[BUG] Windows terminal fallback incorrectly defaults to PowerShell 5.1 (Legacy) ignoring PS7 profile, causing UTF-8 encoding issues #11958

Problem (one or two sentences)

On Windows, Roo Code's background terminal execution (ExecaTerminalProcess) incorrectly falls back to legacy PowerShell 5.1 instead of the user's configured PowerShell 7 profile, causing severe UTF-8 encoding issues (mojibake).

Context (who is affected and when)

This affects Windows users who have explicitly set PowerShell 7 (pwsh.exe) as their default VS Code terminal profile, particularly when executing commands that output non-ASCII characters (e.g., Chinese) during agent tasks.

Reproduction steps

1. On Windows, install PowerShell 7 and set it as the default VS Code terminal profile.
2. Ensure Roo Code's "Disable Terminal Shell Integration" is enabled (this is the default state).
3. Ask Roo Code to run a command that outputs Chinese or other non-ASCII characters (e.g., echo "你好").

Expected result

Roo Code should correctly parse the VS Code terminal settings, use pwsh.exe (PowerShell 7) which natively supports UTF-8, and display the characters correctly without encoding issues.

Actual result

Roo Code incorrectly falls back to powershell.exe (PowerShell 5.1). Since it runs as a non-interactive subprocess, it ignores user $PROFILE settings (like chcp 65001) and defaults to the local system codepage (e.g., GBK), resulting in garbled text output.

Variations tried (optional)

I investigated the source code with my coding agent and found the exact root causes:

Flawed Shell Detection: In src/utils/shell.ts, getWindowsShellFromVSCode() aggressively falls back to SHELL_PATHS.POWERSHELL_LEGACY if the profile name includes "powershell" but lacks an explicit path or source === "PowerShell".
Profile Parsing Bug: In src/integrations/terminal/TerminalProcess.ts, the configuration is read incorrectly using vscode.workspace.getConfiguration("terminal.integrated.defaultProfile").get("windows"). This often returns null, forcing the legacy fallback.

(Note: I have already figured out how to fix these logic flaws and I would love to submit a PR for this if the team agrees with the findings!)

App Version

v3.51.1

API Provider (optional)

Unbound

Model Used (optional)

N/A

Roo Code Task Links (optional)

No response

Relevant logs or errors (optional)