feat(exam): 出题批卷 API 增强 — 格式统一、校验、跨调用去重

- grader: 多策略 JSON 提取 + 3 次重试 + prompt 优化，修复 LLM 输出不稳定问题
- grader: question_content → content 统一字段名，与出题接口一致
- api: 新增入参校验（题型枚举、difficulty、总题数上限 20、grade question_type）
- api/generator/manager: 新增 exclude_stems 参数，支持跨调用去重

exam_pkg/api.py

@@ -61,6 +61,22 @@ def validate_difficulty(difficulty) -> str:
         return "difficulty 必须为 1-5 的整数"
     return None
 
+
+MAX_EXCLUDE_STEMS = 100
+
+def validate_exclude_stems(exclude_stems) -> str:
+    """校验 exclude_stems 参数（可选）"""
+    if exclude_stems is None:
+        return None
+    if not isinstance(exclude_stems, list):
+        return "exclude_stems 必须为字符串数组"
+    if len(exclude_stems) > MAX_EXCLUDE_STEMS:
+        return f"exclude_stems 数量不能超过 {MAX_EXCLUDE_STEMS}，当前 {len(exclude_stems)}"
+    for i, stem in enumerate(exclude_stems):
+        if not isinstance(stem, str) or not stem.strip():
+            return f"exclude_stems 第 {i+1} 项必须为非空字符串"
+    return None
+
 # 创建蓝图
 exam_bp = Blueprint('exam', __name__)
 
@@ -86,6 +102,7 @@ def api_generate_questions():
             "subjective": 1
         },
         "difficulty": 3,
+        "exclude_stems": ["已有题目的题干1", "已有题目的题干2"],  // 可选，排除已有题目避免重复
         "options": {
             "include_explanation": true,
             "max_source_chunks": 50
@@ -135,6 +152,20 @@ def api_generate_questions():
         if diff_error:
             return error_response("INVALID_PARAMS", BAD_REQUEST, diff_error, http_status=400)
 
+        # 校验总题数上限
+        MAX_TOTAL_QUESTIONS = 20
+        total_requested = sum(question_types.values())
+        if total_requested > MAX_TOTAL_QUESTIONS:
+            return error_response("INVALID_PARAMS", BAD_REQUEST,
+                f"总题数不能超过 {MAX_TOTAL_QUESTIONS} 道，当前请求 {total_requested} 道",
+                http_status=400)
+
+        # 校验排除题干列表（可选）
+        exclude_stems = data.get('exclude_stems')
+        stems_error = validate_exclude_stems(exclude_stems)
+        if stems_error:
+            return error_response("INVALID_PARAMS", BAD_REQUEST, stems_error, http_status=400)
+
         # 获取当前用户
         user = get_current_user()
         if not user:
@@ -156,7 +187,8 @@ def api_generate_questions():
             question_types=question_types,
             difficulty=data.get('difficulty', 3),
             options=data.get('options', {}),
-            request_id=data.get('request_id')
+            request_id=data.get('request_id'),
+            exclude_stems=data.get('exclude_stems')
         )
 
         return success_response(data=result, status_code=EXAM_SUCCESS, message="出题成功")
@@ -199,6 +231,12 @@ def api_generate_smart():
         if diff_error:
             return error_response("INVALID_PARAMS", BAD_REQUEST, diff_error, http_status=400)
 
+        # 校验排除题干列表（可选）
+        exclude_stems = data.get('exclude_stems')
+        stems_error = validate_exclude_stems(exclude_stems)
+        if stems_error:
+            return error_response("INVALID_PARAMS", BAD_REQUEST, stems_error, http_status=400)
+
         # 获取当前用户
         user = get_current_user()
         if not user:
@@ -231,7 +269,8 @@ def api_generate_smart():
             question_types=question_types,
             difficulty=data.get('difficulty', 3),
             options=data.get('options', {}),
-            request_id=data.get('request_id')
+            request_id=data.get('request_id'),
+            exclude_stems=data.get('exclude_stems')
         )
 
         # 3. 在返回结果中添加 AI 分析信息
@@ -258,21 +297,21 @@ def api_grade_answers():
             {
                 "question_id": "uuid",
                 "question_type": "single_choice",
-                "question_content": {"answer": "B"},
+                "content": {"answer": "B"},
                 "student_answer": "A",
                 "max_score": 2
             },
             {
                 "question_id": "uuid",
                 "question_type": "fill_blank",
-                "question_content": {"answer": [["答案1"], ["答案2"]]},
+                "content": {"answer": [["答案1", "同义词"], ["答案2"]]},
                 "student_answer": ["学生答案1", "学生答案2"],
                 "max_score": 4
             },
             {
                 "question_id": "uuid",
                 "question_type": "subjective",
-                "question_content": {
+                "content": {
                     "stem": "简述...",
                     "data": {"scoring_points": [...]},
                     "answer": "参考范文..."
@@ -283,6 +322,12 @@ def api_grade_answers():
         ]
     }
 
+    说明：
+    - content 字段与出题接口返回的 content 结构一致，后端可直接透传
+    - 客观题：content 只需包含 answer
+    - 填空题：content.answer 格式为 [["答案1", "同义词"], ...] 每空一个列表
+    - 主观题：content 需包含 stem + answer + data.scoring_points
+
     返回:
     {
         "success": true,
@@ -312,6 +357,14 @@ def api_grade_answers():
         if not answers:
             return error_response("MISSING_PARAMS", BAD_REQUEST, "缺少答案数据", http_status=400)
 
+        # 校验每道题的 question_type
+        for i, ans in enumerate(answers):
+            q_type = ans.get('question_type')
+            if q_type not in VALID_QUESTION_TYPES:
+                return error_response("INVALID_PARAMS", BAD_REQUEST,
+                    f"第 {i+1} 题的 question_type 无效: {q_type}，合法值: {', '.join(sorted(VALID_QUESTION_TYPES))}",
+                    http_status=400)
+
         # 调用新版批题接口
         result = grade_answers(
             answers=answers,