Preserve standalone model chat templates

README.md

@@ -16,7 +16,8 @@
 - 对明确写成 `TokenizersBackend` 且带 `tokenizer.json` 的仓库，改用
   `PreTrainedTokenizerFast`。
 - 对 `model_type=qwen2`、`eos_token=<|im_end|>` 且缺少聊天模板的模型，补充
-  简单的 Qwen ChatML 模板，避免 `/v1/chat/completions` 返回 400。
+  简单的 Qwen ChatML 模板，避免 `/v1/chat/completions` 返回 400；已有独立
+  `chat_template.jinja` 或 `chat_template.json` 的模型不补写。
 
 启动时在 `/tmp` 建立新模型视图，只重写 `tokenizer_config.json`。权重、模型代码和
 其他文件以符号链接指回只读 `/model`；源模型不变。没有命中上述问题时直接调用原始

engine_compat.py

@@ -81,7 +81,14 @@ def repair_tokenizer_config(
         patched["tokenizer_class"] = "PreTrainedTokenizerFast"
         repairs.append("TokenizersBackend -> PreTrainedTokenizerFast")
 
-    if not patched.get("chat_template"):
+    # Transformers can load a standalone template with higher precedence than
+    # tokenizer_config.json. Do not synthesize one when the repository already
+    # supplies a template in that format.
+    has_standalone_template = any(
+        (model_dir / name).is_file()
+        for name in ("chat_template.jinja", "chat_template.json")
+    )
+    if not patched.get("chat_template") and not has_standalone_template:
         config_path = model_dir / "config.json"
         if config_path.is_file():
             model_config = _json_object(config_path)

tests/test_engine_compat.py

@@ -53,6 +53,14 @@ class EngineCompatTests(unittest.TestCase):
             self.assertIsNone(prepare_model(source, work_root=root))
             self.assertEqual([p.name for p in root.iterdir()], ["model"])
 
+    def test_standalone_chat_template_is_preserved(self):
+        for filename in ("chat_template.jinja", "chat_template.json"):
+            with self.subTest(filename=filename), tempfile.TemporaryDirectory() as directory:
+                root = Path(directory)
+                source = self._model(root, {"eos_token": "<|im_end|>"})
+                (source / filename).write_text("{{ messages }}", encoding="utf-8")
+                self.assertIsNone(prepare_model(source, work_root=root))
+
     def test_known_tokenizer_class_is_replaced_only_with_tokenizer_json(self):
         with tempfile.TemporaryDirectory() as directory:
             root = Path(directory)