fix(exam_pkg): v2补题去重与final已有题干交叉去重

补题阶段仅和exclude_stems去重，未检查final中已有题干，
可能补出重复题目。修复：收集final题干+exclude_stems合并传入
_deduplicate_questions，多题型补题时逐轮累积排除列表。

exam_pkg/generator.py

@@ -1300,12 +1300,21 @@ def generate_questions_structured_v2(
 
     if shortage_types:
         logger.info(f"  [v2] 补题: 缺少题型 {dict(shortage_types)}")
+        # 收集 final 中已有题干，补题时一并排除
+        existing_stems = [q.get('content', {}).get('stem', '') for q in final if q.get('content', {}).get('stem')]
+        combined_exclude = list(exclude_stems or []) + existing_stems
+
         for q_type, shortage in shortage_types.items():
             logger.info(f"    补充 {q_type} {shortage} 道...")
             extra = generator._makeup_questions(chunks, q_type, shortage, difficulty, document_name)
-            # 补题也需去重
-            extra_deduped = _deduplicate_questions(extra, exclude_stems=exclude_stems)
+            # 补题需与已有题目 + 跨调用排除列表一起去重
+            extra_deduped = _deduplicate_questions(extra, exclude_stems=combined_exclude)
             final.extend(extra_deduped[:shortage])
+            # 将新补的题干也加入排除列表，防止后续题型补出重复
+            for q in extra_deduped:
+                stem = q.get('content', {}).get('stem', '')
+                if stem:
+                    combined_exclude.append(stem)
 
         # 补题后重新统计
         type_counts = defaultdict(int)