The --kv-disk-dir parse loop used `for _i, _t in ...`, making `_t` a local
in main() and shadowing the module-level `import threading as _t`, so the
later `_t.Thread(...)` raised UnboundLocalError and crash-looped both
engines. Renamed the loop var to `_tok`.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>