fix: anchor reasoning tag detection to line start

Author: Algorithm5838

backend/open_webui/utils/middleware.py

@@ -3312,7 +3312,7 @@ def set_last_text(out, text):
                         if start_tag.startswith('<') and start_tag.endswith('>'):
                             start_tag_pattern = rf'<{re.escape(start_tag[1:-1])}(\s.*?)?>'
 
-                        match = re.search(start_tag_pattern, item_text)
+                        match = re.match(rf'\s*{start_tag_pattern}', item_text)
                         if match:
                             try:
                                 attr_content = match.group(1) if match.group(1) else ''