Owned-self builder pattern (no lifetime parameters). WorkflowBuilder chains start_with/then/end_workflow to produce WorkflowDefinition. StepBuilder supports: name, id, on_error, compensate_with, then, then_fn, wait_for, delay, if_do, while_do, for_each, saga, parallel. ParallelBuilder for branching with join semantics. InlineStep for closure-based steps. Step config stored on WorkflowStep.step_config.