Cap subagent parallelism in CLAUDE.md before a fan-out run quietly bills five figures

CloudZero·medium signal

Parallel Claude Code subagents each run a full independent context window, so five in parallel burn roughly 5x the tokens of one — and reported real incidents include a 23-subagent code-quality job that consumed $47,000 over three days. The mitigation is to set an explicit parallelism cap in CLAUDE.md and never leave subagent chains running unattended. This is the unglamorous governance counterpart to 'just fan out more agents,' and it belongs in every team's project config.