[Frontend] early return chat format resolution when specified (#19735)

vllm/entrypoints/chat_utils.py

@@ -448,6 +448,9 @@ def resolve_chat_template_content_format(
     model_config: ModelConfig,
     trust_remote_code: Optional[bool] = None,
 ) -> _ChatTemplateContentFormat:
+    if given_format != "auto":
+        return given_format
+
     detected_format = _resolve_chat_template_content_format(
         chat_template,
         tools,
@@ -461,7 +464,7 @@ def resolve_chat_template_content_format(
         detected_format=detected_format,
     )
 
-    return detected_format if given_format == "auto" else given_format
+    return detected_format