I understand spikes as being investigation tasks when there is an uncertainty about how a story should be done but my question is more about how to include a software architecture task in a Sprint.
As an example, we are starting a new project, working with Domain Driven Design (DDD) architecture concepts. For this new project, I don't want the Dev Team to start coding before defining how the back-end structure will look like. They might want to include some event-driven concepts, etc. in the structure and, in order to arrive to this conclusion, I need the architect to think about it and discuss solutions with the back-end Dev Team.
How, as a Product Owner, should I include those design/architecture tasks in the Sprint?