Can the assistant move £390 from this account?
Check posted money, active holds and duplicate transfer commands.
“we evaluate your own logic, reasoning, and critical thinking” (opens the source)
The question
Meridian Pay’s fictional account has a £500 posted balance and a £120 active card hold. It has no overdraft. An AI draft recommends a £390 internal transfer by looking only at posted balance. Available balance equals posted balance minus active holds.
| Amount (£) | |
|---|---|
| Posted balance | 500 |
| Active card hold | 120 |
| Requested transfer | 390 |
The card hold has not yet been posted as a debit.
For a new internal transfer command, check available funds and post the source debit and destination credit atomically. One command ID has one stored result. A replay returns that result; a different command must pass a new balance check.
“Choose your next action and explain the evidence behind it.”
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A strong answer, step by step
Open each step in turn. This is one strong answer, not the only one.
Step 1: Find the spendable amount
What would you do here? Open the move you’d make.
Check the £380 available balance.
The strong move. An active hold reserves money that is still in the posted balance.
Approve because £390 is below £500.
Tempting, but it misses something. The draft ignores the £120 already reserved by the card hold.
See how a strong candidate says it
“Available balance is £500−£120 = £380. The £390 request exceeds that by £10, so it cannot proceed in this state.”
Why it works: An active hold reserves money that is still in the posted balance.
Step 2: Use the ledger as authority
What would you do here? Open the move you’d make.
Validate and post through the ledger’s atomic operation.
The strong move. The check and update must agree on one account state.
Check the balance first, then post later without a guard.
Tempting, but it misses something. Another transaction could use the same available money between that check and the debit.
See how a strong candidate says it
“I would read the ledger’s current state, then validate and post a new transfer in one atomic operation. An AI summary cannot reserve funds or make a stale balance safe.”
Why it works: The check and update must agree on one account state.
Step 3: Recalculate after settlement
The card settles for £110 and the full £120 hold is released. Two queued deliveries of the same £390 transfer command, move-7, now wait to be processed.
What would you do here? Open the move you’d make.
Recalculate both posted balance and active holds.
The strong move. A hold release and a posted debit are different movements.
Subtract both the old hold and the new £110 debit.
Tempting, but it misses something. The full hold was released; subtracting it again would reserve money twice.
See how a strong candidate says it
“The card debit reduces posted balance to £390. Releasing the £120 hold leaves no active holds, so £390 is available. The requested transfer now fits exactly.”
Why it works: A hold release and a posted debit are different movements.
Step 4: Move the money once
What would you do here? Open the move you’d make.
Return the stored result for the duplicate command.
The strong move. A repeated command is not another transfer.
Post both deliveries because each arrived separately.
Tempting, but it misses something. Two deliveries carry one command ID; a second debit would violate the ledger rule.
See how a strong candidate says it
“The first move-7 posts one £390 debit and one £390 destination credit, leaving £0 in the source. The second delivery returns the stored result. It does not post another debit.”
Why it works: A repeated command is not another transfer.
The answer, in short
- Decision
- Allow one transfer after settlement, then replay its stored result.
- Because
- The new state has exactly £390 available and move-7 represents one transfer.
- What would change it
- A different command, a new hold or a changed posted entry would require a fresh funds check.
Common traps
- Treating posted balance as available balance.
- Posting a duplicate command twice.
Check your answer
- I subtracted the active hold.
- I kept the funds check atomic with posting.
- I released the hold when the card settled.
- I posted one balanced transfer.
Last reviewed Nov 10, 2026