computedColumnIds

Ids of columns whose cells are computed — i.e. columns carrying a joyfill.table.Column.formulas binding. Computed cells derive their value from the row's other cells and are not hand-editable; the grid and the row form both read this one set so they can never disagree on which cells are read-only. Static per table schema, published here beside hiddenCellColumnIds so render paths have a single per-row source.