The previous Write-Host capture attempts (47432b0b -Command + *>&1
and f2c2b3f3 [Console]::Out mirror in setup.ps1) still produced an
empty update.log on windows-latest because the powershell.exe child
had no stdio handles at all to write to.
Root cause: subprocess.run on Windows with the default close_fds=True
(Python 3.7+ default) sets bInheritHandles=False on CreateProcess.
Combined with CREATE_NO_WINDOW (added by _windows_hidden_subprocess_
kwargs in non-TTY runs), the child gets:
- no console (CREATE_NO_WINDOW)
- no inherited std handles (bInheritHandles=False)
GetStdHandle in the child returns INVALID_HANDLE_VALUE, so even
[Console]::Out.WriteLine and Write-Output -- not just Write-Host --
write into the void.
Fix: pass stdout=sys.stdout, stderr=sys.stderr (and stdin) when
running the setup script on Windows. With explicit handles, Python's
subprocess sets up PROC_THREAD_ATTRIBUTE_HANDLE_LIST containing the
std handles + bInheritHandles=True, so the child inherits exactly
the three std handles regardless of close_fds=True. CREATE_NO_WINDOW
still applies (no transient console window), but the child can now
write to the inherited stdout file handle, which lands on bash's
`tee logs/update.log` in CI.
A small _stream_for_subprocess helper guards against test harnesses
that swap sys.stdout for a stream without a real fileno (pytest
capsys, in-memory IO buffers, etc) -- those fall back to None so
subprocess uses its default.
Verified locally on PowerShell 7.4.6 / Linux that the explicit
stdout handoff doesn't regress the existing direct-inherit path,
and the marker line "prebuilt up to date and validated" reaches
both the child's stdout and a parent `tee` consumer.
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