[BUG] Windows: sandbox bash ignores CLAUDE_CODE_SHELL and sandbox.enabled: false (v2.1.59)

Bug Description

On native Windows 11, Claude Code v2.1.59 uses a bundled sandbox bash (/usr/bin/bash.exe, linux-gnu build) regardless of configuration. Both CLAUDE_CODE_SHELL and sandbox.enabled: false are ignored.

The sandbox bash lacks standard Unix utilities (ls, grep, head, tail, awk, sed, cat, find, which), making shell commands that pipe through these utilities fail. Core tools like cargo and git work since they are Windows executables on PATH.

Steps to Reproduce

1. On native Windows 11 (not WSL), install Claude Code v2.1.59
2. Set CLAUDE_CODE_SHELL to Git for Windows bash:

• Via setx CLAUDE_CODE_SHELL "D:\Program Files\Git\usr\bin\bash.exe" (persistent user env var), and/or
• Via settings.json:

``json
{
"env": {
"CLAUDE_CODE_SHELL": "D:\\Program Files\\Git\\usr\\bin\\bash.exe"
},
"sandbox": {
"enabled": false
}
}
``

1. Restart Claude Code
2. Run any bash command — observe it uses /usr/bin/bash (sandbox) not Git bash

Evidence

$ echo "SHELL=$SHELL"
SHELL=/usr/bin/bash.exe

$ echo "bash=$0"
bash=/usr/bin/bash

$ echo "version=$BASH_VERSION"
version=5.2.37(1)-release       # linux-gnu build, not Git for Windows

$ echo "CLAUDE_CODE_SHELL=$CLAUDE_CODE_SHELL"
CLAUDE_CODE_SHELL=D:\Program Files\Git\usr\bin\bash.exe   # env var IS set, just ignored

$ type ls
/usr/bin/bash: line 1: type: ls: not found   # no Unix utilities available

Expected Behavior

• sandbox.enabled: false should disable the sandbox bash entirely on Windows
• CLAUDE_CODE_SHELL should select which bash binary is used
• On native Windows (where sandbox docs state "Native Windows support is planned"), the sandbox should not be active at all

Environment

• OS: Windows 11 Pro 10.0.26200
• Claude Code: v2.1.59
• Shell: Git for Windows bash at D:\Program Files\Git\usr\bin\bash.exe (v2.53.0)
• Platform: Native Windows (not WSL)