forked from username/flaskpaste
get_pow_secret() generated a random secret per process, so challenges signed by worker A failed verification on worker B (~90% failure rate with 2 workers). Persist a file-backed secret to data/.pow_secret using O_EXCL for atomic creation. FLASKPASTE_POW_SECRET env var still takes priority when configured. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>