Claude Code v2.1.41+ sets CLAUDECODE=1 in all child Bash processes and
rejects startup when the variable is present. When codeagent-wrapper
spawns `claude -p` as a subprocess, it inherits this variable and gets
blocked with "cannot be launched inside another Claude Code session".
Add UnsetEnv method to commandRunner interface and strip CLAUDECODE
before spawning the claude backend.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>