NOTE
Layered Architecture
Separating presentation/application/domain/infrastructure responsibilities while controlling dependency direction.
This is a historical learning note and may contain outdated or incomplete understanding.
Layered architecture organizes responsibilities into levels such as presentation/API, application orchestration, domain logic, and infrastructure/persistence.
The useful rule is dependency control: higher-level business policies should not become tightly coupled to database/web/framework details. Interfaces/adapters can keep domain/application decisions testable and replaceable.
Too many pass-through layers create ceremony. Define layers around real responsibility/dependency boundaries rather than requiring every request to touch a fixed number of classes.