Event bus internals

EventBus is an in-process publish/subscribe component shared through Arc. Subscribers are grouped by EventType in a concurrent map, and published events are retained in an in-memory history grouped by type.

Publication path

Event
  |-- increment total count
  |-- append to per-type history
  `-- invoke matching handlers in the publisher's thread

Handlers are synchronous Fn(&Event) callbacks. A slow handler delays the publisher. A panicking handler can unwind through publish; panic isolation and asynchronous delivery are not implemented by the current bus. Handlers must therefore stay fast, non-blocking, and panic-free.

Correlation and ordering

• Every event has an event ID, correlation ID, timestamp, version, source, severity, type, and string data map.
• Correlation queries scan all retained history.
• get_events_sorted sorts a snapshot by timestamp.
• get_all_events does not promise cross-type insertion order.
• clear_history removes retained events but does not reset the lifetime event counter.

Lifecycle and limits

History is unbounded until explicitly cleared. There is no persistence, replay cursor, backpressure, delivery acknowledgement, or cross-process transport. Hosts that need those properties should subscribe with a small adapter and move work to a bounded external queue.

Adding a durable broker must not change the domain Event contract merely to expose a transport implementation. Record such a boundary change in an ADR.