--break-system-packages was added in pip 23 (Debian Bookworm). Ubuntu 22.04 ships pip 22 which rejects the flag with exit code 2. Switch to the PIP_BREAK_SYSTEM_PACKAGES env var instead: recognized by pip>=23, silently ignored by pip<23 where PEP 668 is not enforced anyway. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>