`unsloth studio update --local 2>&1 | tee logs/update.log` was
producing an empty update.log on windows-latest because
_run_setup_script() invoked powershell.exe -File studio/setup.ps1.
setup.ps1 emits every step/substep line via Write-Host, which on
PowerShell 5+ lands on the Information stream (#6) and is NOT
merged into stdout when -File is used and the parent's stdout is a
pipe. The bash tee in CI therefore saw nothing, and the post-step
grep for "prebuilt up to date and validated" failed with
::error::no prebuilt up-to-date marker in update.log.
Switch the Windows branch from -File to -Command, with the script
path single-quoted (apostrophes escaped per PowerShell rules) and
followed by *>&1 so all six PS streams (stdout, stderr, warning,
verbose, debug, information) are merged into the success stream.
That stream is then inherited by the Python subprocess and reaches
the parent's stdout pipe verbatim.
This also makes the install.ps1 -> unsloth.exe -> setup.ps1
grandchild output visible at install time for the first time, so
logs/install.log gains the existing "prebuilt installed and
validated" marker. The Windows-update workflow's filesystem-based
fallback is unchanged and still works.
Mac is untouched (still uses bash setup.sh -- plain stdout).
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