Update D&D schemas to require integer unit_id values

internal/modules/extract/dnd/spells/extractor.go

@@ -133,7 +133,7 @@ func (e *Extractor) Extract(ctx context.Context, req contracts.ExtractionRequest
 		}
 		candidates = append(candidates, artifacts.ArtifactCandidate{
 			Payload:    payload,
-			SourceRefs: append([]source.SourceRef(nil), spellCast.SourceRefs...),
+			SourceRefs: sourceRefCandidates(req.Source, spellCast.SourceRefs),
 		})
 	}
 	return contracts.ExtractionResult{Candidates: candidates}, nil
@@ -164,6 +164,17 @@ func spellCastPayload(spellCast spellCastResponse) (json.RawMessage, error) {
 	})
 }
 
+func sourceRefCandidates(doc *source.SourceDocument, refs []dnd.SourceRefResponse) []source.SourceRef {
+	if len(refs) == 0 {
+		return nil
+	}
+	out := make([]source.SourceRef, 0, len(refs))
+	for _, ref := range refs {
+		out = append(out, dnd.SourceRefCandidate(doc, ref))
+	}
+	return out
+}
+
 func extractorErrorf(format string, args ...any) error {
 	return fmt.Errorf("dnd spells extractor: "+format, args...)
 }