Summary

Phase A of the data grid clean-architecture refactor. Self-contained, low-risk: extracts the four cell-focus / range-selection ints from KeyHandlingTableView into a single TableSelection value type.

Why

KeyHandlingTableView owned four loose stored properties (focusedRow, focusedColumn, selectionAnchor, selectionPivot) plus two separate didSet blocks that each computed partial reload indices. The blocks were almost-but-not-quite redundant:

• focusedRow.didSet reloaded only the OLD row, relying on selection-change to redraw the new row
• focusedColumn.didSet reloaded BOTH columns at the current row

Inconsistent enough to be subtle. Hard to test (state lives on a UIView).

What changed

• New TableSelection: Equatable value type (focusedRow, focusedColumn, anchor, pivot, plus setFocus, clearFocus, resetAnchor, clearAnchor, hasFocus)
• TableSelection.reloadIndexes(from:) returns the (rows, columns) IndexSet pair needing redraw on a transition
• KeyHandlingTableView holds one selection: TableSelection; its didSet calls reloadIndexes and reloads
• The four old properties are kept as computed accessors that mutate selection (no churn at call sites)

Tests

17 unit cases for TableSelection covering: defaults, focus mutation, anchor/pivot lifecycle, equatable, and every transition path through reloadIndexes (no change, anchor-only, initial focus, clearing focus, row change, column change, both change).

Files

• TablePro/Views/Results/TableSelection.swift (new)
• TablePro/Views/Results/KeyHandlingTableView.swift (state migration)
• TableProTests/Views/Results/TableSelectionTests.swift (new)
• TableProTests/Views/Main/Child/DataTabGridDelegateTests.swift (FakeRowDeltaApplier conforms to existing invalidateCachesForUndoRedo requirement added in refactor(datagrid): interaction fixes, window UndoManager, multi-cell paste #924)

Test plan

• Click a cell, arrow keys move focus, focus border follows
• Shift+arrow extends row range from anchor
• Click row number column clears focus
• Click empty area clears focus
• Tab/Shift+Tab navigates between cells
• No regressions in undo/redo/edit (TableSelection only owns focus + range, not data)