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Describe the handoffs
Map which parts of the system need to react to a change and whether that reaction must happen immediately.
Design for repeated and delayed messages
Define what happens if an event arrives twice, out of order, or later than expected. Make ownership of retries and failures explicit.
Keep the system understandable
Document event contracts and add visibility into the flow. If a direct call is simpler and meets the requirement, use it.
A planning guide. The right implementation depends on your system and requirements.
Talk through your next step