[Bug]: ERROR: Windows stdio in console mode does not support writing non-UTF-8 byte sequence

[Alexx999]

Bug Description

On Windows REPL gets hard failure the moment a subprocess emits any non-UTF-8 byte — even though the command itself succeeded. You get a message that says:

ERROR: Windows stdio in console mode does not support writing non-UTF-8 byte sequences

Steps to Reproduce

1. Start forge on Windows.
2. From the agent, have it invoke the shell tool with a command whose output contains non-UTF-8 bytes. Any of these work:

   • powershell -NoProfile -Command "Write-Host ([char]0x91 + 'hi' + [char]0x92)"

     (Windows-1252 curly quotes — invalid UTF-8.)
   • Read a file containing a Windows-1252 character:

     powershell -NoProfile -Command "Get-Content 'some-file-with-smart-quotes.txt'"

   • Run any binary that prints UTF-16 or OEM-codepage bytes.
3. The tool call fails with the message above

Expected Behavior

A subprocess that prints non-UTF-8 bytes must not break the shell tool.

Actual Behavior

A subprocess that prints non-UTF-8 bytes breaks the shell tool.

Forge Version

2.11.3

Operating System & Version

Win11

AI Provider

Anthropic

Model

opus-4-7

Installation Method

Other

Configuration