Suggestion:
Docs say "When the generator script is running (either with cron or using "Run in background" feature), you will see it's progress state on "Crawling" page. There you will also find the link to stop the script, which is very useful for big sites because you don't have to wait until it is finished if you want to modify the configuration and re-run the script."
That STOP link should be prominent on every script page, regardless of mode = cron, background, or foreground.
Right now, I've canceled a background run, restarted manually, and see no such STOP link.