src/observer/hub.rs

This file holds EventHub, an adapter that turns one LoopObserver into a broadcast stream. You register the hub as an observer and subscribe from anywhere.

That gives you many consumers, in other tasks, such as a CLI rendering an attached run.

Key items

EventHub::new(capacity) builds your bounded broadcast channel, and subscribe() hands out receivers to you freely.

LoopEvent has one variant per engine event, each carrying the observer context’s payload. It is #[non_exhaustive] with an Unknown variant that forwards future kinds’ raw envelopes, so an old consumer never breaks on a new event.

ObservedEvent is the envelope you receive: the event plus run/turn metadata and the hub’s emission sequence.

Behavior notes

Lagged receivers are dropped, not buffered. The channel is bounded, so a slow consumer that falls behind loses its oldest events, because the hub favors the live run over the laggard.

A consumer that must not miss anything persists from the event ledger instead, which is memory::trajectory’s EventLedgerObserver writing events.jsonl.

You also get the new 0.4.0 events forwarded: GateDecision, BudgetWarn, PreCompaction, CompactionFailed, and AttemptReset, each mapped to its kind in call order.

For the deep dive, see The event hub.