feat: enforce knowledge type source hierarchy

ai_knowledge_base_v2/apps/backend/tests/test_knowledge_agent.py

@@ -164,6 +164,34 @@ def test_fixed_information_question_without_catalog_does_not_fall_back_to_genera
         assert result.chunks == []
 
 
+def test_course_type_is_preferred_over_qa_for_course_source_questions():
+    catalog = [
+        {
+            "knowledgeId": 2,
+            "name": "课程常见答疑",
+            "type": "qa",
+            "purpose": "回答课程练习问题",
+            "applicableQuestions": "课程练习",
+            "coreTopics": "静心练习",
+            "publishedAt": "2026-07-17T10:00:00",
+        },
+        {
+            "knowledgeId": 1,
+            "name": "课程原文",
+            "type": "course",
+            "purpose": "说明课程练习方法",
+            "applicableQuestions": "课程练习",
+            "coreTopics": "静心练习",
+            "publishedAt": "2026-07-16T10:00:00",
+        },
+    ]
+
+    need_knowledge, selected_ids, _ = KnowledgeAgentService._decide("课程里的静心练习怎么做？", catalog)
+
+    assert need_knowledge is True
+    assert selected_ids[:2] == [1, 2]
+
+
 def test_fixed_information_is_retrieved_first_and_overrides_other_types():
     with _database() as db:
         _add_published_knowledge(