Discriminated union of domain errors emitted by findNextLessonToRecommend.
Each variant has a kind string and any structured fields the use case
needs to describe what went wrong. The shape carries no information about
HTTP, UI, or any delivery mechanism — adapters translate these to whatever
the actor expects.
Discriminated union of domain errors emitted by
findNextLessonToRecommend.Each variant has a
kindstring and any structured fields the use case needs to describe what went wrong. The shape carries no information about HTTP, UI, or any delivery mechanism — adapters translate these to whatever the actor expects.