A sentinel value for "the data layer tried to determine this and couldn't, in its current view of the graph" — complementary to Ash.NotLoaded.

Ash.NotLoaded marks a value that simply hasn't been fetched yet — ask again and it resolves. AshNeo4j.Unknown marks a value the read genuinely reached for and could not determine — e.g. a reached node whose labels don't resolve to a known resource, or a value a future store reports as indeterminate. Both are explicit values: consumers pattern-match Unknown, nil, and concrete values as distinct outcomes, and never read nil-meaning- absent into an Unknown.

It deliberately implements no String.Chars/Inspect-coercion that would let it pass quietly as a value — use it where a value is expected and it stays loud; acknowledge it and it's calm.

Shape

%AshNeo4j.Unknown{
  world:   MyApp.SomeResource,   # the (Domain, Resource) frame of the original query
  reason:  :reached_unresolved,  # a leaf atom, OR a nested unknown from a deeper layer
  context: %{label: :Foo, …}     # local diagnostics, not load-bearing
}

• :world — the (Domain, Resource) frame the query was asked in, stored as the resource module (the Domain is derivable via Ash.Resource.Info.domain/1). It is the frame the caller is standing in — not the thing that failed to resolve (that belongs in :reason/:context). The Domain alone is insufficient: within one Domain multiple resources can share a base label, so Domain + Resource together identify the frame.

• :reason — either a leaf atom() or a nested unknown from the layer beneath. The cause of not-knowing can be a deeper not-knowing: an AshNeo4j.Unknown raised at the data-layer boundary can carry, as its reason, a store's own indeterminate value, and an outer world (e.g. a consumer's Diffo.Unknown) can in turn carry this one. Outer holds inner by value, following the dependency direction — no module coupling, no cycles. The chain bottoms out in an atom. The atom vocabulary is library-structural and documented where each Unknown is produced; there is no central registry.

• :context — term(), local diagnostics for this layer (the unresolved label, the hop chain, …). Never the place the cause lives.

Frame-lifting at the boundary

ash_neo4j is the layer that turns a frameless or store-native unknown into an Ash-framed one: it stamps :world with the resource being read and, where the unknown originated beneath it, carries that inner unknown as :reason. A store has no concept of a Domain/Resource pair, so its :world may be store-native or absent — this struct never assumes the thing it nests shares its notion of a world.