fix: align agent no-hit handling

ai_knowledge_base_v2/apps/backend/tests/test_agent_runtime_config.py

@@ -16,6 +16,7 @@ from app.schemas.admin import AgentDebugRequest, AgentRuntimeConfigSaveRequest
 from app.services.agent_debug_service import AgentDebugService
 from app.services.model_stream_service import (
     AsyncStreamingModelResponse,
+    ModelStreamService,
     _openai_stream_payload,
     _stream_configured_model_async,
 )
@@ -194,12 +195,71 @@ def test_debug_preview_passes_conversation_history_and_replaces_saved_prompt():
 
     kwargs = build_result.await_args.kwargs
     assert [item.content for item in kwargs["history"]] == ["最开始的问题", "第一次回答"]
+    assert kwargs["preview_knowledge_ids"] is None
+    assert kwargs["version_overrides"] is None
     assert kwargs["prompt_override"] == "调试主提示词"
     assert kwargs["response_depth"] == 35
     assert result.messages == rag_result.messages
     assert result.prompt == "调试提示词渲染结果"
 
 
+def test_agent_debug_empty_knowledge_selection_uses_formal_open_catalog():
+    payload = AgentDebugRequest(
+        promptContent="调试主提示词",
+        modelId=1,
+        knowledgeIds=[],
+        knowledgeVersions={},
+        question="测试问题",
+    )
+    rag_result = RagResult(
+        question="测试问题",
+        knowledge_scopes=[],
+        chunks=[],
+        prompt="测试",
+        allow_general_knowledge=True,
+    )
+
+    with _database() as db:
+        build_result = AsyncMock(return_value=rag_result)
+        with patch("app.services.agent_debug_service.KnowledgeAgentService.build_result", build_result):
+            asyncio.run(AgentDebugService.build_result(db, payload))
+
+    kwargs = build_result.await_args.kwargs
+    assert kwargs["preview_knowledge_ids"] is None
+    assert kwargs["version_overrides"] is None
+
+
+def test_user_stream_no_hit_still_calls_model_for_cautious_answer():
+    async def configured_chunks(_model, _rag_result):
+        yield "我暂时没有可靠课程依据，但可以先帮你整理需要确认的点。"
+
+    async def collect():
+        with _database() as db:
+            model = _model()
+            db.add_all([
+                model,
+                SystemConfig(config_key="mock_model_enabled", config_value="false"),
+            ])
+            db.commit()
+            rag_result = RagResult(
+                question="课程里的特殊练习怎么做？",
+                knowledge_scopes=[],
+                chunks=[],
+                prompt="本轮没有可靠的正式知识章节。",
+                allow_general_knowledge=False,
+            )
+            with patch(
+                "app.services.model_stream_service._stream_configured_model_async",
+                configured_chunks,
+            ):
+                response = ModelStreamService.stream_async(db, rag_result)
+                return [chunk async for chunk in response.chunks]
+
+    chunks = asyncio.run(collect())
+
+    assert chunks == ["我暂时没有可靠课程依据，但可以先帮你整理需要确认的点。"]
+
+
 def test_prompt_includes_response_depth_instruction():
     with _database() as db:
         db.add(SystemConfig(config_key="agent_response_depth", config_value="20"))