[rhishi99]

Problem

rtk err, rtk test and rtk summary take a command as one string and run it through a shell. On Windows that shell was hardcoded to cmd /C — in two separate copies of the same helper (cmds/rust/runner.rs, cmds/system/summary.rs). Every PowerShell cmdlet or pipeline handed to them fails:

> rtk summary "Get-ChildItem | Measure-Object"
'Get-ChildItem' is not recognized as an internal or external command

PowerShell is the default shell on Windows, so this is the common case, not an edge case.

Fix

Both copies collapse into one core::shell module which resolves the shell rather than assuming it:

1. RTK_SHELL wins when set — cmd, powershell, pwsh, sh, bash, or any executable name or path.
2. On Windows, if the command's leading word is neither a cmd builtin nor a program on PATH, it is PowerShell syntax → route to pwsh if installed, else powershell.
3. Otherwise the platform default: cmd on Windows, sh elsewhere.

rtk summary "dir /b"                          # cmd.exe
rtk summary "Get-ChildItem | Measure-Object"  # PowerShell
$env:RTK_SHELL = 'pwsh'                       # pin it explicitly

Non-Windows behaviour is unchanged — without RTK_SHELL it is still sh -c, exactly as before.

Why not detect the parent shell

That is the obvious approach and it does not work here:

• Walking parent processes needs Win32 calls this crate forbids (unsafe_code = "deny").
• The environment carries no usable signal — PSModulePath is inherited by cmd children, so its presence proves nothing.
• Parsing cmd.exe's is not recognized as an internal or external command is locale-dependent.

Deciding from the command text needs no parent process, costs one PATH lookup, and is locale-independent. cmd builtins are listed explicitly because no file on PATH backs them, so a PATH lookup alone would misread dir or echo as PowerShell.

Testing

Unit tests in core::shell cover RTK_SHELL precedence, builtin detection, PATH-program detection, the PowerShell fallback, quoted leading words, and the empty-command case. Docs added to docs/guide/getting-started/configuration.md.

Full suite on x86_64-pc-windows-gnu: 2626 passed. cargo fmt --check and cargo clippy --all-targets clean. The single unrelated failure on this toolchain is fixed in #3615.

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[KuSh]

Thanks for working on this, rhishi99. #4125 (merged 2026-09-26) replaced the shell handling in rtk err, test and summary: positional commands now run directly, and a script goes through an explicit --shell, which accepts pwsh and powershell with -Command from a shared src/core/shell.rs. The duplicated cmd /C helpers this PR merges into one are already gone on develop. What develop still lacks is a way to reach PowerShell without --shell, such as an RTK_SHELL default or detection of PowerShell syntax; if you still want that, an issue or a narrow PR on the --shell model would be welcome. If I missed something this PR covers, please comment or reopen.