Function pure_data_kind 

pub fn pure_data_kind(kind: &str) -> bool

Step kinds that are PURE data transforms: no external effect, no durable write of their own, fully deterministic over the run’s data. The checkpoint-before-effect rule exists to stop a crash from losing or repeating an effect, and these steps have none — a crash simply replays them from the last checkpoint and reaches the same values. So the scheduler skips the checkpoint for them, and an inline chain batches into its tick’s single checkpoint instead of paying a serialize-and-write per step, which measures at roughly 40% of such a chain’s cycles.