Event Streaming

1START ----> TRANSITION_1 ----> TRANSITION_2 ----> TERMINAL
2  |              |                  |
3  +---- emit events on every transition ----+

1import { LOOP_EVENT_TYPES } from "@loop-engine/events";
2import { buildTimeline, replayLoop } from "@loop-engine/observability";
3import { aggregateId } from "@loop-engine/core";
4 
5const audit: Array<{ at: string; type: string; aggregateId: string }> = [];
6 
7eventBus.subscribe(async (event) => {
8  if (
9    event.type === LOOP_EVENT_TYPES.LOOP_STARTED ||
10    event.type === LOOP_EVENT_TYPES.TRANSITION_EXECUTED ||
11    event.type === LOOP_EVENT_TYPES.LOOP_COMPLETED
12  ) {
13    audit.push({
14      at: event.occurredAt,
15      type: event.type,
16      aggregateId: String(event.aggregateId)
17    });
18  }
19});
20 
21const id = aggregateId("EXP-1");
22const instance = await engine.getState(id);
23const history = await engine.getHistory(id);
24if (instance) {
25  const timeline = buildTimeline(instance, history);
26  const replay = replayLoop(definition, history);
27  console.log(timeline.durationMs, replay.valid);
28}

1{
2  type: "loop.transition.executed",
3  loopId: "expense.approval",
4  aggregateId: "EXP-1",
5  transitionId: "approve",
6  fromState: "PENDING_APPROVAL",
7  toState: "APPROVED",
8  actor: { type: "human", id: "manager@acme.com" },
9  occurredAt: "2026-03-13T12:57:01.440Z"
10}

1cd loop-examples/event-streaming
2pnpm install
3pnpm dev