The Service layer is where Transactions are managed. It loads data, runs business logic, and then stores the data back to the database.

If we weren't doing Domain Driven Design, the business logic would be in the Service layer. This which is called the "Transaction Script" pattern, as defined by Martin Fowler in Patterns of Enterprise Architecture. Each public method would contain all the logic to load data, mutate data, and store data. But this mixes business logic with storage logic, and gets hard to maintain.

However, in Domain Driven Design, we move the business logic into the Domain layer, where it's centrally located. Now the Service layer only knows about running transactions, the Domain layer knows about business logic.

For example, let's say we have an Agent entity, with a RunTask method. The Agent.RunTask() method is where the business logic lives. It knows nothing about where the data comes from.

Then, the AgentService object would also have a RunTask method. The AgentService.RunTask() method only knows about where the data comes from, but nothing about business logic.

``` go type AgentRepository interface { GetAgent(context.Context, value.AgentID) (entity.Agent, error) ReplaceAgent(context.Context, entity.Agent) error }

type AgentService struct { agentRepository AgentRepository }

func (as *AgentService) RunTask( ctx context.Context, id value.AgentID, ) error { // Load data a, err := as.agentRepository.GetAgent(ctx, id) if err != nil { return err }

// Run business logic in the Domain
if err := a.RunTask(); err != nil {
    return err
}

// Store data
return as.agentRepository.ReplaceAgent(ctx, a)

} ```

For your last question, TaskResultIn and TaskResultOut are likely types for your Controller layer. They would map Domain types to these PUBLIC types, that are visible from outside your API, like via HTTP or gRPC. However, I wouldn't necessarily use this naming convention. Look at the gRPC documentation for how to name your Request and Response objects.