Windows: bash tool cannot correctly handle cmd.exe GBK output #26882

Bug Report: Windows cmd.exe GBK output displayed as garbled text in bash tool

Bug Description:
When executing Windows native commands (via cmd /c) or system utilities like ipconfig in OpenCode's bash tool on Windows, Chinese characters are displayed as garbled text (mojibake) instead of proper Chinese text.

Steps to Reproduce:

1. Open OpenCode on Windows 11
2. Execute the following command in the bash tool:

   cmd /c "echo Windows IP 配置"

3. Observe the output shows garbled characters instead of proper Chinese text

Expected Behavior:
Chinese characters should be displayed correctly.

Actual Behavior:
Chinese characters are displayed as garbled text (mojibake), indicating encoding mismatch.

Technical Details:

The same command works correctly when executed directly in pwsh 7.6.1 terminal, but fails in OpenCode's bash tool:

Raw byte analysis confirms ipconfig outputs GBK (CP936) encoding, which is standard for Windows system commands.

Root Cause:
OpenCode's bash tool captures cmd.exe output as raw bytes but processes them with incorrect encoding assumption (expecting UTF-8 instead of detecting GBK). PowerShell 7 correctly uses UTF-8 internally, but the OpenCode rendering layer fails to transcode the GBK output from native Windows commands.

Environment:

• OpenCode: 1.14.48
• Windows: 11
• PowerShell: 7.6.1
• Shell: PowerShell 7 (confirmed via $PSVersionTable.PSVersion)

Additional Context:

• PowerShell native commands output correctly (e.g., Get-NetIPAddress)
• Only Windows native commands (.exe files like ipconfig.exe, cmd.exe) have this issue
• The problem occurs even when PowerShell 7's encoding is set to UTF-8
• File redirection with GBK decoding works: [System.Text.Encoding]::GetEncoding(936).GetString([System.IO.File]::ReadAllBytes("file")) correctly displays Chinese

Suggested Fix:
Implement encoding detection or transcoding for Windows native command output in the bash tool, or add a configuration option to specify the console output encoding (GBK/CP936 for Windows).