ConstThe extension is the one surface that puts a person in the grid beside the agent, and nothing else in the report can see it until a workbook is already open there. This looks for the editor itself, so an agent can offer the extension to someone who has VS Code and has never heard of it.
Local file reads only, and best-effort in both directions: a portable install with no launcher on PATH and no profile directory reports as absent, and an extension uninstalled since the editor last restarted still has its directory and reports as installed.
Whether VS Code is on this machine, and whether the SheetXL extension is installed in it.