Application

The use case lives at lib/src/application/notes/. Ports that are not domain concepts, the clock and the id generator, live at lib/src/application/ports/ so every feature's workflows can share them.

SaveNoteUseCase.execute does one thing. It asks Note.create for a note, then returns whatever NoteRepository.save returns. The adapter reads the row back, so the caller sees the timestamp that survived createdAtMicros. The use case does not catch ValidationFailure. Presentation maps that failure.

Future<Note> execute({required String title, required String body}) {
  final note = Note.create(
    id: _ids.newId(),
    title: title,
    body: body,
    now: _clock.now(),
  );
  return _notes.save(note);
}

ListNotesUseCase calls findAll. Two intents, two classes. The clock and the id generator are ports beside the use case, so a test can pass a fixed instant and a fixed id. The source is lib/src/application/notes/save_note_use_case.dart.

The use case constructor takes NoteRepository. It never mentions NoteRepositoryImpl.

Next: Infrastructure.