(feat): Default Windows terminals to PowerShell instead of cmd.exe

[Justmalhar]

What

New terminals on Windows now launch Windows PowerShell instead of cmd.exe.

Why

resolveDefaultTerminalShell (the single source of truth for a new terminal's shell — terminal-manager.ts never passes an explicit shell) read env.ComSpec on win32. Windows always points ComSpec at …\System32\cmd.exe, so every new terminal opened cmd.

How

The win32 branch now returns …\System32\WindowsPowerShell\v1.0\powershell.exe, built from %SystemRoot% (honoring a relocated Windows install) with a C:\Windows fallback. Windows PowerShell 5.1 ships in System32 on every supported Windows, so the path is always valid and the resolver stays pure/synchronous (no PATH probing).

Untouched and verified safe:

• resolveTerminalSpawnCommand (routes agent .cmd/.bat profiles like claude through cmd.exe /c) — unchanged.
• Shell integration only ever existed for zsh, so there's no Windows integration to lose.

Tests

• Rewrote the contract unit test to expect PowerShell and assert ComSpec no longer pulls it back to cmd.
• Added a test for a relocated %SystemRoot%.

Note: this is a hardcoded switch with no opt-out. If a per-user shell knob is wanted later, the clean spot is a PASEO_TERMINAL_SHELL check at the top of the same win32 branch.

[greptile-apps]

Greptile Summary

This PR changes the default terminal shell on Windows from cmd.exe (previously derived via ComSpec) to Windows PowerShell 5.1 at %SystemRoot%\System32\WindowsPowerShell\v1.0\powershell.exe.

• terminal.ts: The win32 branch of resolveDefaultTerminalShell now builds the PowerShell path from env.SystemRoot ?? env.SYSTEMROOT ?? "C:\\Windows", completely ignoring ComSpec. The resolver remains pure and synchronous.
• terminal.test.ts: The contract test is rewritten to assert PowerShell is returned and ComSpec no longer influences the result; a second new test covers a relocated %SystemRoot% (e.g., D:\Windows).

Confidence Score: 5/5

Safe to merge — the change is a targeted, two-line swap with well-exercised tests and no impact on agent command routing.

The implementation correctly reads SystemRoot/SYSTEMROOT from the environment, falls back to C:\Windows, and constructs a path that is always valid on supported Windows versions. The old ComSpec logic is fully removed with no dead code. Tests cover the empty-env case, the ComSpec-is-present case, and a relocated %SystemRoot%. No existing behavior on non-Windows platforms is touched.

No files require special attention.

Important Files Changed

Filename	Overview
packages/server/src/terminal/terminal.ts	Replaces ComSpec lookup with a hardcoded PowerShell path built from %SystemRoot%; change is minimal, correct, and pure.
packages/server/src/terminal/terminal.test.ts	Test updated to assert PowerShell is returned and ComSpec is ignored; new test covers relocated %SystemRoot%. Both tests exercise the module interface directly with no banned patterns.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[resolveDefaultTerminalShell called] --> B{platform === 'win32'?}
    B -- No --> C[return env.SHELL or /bin/sh]
    B -- Yes --> D[read env.SystemRoot or env.SYSTEMROOT]
    D --> E{env var present?}
    E -- Yes --> F[systemRoot = env value]
    E -- No --> G[systemRoot = 'C:\\Windows']
    F --> H[return systemRoot + '\\System32\\WindowsPowerShell\\v1.0\\powershell.exe']
    G --> H

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%%{init: {'theme': 'base', 'themeVariables': {"darkMode": true, "background": "#0d1117", "primaryColor": "#21262d", "primaryTextColor": "#e6edf3", "primaryBorderColor": "#8b949e", "lineColor": "#8b949e", "textColor": "#e6edf3", "edgeLabelBackground": "#161b22", "actorBkg": "#21262d", "actorBorder": "#8b949e", "actorTextColor": "#e6edf3", "actorLineColor": "#8b949e", "signalColor": "#8b949e", "signalTextColor": "#e6edf3", "noteBkgColor": "#373320", "noteBorderColor": "#d4a72c", "noteTextColor": "#f0e6c0", "labelBoxBkgColor": "#21262d", "labelBoxBorderColor": "#8b949e", "labelTextColor": "#e6edf3", "loopTextColor": "#e6edf3", "activationBkgColor": "#30363d", "activationBorderColor": "#8b949e"}}}%%
flowchart TD
    A[resolveDefaultTerminalShell called] --> B{platform === 'win32'?}
    B -- No --> C[return env.SHELL or /bin/sh]
    B -- Yes --> D[read env.SystemRoot or env.SYSTEMROOT]
    D --> E{env var present?}
    E -- Yes --> F[systemRoot = env value]
    E -- No --> G[systemRoot = 'C:\\Windows']
    F --> H[return systemRoot + '\\System32\\WindowsPowerShell\\v1.0\\powershell.exe']
    G --> H

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