fix(avatar): follow language changes each turn

digital-avatar-app/backend/tests/test_chat_orchestration.py

@@ -11,6 +11,7 @@ from routers.chat import (
     _match_standard_qa,
     _public_avatar_payload,
     _qa_requires_language_adaptation,
+    _qa_requires_per_turn_rendering,
     _require_owned_avatar,
     _resolve_reply,
 )
@@ -86,6 +87,41 @@ class ChatOrchestrationTests(unittest.TestCase):
         self.assertTrue(_qa_requires_language_adaptation("안녕하세요", "你好"))
         self.assertFalse(_qa_requires_language_adaptation("你好", "您好"))
 
+    def test_conversation_qa_is_rendered_for_the_current_turn_language(self):
+        history = [SimpleNamespace(role="user", content="Please answer in English.")]
+        self.assertTrue(_qa_requires_per_turn_rendering("Quelle est votre adresse ?", "Our address is Test Road 1.", history))
+
+        fake_model = Mock(return_value="Notre adresse est Test Road 1.")
+        result = _resolve_reply(
+            None,
+            self.avatar,
+            "Quelle est votre adresse ?",
+            history,
+            qa_pairs=[SimpleNamespace(question="Quelle est votre adresse ?", answer="Our address is Test Road 1.", enabled=True)],
+            search_fn=Mock(),
+            model_client=fake_model,
+        )
+
+        self.assertEqual(result["source"], "qa")
+        self.assertEqual(result["answer"], "Notre adresse est Test Road 1.")
+        messages = fake_model.call_args.kwargs["messages"]
+        self.assertEqual(messages[-1], {"role": "user", "content": "Quelle est votre adresse ?"})
+        self.assertEqual(messages[-2]["role"], "system")
+        self.assertIn("本轮语言覆盖指令", messages[-2]["content"])
+        self.assertIn("不要沿用上一轮语言", messages[-2]["content"])
+
+    def test_latest_user_message_has_an_adjacent_language_override(self):
+        history = [
+            SimpleNamespace(role="user", content="请用中文回答"),
+            SimpleNamespace(role="assistant", content="好的，请问有什么可以帮你？"),
+        ]
+        messages = _build_prompt(self.avatar, history, "What can you help me with?", [])
+
+        self.assertEqual(messages[-1], {"role": "user", "content": "What can you help me with?"})
+        self.assertEqual(messages[-2]["role"], "system")
+        self.assertIn("最新用户消息", messages[-2]["content"])
+        self.assertIn("立即切换到相同语言", messages[-2]["content"])
+
     def test_conversational_paraphrase_matches_standard_qa(self):
         for question in ("请问一下，你们公司在哪里呀？", "请问去你们那边怎么走"):
             with self.subTest(question=question):