Backing calculation for inherited_party DSL declarations.

Traverses AssignmentRelationship by alias to reach source instances, then reads their PartyRef records for the declared source_role. Injected automatically by TransformInheritedRefs — do not reference this module directly; use the inherited_party DSL entity instead.

See Diffo.Provider.Extension.InheritedPartyDeclaration for the DSL options.

Result shape

A list per input record. Each entry corresponds to one source instance reached by the traversal:

• One or more Diffo.Provider.Party values when the source has matching PartyRef records at source_role.
• %Diffo.Unknown{} when the source is reached but carries no PartyRef at source_role.

When no sources are reached at all (e.g. no assignment), the result is []. Unknown is reserved for "we got here but the role isn't declared" — the X-state from the AGENTS.md Diffo.Unknown discipline.

Reason vocabulary

Only one reason is possible here — PartyRef is a universal indirection so no cross-world dispatch is needed (which is why this calc is cleaner than the characteristic equivalents):

• :role_not_declared — source instance reached but its PartyRef records carry no entry at source_role. :context is %{source_id: id, role: source_role}.

:world stamping

TransformInheritedRefs passes the consumer's resource as :world at compile time. Each emitted %Diffo.Unknown{} stamps it.