I've left a new message on the root topic from which this one was spun off. I will include it in full below. Thanks to every user who spared time to help out here.
Hello again, Microsoft Answers Community.
First and foremost, I wanted to take the time to thank everyone who spared the time to help me out with this issue, both on this forum and others, over the past thirteen-and-a-half months. Admittedly, it would have been nice to have more users engage with me here over that time so that I wouldn't have needed to join so many forums and create so many topics to resolve the problem, but whoever did engage to help out, thank you, regardless. The effort was truly appreciated. Each of you tried to help me navigate my way through every frustrating twist and turn of the repair effort, whether it was backing up the hard drive, opening the laptop, or trying to create external rescue media most recently; the whole ride was driving me bonkers, so I also thank everyone who commented for your patience and empathy wherever given. A thousand times over, thanks for everything.
Which brings me to why I've returned: in the past few weeks, I finally broke down and managed to pull together the funds to sign up for the HP SmartFriend Service, albeit begrudgingly. Working with one of the HP SmartFriend technicians via teleconference (as well as a Staples technician prior to that -- thank you for your help, Steven), it was determined that the hard drive was clear in another collection of scans, and through HP SmartFriend, I ended up purchasing the installation media USB through them. Several days later (about a week ago now), another SmartFriend teleconference led me through the reinstallation attempt, only to receive a series of error messages; from the results, the technician determined that the errors pointed to a fundamental problem that never rested in the software at all. Apparently, the root cause of the "Automatic Repair" reboot loop was a malfunction in the laptop's motherboard all along; as such, it was never feasible to correct the matter at home on my own, with or without professional guidance. Based on that, the only options to fix the error are to either surrender it to a professional for repairs, or to simply invest in a new laptop altogether -- whichever may come first.
So, yes, I got that bad news fairly recently. Facts are stubborn and depressing things sometimes; while I can accept the answer as to why the problem occurred, I hate that it took more than a year to find that answer in the first place. Since I don't currently have the estimated $300-$400 available to pay HP to fix the defective motherboard, I'll just close the topic with this reply as my "answer" to the question.
Sorry to say I couldn't solve the problem in a way that could help other users; at best, anyone else with this "Automatic Repair" reboot loop might want to consider that it's a hardware issue rather than a software problem.
To anyone currently facing the same problem, I wish you the best of luck.