ENGINEERING NOTE / 01
Design the exception before the happy path.
A useful workflow has an answer for the day something arrives late, twice, or not at all.
Start with the inconvenient input
List the events that do not fit: an empty field, a duplicate, a changed schema, an unavailable service. For each, decide whether to retry, hold, ask, or stop.
Make the owner visible
An alert is useful only if someone knows it is theirs. Define the decision, the person responsible, and how the unresolved item returns to work.
Leave a way back
Keep correlation IDs and enough context to replay safely. Check that a retry cannot create a second invoice, project, or client message.
A good workflow is something a person can explain, inspect, and change.