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Code RoomRetry logic double charges
HardPrep Room Coding #4064

Retry logic double charges

Vibe & agenticNetworking & APIsSenior–Staff~18 min

An AI assistant wrote this Go client wrapper to make a POST to a payment provider resilient by retrying on failure. It passed integration tests against a mock that never timed out. In production, a small number of customers were charged twice.

Why did some customers get double-charged, and how do you make retries safe?

Implement
count_committed_charges(attempts: list[str]) → int
Examples
in[["ord_1|k1|timeout","ord_1|k1|timeout","ord_1|k1|ok"]]out1
in[["ord_1|k1|timeout","ord_1|k2|timeout","ord_1|k3|ok"]]out3
in[["ord_1||timeout","ord_1||ok"]]out2
What a strong answer looks like

Treat the AI’s output as a draft to verify, not an answer to trust. Name the specific flaw and the input that triggers it, say how you’d catch it (tests, edge cases, reading critically), and how you’d re-prompt or decompose to get it right.

0:00 of about 18 min

Vibe & agentic: describe the solution in plain language (or narrate it) and the coach grades your approach.

Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.