Simplify error message per reviewer feedback

Address @DarkLight1337's review comment: for "required" or named tool_choice,
only --tool-call-parser is needed (--enable-auto-tool-choice is specific to
tool_choice="auto").

Signed-off-by: majiayu000 <[email protected]>

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: majiayu000

tests/entrypoints/openai/test_serving_chat.py

@@ -1426,7 +1426,7 @@ async def test_tool_choice_validation_without_parser():
     assert hasattr(response_required, "body")
     error_body = response_required.body.decode()
     assert "tool_choice" in error_body
-    assert "--enable-auto-tool-choice" in error_body
+    assert "--tool-call-parser" in error_body
 
     # Test named tool_choice without tool_parser
     req_named = ChatCompletionRequest(
@@ -1439,4 +1439,4 @@ async def test_tool_choice_validation_without_parser():
     assert hasattr(response_named, "body")
     error_body = response_named.body.decode()
     assert "tool_choice" in error_body
-    assert "--enable-auto-tool-choice" in error_body
+    assert "--tool-call-parser" in error_body

vllm/entrypoints/openai/serving_chat.py

@@ -227,7 +227,7 @@ async def create_chat_completion(
                     # "required" or named tool requires tool parser
                     return self.create_error_response(
                         f'tool_choice="{request.tool_choice}" requires '
-                        "--enable-auto-tool-choice and --tool-call-parser to be set"
+                        "--tool-call-parser to be set"
                     )
 
             if request.tools is None or (