OptionaldryDry run mode: no tool is called, each step waits its
estimatedDuration and completes with the result { dryRun: true }
OptionalonCalled after a checkpoint was created
OptionalonCalled after each completed step
OptionalonCalled with the result of each completed step
OptionalresumeResume from a checkpoint ID. Needs a CheckpointManager; without one the option is ignored.
Options for WorkflowEngine.execute.