Fix Windows compatibility: subprocess preexec_fn is POSIX-only

[Lê Anh Duy (Le-Anh-Duy)]

subprocess.Popen(preexec_fn=..., start_new_session=True) raised "preexec_fn is not supported on Windows platforms" for every LLM call and test-runner invocation, causing /cmind.encode and friends to fail outright on Windows.

Branch on platform: POSIX keeps start_new_session + preexec_fn (killpg-based tree kill); Windows uses CREATE_NEW_PROCESS_GROUP and a new _kill_process_tree() helper that shells out to taskkill /T /F to reap the process tree instead.

Verified end-to-end: reinstalled the patched package as the local cmind-cli tool and ran a full /cmind.encode against an external repo on Windows; it now completes successfully (previously failed on every LLM call).

[Lê Anh Duy (Le-Anh-Duy)]

@microsoft-github-policy-service agree

[Copilot]

Pull request overview

Fixes Windows incompatibility caused by using POSIX-only subprocess.Popen(preexec_fn=...) by branching process-spawn and process-tree cleanup behavior by platform.

Changes:

• Add a platform-aware process-tree termination helper and use it for timeout/exception cleanup.
• Make Popen invocation platform-specific: POSIX uses start_new_session + preexec_fn, Windows uses CREATE_NEW_PROCESS_GROUP.
• Expand .gitignore entries for CoderMind-managed local directories/files.

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 2 comments.

File	Description
CoderMind/scripts/common/llm_client.py	Adds Windows-safe process spawning and cross-platform process-tree kill helper for LLM CLI invocations.
CoderMind/scripts/code_gen/test_runner.py	Reuses the shared process spawning/kill logic for pytest/project test execution with Windows support.
.gitignore	Adds ignore rules for CoderMind-managed local artifacts and config, with an exception for config.toml.

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[Qingtao Li (QingtaoLi1)]

Lê Anh Duy (@Le-Anh-Duy) Thanks for your fix patch! CoderMind has not been officially tested on Windows platform. I tested your patch and it does fix the subprocess compatibility problem. However, the /cmind.encode command still fails with input errors on my Windows device. Does the /cmind.encode command run well at your side?

[Lê Anh Duy (Le-Anh-Duy)]

Hello, thanks for reviewing, it works fine on my machine, i'm investigating the bug. As claude code suggested, it might be encoding issues in CoderMind/scripts/update_graphs.py and llm_client.py:417-430, where the program is trying to print special character like "→", which window console might used its locale encoding system instead of utf-8, and cause the issues. Can you try to test the patch on a smaller project with no special character? Vào Thứ 6, 10 thg 7, 2026 vào lúc 11:24 Qingtao Li < ***@***.***> đã viết:

…

*QingtaoLi1* left a comment (microsoft/RPG-ZeroRepo#85) <#85 (comment)> @Le-Anh-Duy <https://github.com/Le-Anh-Duy> Thanks for your fix patch! CoderMind has not been officially tested on Windows platform. I tested your patch and it does fix the subprocess compatibility problem. However, the /cmind.encode command still fails with input errors on my Windows device. Does the /cmind.encode command run well at your side? — Reply to this email directly, view it on GitHub <#85?email_source=notifications&email_token=BES56B6RKU7ITRAYPWPSEX35EBVYVA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTIOJTGE4TOMJUG4YKM4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJLDGN5XXIZLSL5RWY2LDNM#issuecomment-4931971470>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/BES56BZFEHCF7I4UZ7LNWTT5EBVYVAVCNFSNUABGKJSXA33TNF2G64TZHMYTCMBUGQZTKNJTHE5US43TOVSTWNBYGQYDCMZUGIYDNILWAI> . You are receiving this because you were mentioned.Message ID: ***@***.***>

[Lê Anh Duy (Le-Anh-Duy)]

Hi Qingtao, Following up on your question about whether /cmind.encode runs cleanly on my Windows machine — I dug into it and found a real, reproducible Windows bug. I've opened a pull request with the fix: https://github.com/Le-Anh-Duy/RPG-ZeroRepo/tree/fix/windows-utf8-io What I found: cmind script update_graphs.py status (the command behind the SessionStart/post-commit hooks) crashes on Windows with: UnicodeEncodeError: 'charmap' codec can't encode character '→' in position ... Root cause: on Windows, a script's stdout is almost never a real console (it's piped by cmind script, captured by a hook, etc.), so CPython falls back to locale.getpreferredencoding() for stdio instead of UTF-8 — a legacy code page (cp1252/cp936/...) on most Windows installs. update_graphs.py's status output unconditionally prints an MCP-tools guidance line containing "→" (functional areas → groups → features) whenever the RPG is readable, so this isn't a rare edge case — it fires on the normal "status looks fine" path. Why I didn't catch this myself before you flagged it: the hook is deliberately written to fail silently — cmind script update_graphs.py status 2>/dev/null || echo '[CoderMind] RPG status unavailable' — so instead of a visible crash, all I ever saw was that one bland fallback line. It's easy to read past that as "just a status message" rather than "this just crashed." I confirmed it had in fact been crashing on every session for me too, from the very start — I'd just never noticed, because it degrades gracefully instead of blocking anything. What's still unconfirmed: whether this exact code path is what broke /cmind.encode itself for you. run_encode.py / check_encode.py's own print(json.dumps(...)) calls are ASCII-safe by default, so they shouldn't hit this — which is also consistent with encode always working fine on my end. If some other print()/log call deeper in the encode pipeline emitted a non-ASCII character, it would crash the same way, just somewhere else. If you still have it, could you send me the exact traceback/error text from your /cmind.encode failure? That will tell us for sure whether it's the same bug or a second one to fix. Thanks again for pushing on this — happy to iterate further once I hear back on the traceback. Vào Thứ 6, 10 thg 7, 2026 vào lúc 11:24 Qingtao Li < ***@***.***> đã viết:

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*QingtaoLi1* left a comment (microsoft/RPG-ZeroRepo#85) <#85 (comment)> @Le-Anh-Duy <https://github.com/Le-Anh-Duy> Thanks for your fix patch! CoderMind has not been officially tested on Windows platform. I tested your patch and it does fix the subprocess compatibility problem. However, the /cmind.encode command still fails with input errors on my Windows device. Does the /cmind.encode command run well at your side? — Reply to this email directly, view it on GitHub <#85?email_source=notifications&email_token=BES56B6RKU7ITRAYPWPSEX35EBVYVA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTIOJTGE4TOMJUG4YKM4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJLDGN5XXIZLSL5RWY2LDNM#issuecomment-4931971470>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/BES56BZFEHCF7I4UZ7LNWTT5EBVYVAVCNFSNUABGKJSXA33TNF2G64TZHMYTCMBUGQZTKNJTHE5US43TOVSTWNBYGQYDCMZUGIYDNILWAI> . You are receiving this because you were mentioned.Message ID: ***@***.***>

[Copilot]

Pull request overview

Copilot reviewed 2 out of 3 changed files in this pull request and generated 2 comments.