feat(core): add session snapshot and revert system (#33226)

packages/core/test/session-runner-tool-events.test.ts

@@ -125,3 +125,12 @@ test("old success event data containing result still decodes", () => {
   })
   expect(decoded.result).toMatchObject({ type: "content" })
 })
+
+test("step finish records settlement without publishing step ended", async () => {
+  const { published, publisher } = capture()
+  await Effect.runPromise(publisher.publish(LLMEvent.stepStart({ index: 0 })))
+  await Effect.runPromise(publisher.publish(LLMEvent.stepFinish({ index: 0, reason: "stop" })))
+
+  expect(published.some((event) => event.type === "session.next.step.ended.2")).toBe(false)
+  expect(publisher.stepSettlement()).toMatchObject({ finish: "stop" })
+})