StartSelectionRegionOptions

type StartSelectionRegionOptions = 
  | StartRectangularRegionSupportedOptions
  | StartPolygonRegionSupportedOptions
  | StartRangeRegionSupportedOptions;

Per-call options for SelectionApi.startSelectionRegion, discriminated by the RegionType type. Region-shape props live at the top level (e.g. vertical for a range); options is a raw passthrough escape hatch for everything else.