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Windows setup-runner shell

On native Windows, Orca writes the orca.yaml setup script (and the issue command) to a generated runner file and types a launch command into a terminal. The runner is a .cmd batch file by default, exactly as it has been since setup hooks shipped.

A script opts into bash by starting with a #! interpreter line:

scripts:
  setup: |
    #!/usr/bin/env bash
    [ -f .env ] || cp .env.example .env
    pnpm install

Without that line the script keeps running under cmd.exe:

scripts:
  setup: |
    copy .env.example .env
    xcopy /E assets dist

Why the script declares it, not the terminal preference

terminalWindowsShell says which shell interactive terminals open in. It says nothing about the language a project's setup script is written in. Deriving the runner from it had two consequences:

Windows users with batch-syntax setup scripts silently switched to bash on upgrade, so copy, xcopy, set VAR=value, and if errorlevel 1 stopped working.
Two people on the same repo got different interpreters for the same orca.yaml, so no project could write a setup script that worked for all of its Windows contributors.

A #! line is per-project, explicit, and identical for everyone who checks the repo out.

The same rule applies to the per-user setup command in Settings → repository hooks (repo.hookSettings.scripts.setup): it is merged into the same script that reaches the runner, so a POSIX one-liner stored there needs its own #! line to run under bash on Windows.

What the `#!` line does and does not select

The generated runner is always executed by bash (bash <runner>; Git Bash on native Windows), on every platform. The #! line therefore does two things:

It declares the script is written for a POSIX shell, which is what selects the bash runner.
Its option flags are replayed with set, so #!/usr/bin/env -S bash -euo pipefail really does get pipefail. Without that replay the flags would be silently dropped, because bash <runner> never parses the interpreter line. Only the flags set itself accepts ([--abefhkmnptuvxBCHP] [-o option]) are replayed; invocation-only ones such as -l are dropped, because set -l exits 2 and would abort the runner before its first line.

The interpreter name itself is not honored beyond "is this a POSIX shell": #!/bin/sh and #!/bin/zsh scripts run under bash, exactly as they already did on macOS and Linux.

Requirements for the bash runner

A #! line only takes effect when Orca can actually launch bash from the configured terminal — the terminal shell must resolve to Git Bash (resolveWindowsGitBashShellPath). The generated runner uses MSYS /c/... paths, which Cygwin and the WSL shim do not accept, and the launch command is typed into whatever shell the terminal opened with.

When bash is not available (a PowerShell/cmd terminal, or an SSH-to-Windows host, which always uses the remote's .cmd runner) the #! script is not executed under cmd. The generated .cmd runner prints why and exits 1, because running the interpreter-agnostic prefix of a bash script (pnpm install, git submodule update) and only failing at the first bash-only line leaves a half-set-up worktree that looks finished.

Launching a `.cmd` runner from a Git Bash terminal

The runner format and the shell that types the launch command are independent: a Git Bash terminal with a batch-syntax setup script gets a .cmd runner launched from a bash pane. cmd.exe /c "C:\..." cannot be used there — MSYS rewrites the bare /c switch into a drive path, so cmd opens interactively and the runner never executes (issue #6896). Those launches reuse the PowerShell ProcessStartInfo launcher (buildWindowsCmdRunnerDelayedLaunchCommand), which carries the switch and the runner path outside the command line. WorktreeSetupLaunch.shell therefore describes the launching pane; the runner file's .cmd/.sh extension describes the format.

The wait-for-setup gate follows the same split. The pane types the gate and already quoted the agent startup command for itself, so a .cmd runner launched from a Git Bash pane still gets the bash gate — PowerShell's Invoke-Expression cannot parse POSIX '\'' escaping. The gate wraps the same ProcessStartInfo launcher, so the batch runner is never handed to bash.

WSL worktrees and non-Windows platforms are unaffected: they always use the bash runner. SSH hosts choose their runner from the remote path format, never from local Windows preferences.

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