Windows branch shell.rs frequently and incorrectly handles pwsh, causing command execution failures.

What version of Codex is running?

0.34.0

Which model were you using?

GPT-5-high

What platform is your computer?

Microsoft Windows 10 10.0.19045 x64-based PC

What steps can reproduce the bug?

1. Run a command containing quotes or Windows paths on a Windows environment.

1. The program incorrectly triggers Unix commands or fails due to escaping issues.

What is the expected behavior?

• Prioritize pwsh in the Windows branch.
• If pwsh fails, fallback should be Windows PowerShell, not bash.
• Optionally perform a self-check at program startup:
• If Unix tools are required, inform the user clearly to install them instead of silently failing.
• Avoid repeated failures (currently a single execution may fail 5–6 times), as this makes logs noisy and user interaction confusing.
• Use ScriptBlock execution for pwsh commands to ensure proper escaping.

What do you see instead?

<img width="727" height="439" alt="Image" src="https://github.com/user-attachments/assets/c1b1d7ae-e47a-48c8-b1c4-c861f1a6ae05" />

<img width="973" height="102" alt="Image" src="https://github.com/user-attachments/assets/b9219a4f-7a5f-4874-b21b-59273074c5aa" />

<img width="1085" height="174" alt="Image" src="https://github.com/user-attachments/assets/fb54877a-1ed9-484c-bd68-9c7a3b3915d2" />

<img width="1051" height="266" alt="Image" src="https://github.com/user-attachments/assets/b2de9762-0510-415b-8e21-95e39a15d982" />

Additional information

I previously submitted a PR (#3253
) that attempted to improve this behavior. While the implementation might not have been perfect, in practice it significantly reduced command execution errors and ensured that pwsh was consistently prioritized.