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# selection
Owns active cell, anchor/focus range, row/column/all selection, and name-box anchors.
## State Decision Template
- Source atoms:
- `selectionAtom`: current sheet id, selection kind, and anchor/focus boundaries only.
- `selectionBoundsAtom`: current sheet row/column count used for clamping.
- Derived atoms:
- `activeCellAtom`: active cell for edit focus and keyboard movement.
- `selectionRangeAtom`: normalized display range boundaries.
- `selectionSnapshotAtom`: compact snapshot for adapters that need all derived values at once.
- Commands:
- `setSelectionAtom`
- `setSelectionBoundsAtom`
- `selectCellAtom`
- `selectRowsAtom`
- `selectColumnsAtom`
- `selectAllAtom`
- Scale bound: selection stores boundaries and modes only. It never expands a range into addresses.
- Backend reads: none. Sheet dimensions are passed in by the adapter through `selectionBoundsAtom`.
- Per-cell/per-row/per-col atom risk: forbidden. Row/column/all selection derive bounded ranges from
counts, not from enumerated ids.
- Tests:
- boundary clamping
- range extension without cell enumeration
- row/column/all derived range contracts
- active-cell derivation