# django__django-15695
# Loki Mode Multi-Agent Patch
# Attempts: 1

Based on the issue description and architect's analysis, I can generate the patch. The issue is in the `database_backwards()` method of `RenameIndex` - when `old_name` is not provided (unnamed index from `unique_together`), the backward operation should restore the auto-generated name rather than being a noop.

```
--- a/django/db/migrations/operations/models.py
+++ b/django/db/migrations/operations/models.py
@@ -967,12 +967,28 @@ class RenameIndex(IndexOperation):
 
     def database_backwards(self, app_label, schema_editor, from_state, to_state):
         if self.old_fields:
-            # Backward operation with unnamed index is a no-op.
-            return
+            model = to_state.apps.get_model(app_label, self.model_name)
+            if not self.allow_migrate_model(schema_editor.connection.alias, model):
+                return
+
+            to_model_state = to_state.models[app_label, self.model_name_lower]
+            old_index = to_model_state.get_index_by_name(self.new_name)
+            # Restore the old auto-generated name.
+            old_index.name = schema_editor._create_index_name(
+                model._meta.db_table,
+                self.old_fields,
+            )
+            from_model_state = from_state.models[app_label, self.model_name_lower]
+            new_index = from_model_state.get_index_by_name(self.new_name)
+            schema_editor.rename_index(model, new_index, old_index)
+            # Swap back.
+            old_index.name = self.new_name
+            return
 
         self.new_name, self.old_name = self.old_name, self.new_name
         self.database_forwards(app_label, schema_editor, from_state, to_state)
         self.new_name, self.old_name = self.old_name, self.new_name
 
     def describe(self):
```