fix: preserve original name for warning comparison in transform_string_function_style

The function was replacing spaces with underscores before comparing whether
the name had been modified, so space-only transformations never triggered
the warning. This preserves the original name and compares the final
lowercased result to properly warn on all transformations.

Closes #2951

Signed-off-by: Cocoon-Break <54054995+kuishou68@users.noreply.github.com>

Author: kuishou68

src/agents/util/_transforms.py

@@ -4,18 +4,21 @@
 
 
 def transform_string_function_style(name: str) -> str:
+    # Preserve the original name for comparison and warning message
+    original_name = name
+
     # Replace spaces with underscores
     name = name.replace(" ", "_")
 
     # Replace non-alphanumeric characters with underscores
     transformed_name = re.sub(r"[^a-zA-Z0-9_]", "_", name)
+    final_name = transformed_name.lower()
 
-    if transformed_name != name:
-        final_name = transformed_name.lower()
+    if final_name != original_name:
         logger.warning(
-            f"Tool name {name!r} contains invalid characters for function calling and has been "
+            f"Tool name {original_name!r} contains invalid characters for function calling and has been "
             f"transformed to {final_name!r}. Please use only letters, digits, and underscores "
             "to avoid potential naming conflicts."
         )
 
-    return transformed_name.lower()
+    return final_name