How do cancellation and idempotency change the way you design background jobs?

if (await _processedJobs.ExistsAsync(job.Id, ct))
    return;

await _paymentProvider.CaptureAsync(job.PaymentId, idempotencyKey: job.Id.ToString(), ct);
await _processedJobs.MarkProcessedAsync(job.Id, ct);

The idempotency key lets the external provider treat retried calls as the same logical operation.

• How would you avoid sending the same email twice?
• What is a poison job?
• When should a cancelled job be retried?
• How do you reconcile unknown payment status?

Look for real workflow safety. Strong answers mention idempotency, retries, durable state, and cancellation boundaries.

This checks whether the candidate can build reliable background processing, which is common in backend systems.