12.56Design checklist

Whenever you see a write operation, ask:

What uniquely identifies the entity?

What uniquely identifies the operation?

Can the caller retry?

Can the broker redeliver?

Can two workers process it simultaneously?

Can downstream commit but response be lost?

Does downstream support native idempotency?

Can I enforce uniqueness atomically?

Does ordering matter?

What other side effects occur?

How long should dedupe state live?

How do I recover PROCESSING/unknown state?

This is exactly how a senior integration developer thinks.