fix: prefer PowerShell 7 over legacy Windows PowerShell 5.1

[marius-kilocode]

Kilo Code on Windows keeps selecting Windows PowerShell 5.1 for agent command execution even when PowerShell 7 is installed (#13324). PS 5.1 writes UTF-16LE with a BOM for Out-File/> redirection and has other encoding differences, so agent-driven commands can corrupt files that pwsh would leave intact.

Root cause, from the current selection logic:

• Shell.preferred()/Shell.acceptable() in packages/core/src/shell.ts resolve pwsh only via PATH lookup. When the kilo serve process inherits a PATH without the pwsh directory (common with Store installs whose alias lives under %LOCALAPPDATA%\Microsoft\WindowsApps), detection silently degrades to System32\WindowsPowerShell\v1.0\powershell.exe.
• The extension reads vscode.env.shell but only forwards it to the webview for display; the CLI shell selection never sees it.
• Several execution paths bypass core selection entirely and hardcode legacy PowerShell: Agent Manager setup/run script launchers and the background-process Win32 probes in the CLI.

Plan on this branch:

1. Regression tests (this commit): win32-gated tests in packages/core/test/kilocode/powershell.test.ts assert that with pwsh stripped from PATH, an installed PowerShell 7 still wins over legacy 5.1. They are expected to fail on the Windows CI shard until the fix commit lands.
2. Fix: probe well-known pwsh install locations (%ProgramFiles%\PowerShell\7, %ProgramFiles(x86)%\PowerShell\7, %LOCALAPPDATA%\Microsoft\WindowsApps) after PATH lookup fails, keep explicit shell config as the highest-priority override, and switch the hardcoded call sites to prefer pwsh when present.

Refs #13324

[kilo-code-bot]

Code Review Summary

Status: 1 Issue Found | Recommendation: Address before merge

Overview

Severity	Count
CRITICAL	0
WARNING	1
SUGGESTION	0

Issue Details (click to expand)

WARNING

File	Line	Issue
packages/kilo-vscode/src/util/powershell.ts	23	locations() returns full pwsh.exe paths, but pwshPath() treats them as directories and joins pwsh.exe again, so off-PATH installs are never found

Files Reviewed (12 files)

• .changeset/prefer-powershell-7-on-windows.md - 0 issues
• packages/core/src/kilocode/powershell.ts - 0 issues
• packages/core/src/shell.ts - 0 issues
• packages/core/test/kilocode/powershell.test.ts - 0 issues
• packages/kilo-vscode/src/agent-manager/SetupScriptRunner.ts - 0 issues
• packages/kilo-vscode/src/agent-manager/run/service.ts - 0 issues
• packages/kilo-vscode/src/util/powershell.ts - 1 issue
• packages/kilo-vscode/tests/unit/powershell.test.ts - 0 issues
• packages/kilo-vscode/tests/unit/run-script-service.test.ts - 0 issues
• packages/opencode/src/kilocode/background-process/index.ts - 0 issues
• packages/opencode/src/kilocode/background-process/runner.ts - 0 issues
• packages/opencode/src/kilocode/shell/shell.ts - 0 issues

Fix these issues in Kilo Cloud

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_{Reviewed by grok-4.6 · Input: 148.5K · Output: 17.7K · Cached: 542.6K}

_{Review guidance: REVIEW.md from base branch main}

[WebReflection]

not a big deal, neither a blocker, rather a FYI, nowadays it'd be probe(env).at(0) to avoid "messing" with arrays (because if the length is 0 it would access an undefined index)