Your Script Called bash. Windows Gave It WSL, Not Git Bash.

Your build script shells out to bash. You test the command by hand and it is correct. From inside the script the same word runs a different shell, against a different filesystem, under a different kernel. Nothing errors. The output is just wrong. where.exe bash on a normal dev box returns three entries - Git for Windows at usr/bin/bash.exe, C:\Windows\System32\bash.exe which is the WSL launcher, and a WindowsApps stub. Git is first, so PATH order is not the problem. That is exactly why it looks fine when you check it. Two resolvers disagree. Your shell asks PATH, and PATH says Git. A script does not go through your shell - it calls CreateProcess with a bare name, and CreateProcess searches the Windows system directory before it touches PATH. System32 holds the WSL launcher, so the script gets WSL regardless of PATH. Both answers out of one process: python -c "import shutil,subprocess; print('lookup :', shutil.which('bash')); print('spawned:', subprocess.run(['bash','-c','uname -s'],capture_output=True,text=True).stdout.strip())" lookup : C:\Program Files\Git\usr\bin\bash.EXE spawned: Linux The fix is to never spawn a bare interpreter name from a script. Resolve it to an absolute path first, derived from something you already trust on PATH: import shutil, subprocess from pathlib import Path git = shutil.which("git") bash = next(p / "usr" / "bin" / "bash.exe" for p in Path(git).parents if (p / "usr" / "bin" / "bash.exe").exists()) subprocess.run([str(bash), "-c", "uname -s"]) That survives a machine where Git sits on another drive, and it cannot be hijacked by whatever Windows ships in System32 next. This one is expensive with coding agents. The agent runs a command, gets plausible output from the wrong shell and the wrong filesystem, and builds its next three steps on it. No error appears anywhere in the transcript. Verified on Windows 11 26300, Git for Windows (MINGW64), WSL bash at C:\Windows\System32\bash.exe, Python 3.11. Free starter kit - the CLAUDE.md rules that pin interpreters by absolute path: https://guzmancer0.gumroad.com/l/cco-... CHAPTERS 00:00 Typed it works, spawned it does not 00:16 where.exe bash returns three answers 00:40 MINGW64 by hand, Linux from a script 01:05 CreateProcess searches System32 before PATH 01:36 The fix - resolve Git Bash from git 01:59 Why this wrecks coding agents This channel covers Windows-native agentic coding - the failure modes the macOS tutorials never reach. Subscribe if you build on Windows and are tired of being told to just use WSL. #windows #python #wsl