Update D&D prompt definitions to shallow asset paths

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

@@ -11,12 +11,31 @@ import (
 	"time"
 )
 
-func modulePromptFS() (fs.FS, error) {
-	return promptMapFSFromEmbedded(map[string]string{
-		"assets/prompts/dnd.spells.yaml":            "assets/prompts/dnd.spells.yaml",
-		"assets/prompts/dnd/spells/task.md":         "assets/prompts/task.md",
-		"assets/prompts/dnd/spells/instructions.md": "assets/prompts/instructions.md",
+func modulePromptFS(shared fs.FS) (fs.FS, error) {
+	assetFS, err := promptMapFSFromEmbedded(map[string]string{
+		"assets/prompts/dnd.spells/dnd.spells.yaml": "assets/prompts/dnd.spells.yaml",
+		"assets/prompts/dnd.spells/task.md":         "assets/prompts/task.md",
+		"assets/prompts/dnd.spells/instructions.md": "assets/prompts/instructions.md",
 	})
+	if err != nil {
+		return nil, err
+	}
+	assets := assetFS.(promptMapFS)
+	if shared == nil {
+		return assets, nil
+	}
+	for _, name := range []string{
+		"common-dnd-system.md",
+		"common-dnd-transcript.md",
+		"common-dnd-references.md",
+	} {
+		data, err := fs.ReadFile(shared, name)
+		if err != nil {
+			return nil, fmt.Errorf("read shared prompt asset %s: %w", name, err)
+		}
+		assets["assets/prompts/dnd.spells/"+name] = append([]byte(nil), data...)
+	}
+	return assets, nil
 }
 
 func promptMapFSFromEmbedded(files map[string]string) (fs.FS, error) {