I went with placing htis logic at the command level since it plays well with the composite structure, where you don't know whether you are handling one command or many commands, and you want to aggregate all the errors. I didn't leverage the existing support with rails' model errors because that customizing those message is cumbersome (either i18n or using custom validation logic for everything).
- Big simplification of the overall workflow.
- Composite commands store their commands properly, these are undoable now.
- Child commands are excluded from history
Jorge Manrubia