message: typed generic (Column<T>) return of windowColumn
diff: @@ -302,7 +302,7 @@ function arrayColumn<T extends Column.Schema>({ array, schema, valueKind }: Colu
  }
  }
  -function windowColumn<T>(column: Column<T>, start: number, end: number) {
  +function windowColumn<T>(column: Column<T>, start: number, end: number): Column<T> {
  if (!column.isDefined) return Column.Undefined(end - start, column.schema);
  if (start === 0 && end === column.rowCount) return column;
  if (!!column.__array && ColumnHelpers.isTypedArray(column.__array)) return windowTyped(column, start, end);
  