Both emitted PowerShell scripts opened with `$home=<hermesHome>`; $HOME is a
read-only automatic variable, so real powershell.exe throws 'Cannot overwrite
variable HOME' and the update-marker probe exits 1 without ever printing CLEAR —
previously masked by the parse error this PR fixes (found by the live pass on
windows-latest). Rename to $hermesHome and add the read-only-variable
assignment check to the emitted-script test.