Fix preview platform switching, add stale task cleanup on startup

platform/backend/app/main.py

@@ -48,6 +48,31 @@ Base.metadata.create_all(bind=engine)
 init_db()
 import_initial_data()
 
+# 清理超时任务（运行超过 1 小时的任务视为故障）
+from datetime import datetime, timezone, timedelta
+from .database import SessionLocal
+from .models import ContentTask
+try:
+    cleanup_db = SessionLocal()
+    cutoff = datetime.now(timezone.utc) - timedelta(hours=1)
+    stale = cleanup_db.query(ContentTask).filter(
+        ContentTask.status == "running",
+        ContentTask.started_at.isnot(None),
+        ContentTask.started_at < cutoff
+    ).all()
+    for t in stale:
+        t.status = "failed"
+        t.error_msg = "任务超时（服务重启导致状态丢失）"
+        if t.started_at:
+            t.duration = int((datetime.now(timezone.utc) - t.started_at).total_seconds())
+        logger.warning(f"标记超时任务: {t.task_id}")
+    if stale:
+        cleanup_db.commit()
+        logger.info(f"已清理 {len(stale)} 个超时任务")
+    cleanup_db.close()
+except Exception as e:
+    logger.warning(f"任务清理失败: {e}")
+
 # 注册 API 路由
 app.include_router(topics.router)
 app.include_router(system.router)