fix: support Windows hosts for provider CLI resolution and process termination

[inahus99]

Description

Yoke currently cannot drive Codex or Claude on a Windows host. Provider CLIs installed through npm are reported as "not found on PATH" on every Windows machine, and claude auth status can hang indefinitely instead of timing out. This PR makes the provider process layer work on Windows.

Executable resolution. npm installs CLIs as .CMD/.BAT shims. asyncio.create_subprocess_exec("codex", ...) cannot launch those by bare name, so every readiness check reported the CLI as missing even when it was installed and working. Commands are now resolved through shutil.which, which honours PATHEXT and finds the shim.

Process termination. Killing only the wrapper PID leaves the npm shim's child tree running. Windows now terminates via taskkill /T /F; POSIX signals the child's process group. claude auth status is additionally bounded by a timeout so a stalled CLI reports a repair hint rather than blocking the caller forever.

Path serialization. Paths sent to provider APIs are serialized with as_posix(), so Windows drive paths round-trip through providers that expect POSIX separators.

The new yoke.process module holds this logic in one place; it depends only on the standard library and adds no new requirements.

Relationship to #3 and #5

This PR overlaps with two of @Adityakk9031's open PRs. That overlap was not deliberate — I found both only after the work was written — and I want to be explicit about it rather than quietly talk over them.

#5 (scriptPath POSIX serialization) — this branch contains the identical one-line change. I tried removing it to defer to #5, and tests/test_workflows.py::test_file_workflow_requires_native_workflow_feature fails on Windows without it, so it is a hard prerequisite for a green Windows suite rather than something I can drop. I'm happy to rebase this branch on top of #5 and drop the line the moment #5 lands — that ordering is better and the credit for the fix is theirs.

#3 (WinError 87 in process_is_alive) — same underlying bug, different fix. #3 adds except OSError: return False to the existing helper. This branch instead moves process_is_alive into yoke.process and, on Windows, queries the process through OpenProcess/GetExitCodeProcess rather than calling os.kill at all, so WinError 87 cannot arise in the first place. If maintainers would rather land the smaller, more targeted #3 first, I'll rebase on it.

I have no preference about ordering and would rather both of their PRs merge first than have this one supersede them. Ordering is entirely the maintainers' call.

CI

Yoke's CI ran on ubuntu-latest only, so code whose whole purpose is Windows behaviour had no Windows coverage. This adds a windows-latest leg across Python 3.11/3.12/3.13 with fail-fast: false. That matrix is the only thing that will exercise the new POSIX process-group test on Linux and the shim-resolution tests on Windows.

Testing

• 507 passed, 1 skipped locally on Windows 11 / Python 3.13 (1 skipped is the POSIX-only process-group test, which runs on the Ubuntu legs).
• ruff check . clean.
• New tests cover shim resolution via PATHEXT, the readiness timeout path, working-directory shadowing, POSIX descendant termination, and the self-kill guard.

Two behaviours worth reviewer attention, both covered by tests:

• A bare command name now always resolves through PATH. Previously any command naming an existing file was treated as a path, so a file called codex in the working directory could shadow the real executable while Yoke operated on an untrusted checkout. Commands written as paths are returned verbatim rather than normalized, because str(Path("./codex")) strips the ./ and turns an explicit relative path back into a PATH lookup.
• The POSIX tree kill skips the group kill when the target shares the caller's process group, so a caller can never signal itself. Only children started with start_new_session=True lead their own group.

Note on release sequencing

CodeAlmanac's Windows support depends on this landing and being published as 0.1.8 — its pin is almanac-yoke[claude]>=0.1.8. The version bump is included here, but cutting the tag and release is obviously a maintainer action. If this merges, a 0.1.8 release would unblock the CodeAlmanac side; happy to open that PR whenever it's useful.

---

^{Need help on this PR? Tag @codesmith-bot with what you need. Autofix is disabled.}

[Adityakk9031]

Hi @inahus99, thanks for your detailed note and for highlighting the overlap!

We have updated PR #3 and PR #5 to include the complete set of Windows support enhancements:

• PR fix: support Windows executable resolution, process-tree termination, and process_is_alive Win32 API #3 now includes the yoke.process module with Win32 API process liveness checks (OpenProcess / GetExitCodeProcess), taskkill /T /F process tree termination, npm .CMD shim resolution via shutil.which, and bounded readiness execution.
• PR fix: serialize filesystem paths with POSIX separators for provider APIs and add Windows CI #5 now includes comprehensive .as_posix() path serialization across all provider APIs (claude.py, codex_sdk.py, codex_app_server.py, codex_agents.py, models.py) as well as the windows-latest GitHub Actions CI matrix leg.

Both PRs have been updated, pushed, and are green and ready for maintainer review!