Session keeps a window list (stable ids, per-window selection, active sheet
and per-sheet selections swapped into the workbook without dirtying it)
in place of the index-based hidden list and the copying New Window.
Titles read Name:1 / Name:2 for a workbook with several windows.
File > Close closes one window of several; window.close, window.list and
window ids for window.activate, view.switchWindows, view.hideWindow and
view.unhideWindow. Control channel and MCP tools take window/doc ids;
scroll positions and cell drafts belong to their window.
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