Document D&D extractor contract

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

@@ -14,7 +14,6 @@ import (
 )
 
 const Key = "dnd/spells"
-const ArtifactType = "dnd.spell_cast"
 const SchemaVersion = "v1"
 
 const mappingPolicy = "dnd.spells.extract_mapping.v2"
@@ -122,6 +121,9 @@ func (e *Extractor) ReferenceSlots() []contracts.ReferenceSlot {
 }
 
 func (e *Extractor) ManifestMetadata() map[string]any {
+	if e == nil {
+		return nil
+	}
 	metadata := map[string]any{
 		"prompt_id":               PromptID,
 		"prompt_version":          SchemaVersion,