The Windows Install step ran `& $script` inside a `shell: pwsh` step, so
install.ps1 was executing under PowerShell 7. A genuinely clean Windows box
does not have PowerShell 7: Windows ships powershell.exe (Windows PowerShell
5.1) and pwsh is a separate install that the hosted runner image happens to
preinstall. So the one workflow whose premise is a machine that has never seen
a developer toolchain was testing the installer under a shell that machine
would not have, and no other Windows job anywhere in .github exercises
install.ps1 under 5.1.
Invoke it the way the desktop does (install.rs:325-339, and the bundled
installer step in desktop-app-clean-machine-ci.yml): powershell.exe with
-NoLogo -NoProfile -NonInteractive -ExecutionPolicy Bypass -File. The pwsh
step wrapper stays, since it is only the installer that has to be under 5.1.
Calling powershell.exe with `&` keeps the output in the pipeline, so
Tee-Object still fills logs/install.log, and $LASTEXITCODE after the pipeline
is the child's real exit code, so $rc and `exit $rc` are unchanged.
install.ps1 and studio/setup.ps1 hold no PowerShell 7-only constructs: no
`#Requires` above 5.1, no `&&`/`||` chain operators, no ternary, no
null-coalescing, no ForEach-Object -Parallel, no $IsWindows/$PSStyle, and no
6+ cmdlets or parameters. setup.ps1 declares `#Requires -Version 5.1`, and its
three $PSVersionTable branches gate a 7-only preference on the 7 side with a
5.1 fallback. Every Invoke-WebRequest already passes -UseBasicParsing, which
5.1 needs because it otherwise reaches for the IE engine.
b8a052080e