Add D&D refactoring plan and isolate merger results

internal/modules/dnd/register/merge.go

@@ -7,12 +7,21 @@ import (
 
 func appendSpellLists(values []dnd.SpellList) (dnd.SpellList, error) {
 	count := 0
+	present := false
 	for _, value := range values {
+		if value.SpellCasts != nil {
+			present = true
+		}
 		count += len(value.SpellCasts)
 	}
+	if !present {
+		return dnd.SpellList{}, nil
+	}
 	combined := dnd.SpellList{SpellCasts: make([]dnd.SpellCast, 0, count)}
 	for _, value := range values {
-		combined.SpellCasts = append(combined.SpellCasts, value.SpellCasts...)
+		for _, spellCast := range value.SpellCasts {
+			combined.SpellCasts = append(combined.SpellCasts, cloneSpellCast(spellCast))
+		}
 	}
 	return combined, nil
 }
@@ -31,7 +40,9 @@ func appendNPCLists(values []dnd.NPCList) (dnd.NPCList, error) {
 	}
 	combined := dnd.NPCList{NPCs: make([]dnd.NPC, 0, count)}
 	for _, value := range values {
-		combined.NPCs = append(combined.NPCs, value.NPCs...)
+		for _, npc := range value.NPCs {
+			combined.NPCs = append(combined.NPCs, cloneNPC(npc))
+		}
 	}
 	return combined, nil
 }
@@ -105,6 +116,22 @@ func cloneCombatTurn(value dnd.CombatTurn) dnd.CombatTurn {
 	return clone
 }
 
+func cloneSpellCast(value dnd.SpellCast) dnd.SpellCast {
+	clone := value
+	if value.SourceRefs != nil {
+		clone.SourceRefs = append([]source.SourceRef(nil), value.SourceRefs...)
+	}
+	return clone
+}
+
+func cloneNPC(value dnd.NPC) dnd.NPC {
+	clone := value
+	if value.SourceRefs != nil {
+		clone.SourceRefs = append([]source.SourceRef(nil), value.SourceRefs...)
+	}
+	return clone
+}
+
 func cloneNPCInteraction(value dnd.NPCInteraction) dnd.NPCInteraction {
 	clone := value
 	if value.SourceRefs != nil {