diff -r 75abdd7f2568 roundup/cgi/templating.py
--- a/roundup/cgi/templating.py	Thu Jul 30 17:16:32 2026 -0400
+++ b/roundup/cgi/templating.py	Mon Aug 03 02:57:21 2026 +0000
@@ -3741,18 +3741,38 @@
 
     """
 
-    def __getattr__(self, name):
-        """Try the tracker's templating_utils."""
-        if not hasattr(self.client.instance, 'templating_utils'):
-            # backwards-compatibility
-            raise AttributeError(name)
-        if name not in self.client.instance.templating_utils:
-            raise AttributeError(name)
-        return self.client.instance.templating_utils[name]
+    def __getattribute__(self, name):
+        client = super().__getattribute__('client')
+
+        if (hasattr(client.instance, 'templating_utils') and
+            (name in client.instance.templating_utils) ):
+            return client.instance.templating_utils[name]
+
+        # a lot of client lookups are done, we already have it
+        # just return it.
+        if name == "client": return client
+
+        return super().__getattribute__(name)
 
     def keywords_expressions(self, request):
         return render_keywords_expression_editor(request)
 
+    @staticmethod
+    def localReplace(message):
+        """Default no-op for localReplace.
+
+           Override with real definition in extensions.
+
+           This allows templates to ship with localReplace(....)
+           and have an:
+
+               instance.registerUtil('localReplace', local_replace)
+
+           define localReplace with the same call signature (i.e. no self)
+           in the extension definition.
+        """
+        return message
+
     def html_calendar(self, request):
         """Generate a HTML calendar.
 
diff -r 75abdd7f2568 roundup/instance.py
--- a/roundup/instance.py	Thu Jul 30 17:16:32 2026 -0400
+++ b/roundup/instance.py	Mon Aug 03 02:57:21 2026 +0000
@@ -262,6 +262,16 @@
            instead.
 
         """
+        # prevent overriding of internal TemplatingUtil methods/vars.
+        if name.startswith('_'):
+            import inspect
+            caller = inspect.stack()[1]
+            raise ValueError(
+                "Can't define template utility named '%(name)s' at:\n"
+                "   %(filename)s:%(lineno)d\n"
+                "   Utility names must not start with '_'.\n"
+                % {**caller._asdict(), "name": name})
+
         self.templating_utils[name] = function
 
     def registerUtilMethod(self, name, function):
@@ -275,6 +285,16 @@
            `self` is a TemplatingUtils object. You can use self.client
            to access the client object for your request.
         """
+        # prevent overriding of internal TemplatingUtil methods/vars.
+        if name.startswith('_'):
+            import inspect
+            caller = inspect.stack()[1]
+            raise ValueError(
+                "Can't define template utility method named '%(name)s' at:\n"
+                "   %(filename)s:%(lineno)d\n"
+                "   Utility method names must not start with '_'.\n"
+                % {**caller._asdict(), "name": name})
+
         setattr(self.TemplatingUtils,
                 name,
                 function)