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Interview question · Agent, Tool & MCP Security

A customer-support agent can issue refunds. Which checks must live outside the model, and how do you stop abuse?

Design a refund ledger that handles authorization, concurrent reservations, distinct partial refunds and uncertain provider outcomes. A stable retry key helps, but does not enforce the business budget.

hardNewUpdated Nov 2026

Design a refund ledger that handles authorization, concurrent reservations, distinct partial refunds and uncertain provider outcomes. A stable retry key helps, but does not enforce the business budget.

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  1. 01 State the assumptions your answer depends on.
  2. 02 Explain the mechanism and choose a control.
  3. 03 Name a condition that would change your decision.

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What if · the follow-ups in this answer

The answer works through 4 follow-ups like an interviewer would

Alder has a payment of 120 units, 30 already refunded and 20 reserved. Two distinct requests each propose another refund of 50.

  1. Can both requests reserve their requested amount?
  2. Should two partial refunds in one conversation use the same operation ID?
  3. What if the provider times out after accepting one refund?
  4. What should the acceptance test demonstrate?

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