fix: daily vani

internal/repository/vani_repo.go

@@ -88,19 +88,20 @@ func (r *VaniRepo) Insert(ctx context.Context, pick *model.VaniPick) error {
 }
 
 // BookTitle resolves a book code to its display title (from book_meta.data.title),
-// or "" if unknown. Used to label a prose pick with its book name.
+// or "" if unknown. Used to label a prose pick with its book name. Decoding into
+// a typed struct avoids the bson.M-nested-doc pitfall (nested documents decode
+// as bson.D, so a `raw["data"].(bson.M)` assertion would silently fail).
 func (r *VaniRepo) BookTitle(ctx context.Context, book string) string {
-	var raw bson.M
+	var doc struct {
+		Data struct {
+			Title string `bson:"title"`
+		} `bson:"data"`
+	}
 	if err := r.mongo.Collection("book_meta").
-		FindOne(ctx, bson.D{{Key: "book", Value: book}}).Decode(&raw); err != nil {
+		FindOne(ctx, bson.D{{Key: "book", Value: book}}).Decode(&doc); err != nil {
 		return ""
 	}
-	if data, ok := raw["data"].(bson.M); ok {
-		if t, ok := data["title"].(string); ok {
-			return t
-		}
-	}
-	return ""
+	return doc.Data.Title
 }
 
 // --- Mongo: random candidate sampling ---