fix: batch admin billing reservations

internal/userbilling/service.go

@@ -1220,6 +1220,7 @@ LIMIT $1`, limit)
 	defer rows.Close()
 
 	users := []adminBillingUserSummary{}
+	userIDs := []string{}
 	for rows.Next() {
 		var item adminBillingUserSummary
 		var lastUsed sql.NullTime
@@ -1236,19 +1237,61 @@ LIMIT $1`, limit)
 			item.APIKeys.LastUsedAt = &value
 		}
 		item.Credits.Available = item.Credits.Balance - item.Credits.Reserved
-		reservations, err := s.activeReservations(ctx, item.User.ID, 5)
-		if err != nil {
-			return nil, err
-		}
-		item.Reservations.Active = reservations
+		userIDs = append(userIDs, item.User.ID)
 		users = append(users, item)
 	}
 	if err := rows.Err(); err != nil {
 		return nil, err
 	}
+	reservations, err := s.activeReservationsForUsers(ctx, userIDs, 5)
+	if err != nil {
+		return nil, err
+	}
+	for i := range users {
+		users[i].Reservations.Active = reservations[users[i].User.ID]
+	}
 	return users, nil
 }
 
+func (s *Server) activeReservationsForUsers(ctx context.Context, userIDs []string, perUserLimit int) (map[string][]reservationSummaryRow, error) {
+	items := map[string][]reservationSummaryRow{}
+	if len(userIDs) == 0 {
+		return items, nil
+	}
+	placeholders := make([]string, len(userIDs))
+	args := make([]any, 0, len(userIDs)+1)
+	for i, userID := range userIDs {
+		placeholders[i] = "$" + strconv.Itoa(i+1)
+		args = append(args, userID)
+	}
+	limitParam := "$" + strconv.Itoa(len(args)+1)
+	args = append(args, perUserLimit)
+	query := `
+SELECT user_id, id, service_id, estimated_credits, estimated_tokens, status, expires_at, created_at
+FROM (
+  SELECT user_id, id, service_id, estimated_credits, estimated_tokens, status, expires_at, created_at,
+         row_number() OVER (PARTITION BY user_id ORDER BY expires_at ASC, created_at DESC) AS rn
+  FROM hwlab_billing_reservations
+  WHERE user_id IN (` + strings.Join(placeholders, ", ") + `) AND status = 'reserved' AND expires_at > now()
+) ranked
+WHERE rn <= ` + limitParam + `
+ORDER BY expires_at ASC, created_at DESC`
+	rows, err := s.db.QueryContext(ctx, query, args...)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	for rows.Next() {
+		var userID string
+		var item reservationSummaryRow
+		if err := rows.Scan(&userID, &item.ReservationID, &item.ServiceID, &item.EstimatedCredits, &item.EstimatedTokens, &item.Status, &item.ExpiresAt, &item.CreatedAt); err != nil {
+			return nil, err
+		}
+		items[userID] = append(items[userID], item)
+	}
+	return items, rows.Err()
+}
+
 func (s *Server) adminBillingTotals(ctx context.Context) (map[string]any, error) {
 	var totals struct {
 		Users              int64