fix(tools): guard Unix-only imports in terminal package for Windows

[WolffM]

Summary

Fixes OpenHands/OpenHands#12781

• Guard SubprocessTerminal and TmuxTerminal imports in terminal/terminal/__init__.py behind platform.system() != "Windows" so the package loads cleanly on Windows
• Add an explicit raise ImportError guard in subprocess_terminal.py before the Unix-only fcntl/pty/select imports, replacing the opaque ModuleNotFoundError

Fixes the crash where import openhands.tools.terminal immediately fails on Windows with ModuleNotFoundError: No module named 'fcntl' before factory.py can raise its NotImplementedError("Windows is not supported yet").

Context

The import chain was:

openhands.tools.terminal → terminal/__init__.py → subprocess_terminal.py → import fcntl → crash

factory.py already had platform awareness (raises NotImplementedError on Windows), but it never got a chance to run because __init__.py eagerly imported the Unix-only backends at module level.

[WolffM]

tested it against my fork of openhands

[enyst]

Thank you for the PR!

Please let me note that we have another here:

• Windows terminal

and in that line there's a bit of an alternative way to do this, separating Windows a bit better within the codebase.

The fix in your PR is normal but unfortunately, there is more to Windows support than not crashing on imports. That actually poses a problem for us, on how to support Windows, and I admit I heavily prefer a more modular approach if we can.

[WolffM]

Thank you for the PR!

Please let me note that we have another here:

* [Windows terminal](https://github.com/OpenHands/software-agent-sdk/pull/1012/changes#diff-b1eac84c61a55b8e78ac0bf8eb58368d0fb9e1a370d13b9b1973aff5e0551fe4R15)

and in that line there's a bit of an alternative way to do this, separating Windows a bit better within the codebase.

The fix in your PR is normal but unfortunately, there is more to Windows support than not crashing on imports. That actually poses a problem for us, on how to support Windows, and I admit I heavily prefer a more modular approach if we can.

Thanks for the quick reply!

I was thinking this PR could serve as a short-term fix until the Windows terminal backend (#1012) is ready. I don't think it conflicts with that work. Right now openhands serve crashes immediately on Windows with an opaque fcntl import error, this fix lets the package actually load so the existing error handling in factory.py can kick in properly. Not sure how many people are hitting this right now, but it would unblock them.

[neubig]

Hi! I'm going to prioritize getting #1012 in ASAP (maybe test tomorrow), but I can revisit after that.