Agent Times Issuing Refund Question Explained
This worked AI Engineer Interview practice question tests System Reasoning. Try the answer first, then review why A is the best choice.
Short answer
The correct answer is A. An idempotency key on the side-effecting operation, so a replay returns the original result instead of re-executing..
A timeout means the client doesn't know whether the operation succeeded — the only safe retry is one the server can recognize as a replay, which is what an idempotency key provides. The key is to match the exact action in the prompt to the tool, command, or concept that performs that action directly. Here, A. An idempotency key on the side-effecting operation, so a replay returns the original result instead of re-executing. is the only option that satisfies the scenario without adding unrelated behavior.
The Question
An agent times out after issuing a refund, retries, and issues a second refund. Which system property was missing?
Why A is correct
A timeout means the client doesn't know whether the operation succeeded — the only safe retry is one the server can recognize as a replay, which is what an idempotency key provides. The key is to match the exact action in the prompt to the tool, command, or concept that performs that action directly. Here, A. An idempotency key on the side-effecting operation, so a replay returns the original result instead of re-executing. is the only option that satisfies the scenario without adding unrelated behavior.
Why the other options are wrong
Option B does not match the requirement in the prompt. The correct answer is A because A timeout means the client doesn't know whether the operation succeeded — the only safe retry is one the server can recognize as a replay, which is what an idempotency key provides.
Option C does not match the requirement in the prompt. The correct answer is A because A timeout means the client doesn't know whether the operation succeeded — the only safe retry is one the server can recognize as a replay, which is what an idempotency key provides.
Option D does not match the requirement in the prompt. The correct answer is A because A timeout means the client doesn't know whether the operation succeeded — the only safe retry is one the server can recognize as a replay, which is what an idempotency key provides.
Key idea: System Reasoning
Every question is a production situation an AI engineer interviewer can put to you: a failing endpoint, a cost spike, an agent that loops, an eval that disagrees with users. The best answer is almost always the one that measures or contains the problem before it changes the model or the prompt. If you miss a question, note which habit it tests: decompose before you fix, put the security boundary where the side effect happens, and trust an eval only after you check what it covers. The 12 open-ended questions with answer guides are at aijobprep.app/questions/ai-engineer.html.
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