Every pool thread runs the worker at once with the same states, so a mut state in a worker was a
race nothing reported. check_worker_ref refuses a worker whose leading states include a mut one;
threads.ludic's total moves into the words the worker is handed, under the mutex. The seeds are
regenerated (ludic-dev reseed). ludic-dev test 305 passed, selfhost-test 33 passed.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
