TASK: Remove use of save-points for projections

see neos/neos-development-collection#5321 (comment)

the save-point will only be used for REAL projection errors now and never rolled back if catchup errors occur.

With that change in code the save-points are less important because a real projection error should better be thrown at the start before any statements, and even if some statements were issued and a full rollback is done its unlikely that a reactivateSubscription helps that case.

Instead, to repair projections you should replay

Classes/Subscription/Engine/SubscriptionEngine.php

@@ -343,19 +343,17 @@ private function catchUpSubscriptions(SubscriptionEngineCriteria $criteria, Subs
                             $errors[] = Error::forSubscription($subscription->id, $e);
                         }
 
-                        $this->subscriptionStore->createSavepoint();
                         try {
                             $subscriber->projection->apply($domainEvent, $eventEnvelope);
                         } catch (\Throwable $e) {
                             // ERROR Case:
                             $this->logger?->error(sprintf('Subscription Engine: Subscriber "%s" for "%s" could not process the event "%s" (sequence number: %d): %s', $subscriber::class, $subscription->id->value, $eventEnvelope->event->type->value, $eventEnvelope->sequenceNumber->value, $e->getMessage()));
                             $error = Error::forSubscription($subscription->id, $e);
 
-                            // 1.) roll back the partially applied event on the subscriber
-                            $this->subscriptionStore->rollbackSavepoint();
-                            // 2.) for the leftover events we are not including this failed subscription for catchup
+                            // for the leftover events we are not including this failed subscription for catchup
                             $subscriptionsToCatchup = $subscriptionsToCatchup->without($subscription->id);
-                            // 3.) update the subscription error state on either its unchanged or new position (if some events worked)
+                            // update the subscription error state on either its unchanged or new position (if some events worked)
+                            // note that the possibly partially applied event will not be rolled back.
                             $this->subscriptionStore->update(
                                 $subscription->id,
                                 status: SubscriptionStatus::ERROR,
@@ -370,7 +368,6 @@ private function catchUpSubscriptions(SubscriptionEngineCriteria $criteria, Subs
                         }
                         // HAPPY Case:
                         $this->logger?->debug(sprintf('Subscription Engine: Subscriber "%s" for "%s" processed the event "%s" (sequence number: %d).', substr(strrchr($subscriber::class, '\\') ?: '', 1), $subscription->id->value, $eventEnvelope->event->type->value, $eventEnvelope->sequenceNumber->value));
-                        $this->subscriptionStore->releaseSavepoint();
                         $highestSequenceNumberForSubscriber[$subscription->id->value] = $eventEnvelope->sequenceNumber;
 
                         try {

Classes/Subscription/Store/SubscriptionStoreInterface.php

@@ -35,10 +35,4 @@ public function update(
      * @return T
      */
     public function transactional(\Closure $closure): mixed;
-
-    public function createSavepoint(): void;
-
-    public function releaseSavepoint(): void;
-
-    public function rollbackSavepoint(): void;
 }