Preserve standalone model chat templates

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)