fix: add pessimistic lock when fetching next qs batch and marking failed

app/Http/Controllers/Backend/QsController.php

@@ -19,6 +19,7 @@ public function getBatches(Request $request): \Illuminate\Http\Response
                 ['failed', '=', false]
             ])
                 ->orderBy('id')
+                ->lockForUpdate()
                 ->first();
 
             if ($oldestBatch === null) {

app/Jobs/CreateQueryserviceBatchesJob.php

@@ -72,12 +72,20 @@ private function getNewEntities(int $latestCheckpoint): array
 
     private function tryToAppendEntitesToExistingBatches(array $entityIdsFromEvents, int $wikiId): bool
     {
+        if (DB::transactionLevel() < 1) {
+            throw new \Exception(
+                'This method can only be run within the context of a transaction.'
+            );
+        }
+
         $notDoneBatches = QsBatch::where([
             ['done', '=', 0],
             ['pending_since', '=', null],
             ['failed', '=', false],
             ['wiki_id', '=', $wikiId],
-        ])->get();
+        ])
+            ->lockForUpdate()
+            ->get();
 
         foreach ($notDoneBatches as $qsBatch) {
             $entitiesOnBatch = explode(',', $qsBatch->entityIds);

app/Jobs/RequeuePendingQsBatchesJob.php

@@ -35,6 +35,7 @@ private function markBatchesFailed(): array
                 ['done', '=', false]
             ])
                 ->select('id')
+                ->lockForUpdate()
                 ->get()
                 ->pluck('id')
                 ->toArray();