Update: the bolt was the correct one; the package even said "Caliper Bracket Bolt" on it. Silly Advance Auto site. Used some red loctite, torqued to 85lb/ft, then went through all the other caliper bracket bolts. Sure enough, the ones on the driver's side were barely more than hand-tightened. Seems like whoever was responsible for this job just tightened them all "snug" and never got around to torquing them down. It didn't seem like there was any evidence of thread lock, either. Really disappointing. I've always had good luck with this shop in the past, but may need to find a new one. I did send the owner a message with the photos of the missing bolt in the hopes that he'll use it as a learning opportunity about the dangers of putting quick turnaround over everything else.
While I was down there, I replace the swaybar bushings with some new Moog parts. Whoa. Can't believe what a difference that 10 minute job made on the ride quality and handling. Under all the gunk of layers of fluid film and grease, the old ones were white and hollow inside - that can't be OEM, right? They were really squishy and compressed. Seriously, it's a night-and-day difference. Next up will be end links and bushings. I'm actually feeling like the shocks may be ok after all.