> idempotency (absurd does this via steps - but would be better handled with the APIs themselves being idempotent, then not using steps

That is very hard to do with agents which are just all probabilistic. However if you do have an API that is either idempotent / uses idempotency keys you can derive an idempotency key from the task: const idempotencyKey = `${ctx.taskID}:payment`;

That said: many APIs that support the idempotency-key header only support replays of an hour to 24 hours, so for long running workflows you need to capture the state output anyways.