A finished 12-minute humaneval bench died at the save line: some scorer detail carried a non-JSON object (Ellipsis) and report.save's json.dumps had no default. Every dumps on the save path now stringifies exotic objects instead of killing the run; verified by replaying the exact crashed checkpoint end-to-end (pass 82.3%, 15s, no crash). Co-Authored-By: Claude <noreply@anthropic.com>