Capstone: An Event Bus

In this capstone, design an event bus for one app process. An event bus distributes an announced event to interested subscribers without requiring the publisher to name them.

The exercise is about guarantees: ordering, delivery, ownership, failure, and resource limits. It is not a durable cross-process message queue.

1. Start with a precise interface

publish(event) -> admission result
subscribe(eventType, deliveryContext, handler) -> subscription
cancel(subscription)
close() -> completion

Use typed events