fix: harden backend synchronization

exec/handlers/create.php

@@ -8,8 +8,14 @@ return static function (AppContext $ctx): void {
             $ctx->requireCsrf('create');
             $input = normalize_rule_post($_POST);
             $rule = attach_rule_scope($ctx, RuleValidator::validate($input, $ctx->settings));
-            $ctx->rules->create($ctx->daUser->username(), $rule);
-            $ctx->syncActiveBackend();
+            enforce_rule_backend_constraints($ctx, null, $rule);
+            $created = $ctx->rules->create($ctx->daUser->username(), $rule);
+            try {
+                $ctx->syncActiveBackend();
+            } catch (Throwable $syncError) {
+                $ctx->rules->delete($ctx->daUser->username(), (string)$created['id']);
+                throw $syncError;
+            }
             Http::redirect($ctx->url('index.html', ['status' => 'created']));
         } catch (Throwable $e) {
             $errors[] = $e->getMessage();