- The runner has Windows PowerShell 5.1, not pwsh/PowerShell 7 — switch all
steps from `shell: pwsh` to `shell: powershell`.
- Make the scripts 5.1-safe: force TLS 1.2 for HTTPS, -UseBasicParsing on
Invoke-WebRequest, and write GITHUB_ENV as ascii (no BOM).
- Add a fast `preflight` job that validates the runner (OS, PowerShell, Python
availability) in seconds; build-windows now `needs: [preflight]`.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>