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ADR-0010: App Router files stay thin; views own screens

Status: Accepted

Date: 2026-06-24

Context​

Next.js route files can easily accumulate screen composition, interaction logic, and data transformations, duplicating the FSD views layer.

Decision​

  • app/**/page.tsx and layouts are routing/framework adapters.
  • Full-screen composition lives in views/<Name>View.
  • Route files may read params/search data, call server-only loaders, and pass serialisable values into the view.
  • Route handlers validate transport input and delegate domain work; they do not duplicate NestJS business logic.
  • Framework-required default exports are the exception to the named-component-export rule.

Consequences​

Views remain reusable and testable without pretending Next.js filesystem routes do not exist. Review checklist Route-1/Route-2 enforce central navigation and thin adapters.

Alternatives considered​

  • Inline full pages in every route file — rejected because layer ownership becomes inconsistent.
  • Remove the views layer — rejected because it is already the screen-composition contract for web-player.