fix(concurrency,durability): address Opus review critical findings

- create_queue: SaveQueue under per-queue lock, not global SyncQueues.Lock
  (fixes fatal concurrent map iteration/write on idempotent CreateQueue of existing FIFO queue)
- delete_message_batch: reject empty ReceiptHandle (JSON protocol bypass deleted all unreceived msgs)
- send_message/send_message_batch: register dedupId only after successful persist
  (retry with same dedupId no longer returns 200 without persisting)
- memory_guard: global HeapAlloc guard (SHARED_SQS_MAX_HEAP_MB, 0=off) in send paths

app/gosqs/send_message_batch.go

@@ -111,9 +111,14 @@ func SendMessageBatchV1(req *http.Request) (int, interfaces.AbstractResponseBody
 	if queue.LiveCount()+len(sendEntries) > MaxMessagesForQueue(queue.IsFIFO) {
 		return utils.CreateErrorResponseV1("OverLimit", true)
 	}
+	// Глобальный предохранитель памяти (HeapAlloc) — защита от OOM суммой тенантов.
+	if heapOverLimit() {
+		return utils.CreateErrorResponseV1("OverLimit", true)
+	}
 
 	newMsgs := make([]models.SqsMessage, 0, len(sendEntries))
 	appendedIdx := make([]int, 0, len(sendEntries))
+	appendedDedupIDs := make([]string, 0, len(sendEntries))
 	for _, sendEntry := range sendEntries {
 		msg := models.SqsMessage{MessageBody: sendEntry.MessageBody}
 		if len(sendEntry.MessageAttributes) > 0 {
@@ -133,10 +138,10 @@ func SendMessageBatchV1(req *http.Request) (int, interfaces.AbstractResponseBody
 		if !queue.IsDuplicate(sendEntry.MessageDeduplicationId) {
 			appendedIdx = append(appendedIdx, queue.AppendMessage(msg))
 			newMsgs = append(newMsgs, msg)
+			appendedDedupIDs = append(appendedDedupIDs, sendEntry.MessageDeduplicationId)
 		} else {
 			log.Debugf("Duplicate deduplicationId [%s] in queue [%s]", sendEntry.MessageDeduplicationId, queueName)
 		}
-		queue.InitDuplicatation(sendEntry.MessageDeduplicationId)
 
 		sentEntries = append(sentEntries, models.SendMessageBatchResultEntry{
 			Id:                     sendEntry.Id,
@@ -157,6 +162,11 @@ func SendMessageBatchV1(req *http.Request) (int, interfaces.AbstractResponseBody
 		}
 		return utils.CreateErrorResponseV1("InternalError", true)
 	}
+	// Регистрируем dedupId ТОЛЬКО после успешной записи — иначе ретрай с теми же
+	// dedupId получил бы 200 без сохранённых сообщений.
+	for _, id := range appendedDedupIDs {
+		queue.InitDuplicatation(id)
+	}
 	// Метаданные очереди (FIFO state, duplicates) — без Messages
 	persistence.SaveQueue(key, queue)