- Ensure traceback is stored properly for error results.
- Restart the stats recorder in forked children via
os.register_at_fork. Previously the writer thread existed only in the process that calledenable_stats(), so a consumer w/worker_type='process'(or a preforking web server that loads the app before forking) buffered task events in its workers but never wrote them, and the dashboard showed tasks stuck on "enqueued".
