pub fn diff_columns(table: &TableSpec, live: &[LiveColumn]) -> Vec<ColumnDiff>Expand description
Columns present in table but absent from live (matched by name).
Reports only missing (kit-but-not-live) columns. Live-only columns and
type differences are ignored — they are not this additive path’s concern.
Each ColumnDiff::ch_type is computed from the table column’s own trusted
[ColumnTypeSpec::to_ch_type], never from the live introspection.