How does durable execution persist workflow state across crashes?

Durable execution persists workflow state by checkpointing the entire execution context—including variables, call stack, and event history—to a durable store after each deterministic step. When a crash or restart occurs, Catalyst replays the checkpointed state from the last completed step, not from the beginning. This ensures no progress is lost, though any side effects from the interrupted step must be idempotent or reconciled by your application logic.