[BUG] Not honoring SHELL variable when bash is not installed

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

when bash is not present commands fails with: Command failed: No suitable shell found. Claude CLI requires a Posix shell environment. Please ensure you have a valid shell installed and the SHELL environment variable set.

even when SHELL is properly set, in that case to /bin/sh which may be a link to dash for debian or ash for alpine.

when embedding /bin/bash to run /bin/sh instead it gives:

! pwd                                                                                                                   
  ⎿  /bin/sh: /home/user/.claude/shell-snapshots/snapshot-bash-1773322226470-3377uk.sh: line 4: shopt: not found
     /tmp

What Should Happen?

honour the SHELL environment variable to generate the snapshots

Error Messages/Logs

Command failed: No suitable shell found. Claude CLI requires a Posix shell environment. Please ensure you have a valid shell installed and the SHELL environment variable set.

Steps to Reproduce

1. Install native claude on Alpine skipping the install script:

docker run --rm -it alpine
# inside the image instance:
apk add -q --no-cache libgcc libstdc++
wget -qO- https://storage.googleapis.com/claude-code-dist-86c565f3-f756-42ad-8dfa-d59b1c096819/claude-code-releases/2.1.74/linux-x64-musl/claude |
  install -o 0 -g 0 -m 755 /dev/stdin /usr/local/bin/claude

1. Setup and run it on any directory:

mkdir ~/.claude
cp ... ~/.claude/.credentials.json # replate it...
cat > ~/.claude.json <<'EOF'
{
  "hasCompletedOnboarding": true,
  "theme": "light",
  "installMethod": "native",
  "autoUpdates": false
}
EOF
# ...
mkdir ~/project
cd $_
export SHELL=/bin/sh
claude

1. Select trust this directory
2. Run a command such as !pwd

Claude Model

None

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.1.74

Platform

Anthropic API

Operating System

Other Linux

Terminal/Shell

Xterm

Additional Information

workaround:

install -o 0 -g 0 -m 755 /dev/stdin /bin/bash <<'EOF'
#!/bin/sh
echo "$(date +%T) $0 $*" >> /tmp/.logs
sed -i -r '/shopt/d' ~/.claude/shell-snapshots/snapshot-bash-*.sh 2> /dev/null || :
exec /bin/sh "$@"
EOF

ideally /tmp/.logs should be empty because if it honour SHELL environment variable there should be no call to other shells.