## Summary
- run the split stdout/stderr PTY test through the normal shell helper
on every platform
- use a Windows-native command string instead of depending on Python to
emit split streams
- assert CRLF line endings on Windows explicitly
## Why this fixes the flake
The earlier PTY split-output test used a Python one-liner on Windows
while the rest of the file exercised shell-command behavior. That made
the test depend on runner-local Python availability and masked the real
Windows shell output shape. Using a native cmd-compatible command and
asserting the actual CRLF output makes the split stdout/stderr coverage
deterministic on Windows runners.
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