Change internal state of entity inside an aggregate root

Question

Im developing a bank system that uses event sourcing.

I have an aggregate root named Account:

BankAccount {

    private var balance: BigInteger = BigInteger.ZERO
    private val transactions = mutableListOf<Transaction>()
    private var revision: Long = 0

The Transaction entity:

Transaction(val amount: BigDecimal, status: TransactionStatus) {

    val id: UUID = UUID.randomUUID()
    var status: TransactionStatus = TransactionStatus.REGISTERED

Register a new transaction in bankAccount aggregate root is very simple, but I also have to confirm or to cancel the transaction after some asynchronous validation.

The problem starts when I need to fetch the registered transaction in order to change it state:

fun completeTransaction(transactionId: UUID, newStatus: TransactionStatus){
  val transaction = transactions.first { it.id == transactionId }

  transaction.changeStatus(newStatus)
} 

First problem: Searching the transaction could impact performance given the number of transactions in the list.

In order to solve that, I can implement a snapshot solution, but how to garantee that the list of transaction will have the transaction with status REGISTERED that needs to change status in order to complete it? Because I cant pass the entire list to every snapshot. Its not performatic

Im thinking in transform the Transaction entity to a Transaction Aggregate Root instead. Then my stream will be very short. Use the bankaccount AR to validate balance and a Transaction AR to validate transaction state.

SOLVED

I change the implementation of completeTransaction function. Everytime a transaction is completed I remove the transaction from the list. So now I can always save the transaction list in the snapshot because it will always contains only UNCOMPLETED transactions