Add overridable hooks for custom chat serving implementations (#25807)

Co-authored-by: Cursor <cursoragent@cursor.com>

python/sglang/srt/managers/tokenizer_manager.py

@@ -216,6 +216,16 @@ class InputFormat(Enum):
 class TokenizerManager(TokenizerControlMixin, TokenizerManagerScoreMixin):
     """TokenizerManager is a process that tokenizes the text."""
 
+    @property
+    def serving_chat_class(self):
+        """Return the serving chat class for OpenAI API.
+
+        Override in subclass to provide custom serving behavior.
+        """
+        from sglang.srt.entrypoints.openai.serving_chat import OpenAIServingChat
+
+        return OpenAIServingChat
+
     def __init__(
         self,
         server_args: ServerArgs,