Yaowei Zheng
3.3 KiB
Windows: the package bundles its own bash, so the Agent's shell no longer depends on the machine
penguin-win32-x64.zip now ships MinGit under git/, and exec_command uses it when the machine has no Git for Windows of its own.
Why
The Windows shell was whatever happened to be installed: bash if the user had Git for Windows, otherwise PowerShell. That made the same Agent running the same Skill behave differently on two Windows machines, and the degradation was silent — a Skill written for a POSIX shell does not fail loudly under PowerShell, it fails strangely. The sharpest case: curl -fsSL <url> under Windows PowerShell 5.1 resolves the built-in curl → Invoke-WebRequest alias and returns a cmdlet parameter-binding error, which a model recovers from far less easily than "command not found".
What is bundled
MinGit's usr/bin/sh.exe is GNU bash — the minimal Git for Windows build installs bash under the name sh. So the bundle costs 37MB compressed (~91MB installed) for a real bash, roughly sixty core utilities, and git.exe, rather than the ~350MB extracted that full PortableGit would have needed for complete parity.
No PATH plumbing is involved. MinGit's etc/profile defaults to MSYS2_PATH_TYPE=inherit, so a login shell (-lc, unchanged) yields /mingw64/bin:/usr/local/bin:/usr/bin:/bin:<inherited Windows PATH> — bundled tools and git first, the Windows PATH still behind them. That is why MinGit carrying no curl or tar does not matter: System32's curl.exe and tar.exe keep resolving, and inside bash they are the real binaries rather than PowerShell aliases.
Resolution order
PENGUIN_SHELL → bash on PATH → bundled → pwsh → powershell.
The bundle sits deliberately after the PATH probe: a user's own Git for Windows carries the complete MSYS userland (curl, tar, less, perl …) while MinGit carries about sixty tools, so when both exist theirs is the better shell. The bundle is the floor, not the preference. pwsh / powershell stay reachable for npm installs, which bundle nothing. The resolved shell is reported to the model as bash, since that is what it is and what the Skill ecosystem targets.
The installer treats git/ like the other payload directories — replaced on upgrade, never touching the data directory — and the launcher shims advertise the path as PENGUIN_BUNDLED_SHELL.
Licensing
MinGit is GPLv2, so a new root THIRD-PARTY-NOTICES.md records both bundled components — the Node runtime and MinGit — with where each one's license text sits inside the bundle and where its corresponding source lives. The Git for Windows release is pinned to one exact tag so the notice names a single version, and the bundled bytes are the unmodified published asset.
Cost, stated plainly
The Windows download roughly doubles (~65MB → ~100MB) and the install grows about 91MB; Expand-Archive on PowerShell 5.1 has 368 more files to unpack, so a fresh install is noticeably slower. The bundle also means a hybrid environment — MSYS coreutils beside native node and git — not a POSIX one, so MSYS path translation remains a thing to watch. MSYS_NO_PATHCONV / MSYS2_ARG_CONV_EXCL are deliberately left unset: matching real Git Bash semantics is the least surprising default, and diverging would make the bundled shell behave unlike the PATH one.