fix: revalidate review context and serialize index retry

backend/wisegrade/services.py

@@ -137,8 +137,11 @@ def enqueue_index_task(db, task_id: int):
 
 
 def retry_index_task(db, source_id: int):
-    source = found(db, IndexTask, source_id)
+    source = db.scalar(select(IndexTask).where(IndexTask.id == source_id).with_for_update())
+    if not source:
+        raise HTTPException(404, "索引任务不存在")
     if source.status != "failed":
+        db.rollback()
         raise HTTPException(409, "仅失败的索引任务可重试")
     existing = db.scalar(select(IndexTask).where(IndexTask.id > source.id,
         IndexTask.course_version_id == source.course_version_id,
@@ -146,6 +149,7 @@ def retry_index_task(db, source_id: int):
         IndexTask.kind == source.kind, IndexTask.status.in_(["queued", "running", "completed"]))
         .order_by(IndexTask.id.desc()))
     if existing:
+        db.commit()
         return existing
     retry = IndexTask(course_version_id=source.course_version_id, submission_file_id=source.submission_file_id,
                       kind=source.kind, status="queued")