecentTasksBar/history STATUS_LABEL 补 failed 标签
- history 页 HISTORY_STATUSES 纳入 failed(否则失败任务前端找不到)
- FatalErrorBanner + useSse error 不再静默丢弃

B7: 核实 SSE(ticket换JWT) + 事件消费链无缺口,标绿

tsc EXIT=0

frontend/src/stores/generationStore.ts

@@ -28,6 +28,9 @@ interface GenerationState {
   imageCandidates: ImageCandidate[];
   failedBatches: FailedBatch[];
 
+  // 任务级致命错误(SSE error事件,生成彻底失败)。区别于图片批次级 failedBatches。
+  fatalError: { code: number; message: string } | null;
+
   // 飞轮注入（飞轮隐形，只显注入提示，无"训练AI"按钮）
   flywheelInjected: {
     recentPreference: string;
@@ -41,6 +44,7 @@ interface GenerationState {
   setImageProgress: (done: number, total: number) => void;
   addImageCandidate: (candidate: ImageCandidate) => void;
   markBatchFailed: (batch: string, reason: string, retryable: boolean) => void;
+  setFatalError: (code: number, message: string) => void;
   setFlywheelInjected: (data: { recentPreference: string; rejectReasons: string[] }) => void;
   hydrateFromTask: (data: {
     textCandidates: TextCandidate[];
@@ -59,6 +63,7 @@ export const useGenerationStore = create<GenerationState>((set) => ({
   imageTotal: 0,
   imageCandidates: [],
   failedBatches: [],
+  fatalError: null,
   flywheelInjected: null,
 
   setConnectionStatus(s, attempt = 0) {
@@ -95,6 +100,10 @@ export const useGenerationStore = create<GenerationState>((set) => ({
     }));
   },
 
+  setFatalError(code, message) {
+    set({ fatalError: { code, message } });
+  },
+
   setFlywheelInjected(data) {
     set({ flywheelInjected: data });
   },
@@ -116,7 +125,7 @@ export const useGenerationStore = create<GenerationState>((set) => ({
       connectionStatus: 'connecting', reconnectAttempt: 0,
       textDone: 0, textTotal: 0, textCandidates: [],
       imageDone: 0, imageTotal: 0, imageCandidates: [],
-      failedBatches: [], flywheelInjected: null,
+      failedBatches: [], fatalError: null, flywheelInjected: null,
     });
   },
 }));