- __init__.py: _stop_background_work() detaches the monitor's callbacks,
stops the monitor, closes the preview worker and shuts the prompt
cleanup thread down against one 10 s deadline, once. It runs from
atexit (ComfyUI never runs aiohttp's cleanup hooks), from on_cleanup
where a host runs it, and from the tests' package unload; it removes
its own atexit callback. Registered after the history hook, so at exit
it runs before the history dispose.
- AutoThumbnailer.close/close_auto_thumbnails take a timeout and return
whether the worker ended.
- Tests: teardown result, once-only, on_cleanup, atexit order, a failing
step or a second Ctrl+C never skipping the tracker, one shared
deadline, three repeated loads leaving no thread, and a child process
that exits normally with the image worker alive.
