Just wanted to update folks:
I went to the Genius Bar and luckily I had a chill guy to work with, which always bodes well for the rest of the service interaction.
He did the Apple diagnostics (not the power on + D, but the more extensive one that only they can run) and the battery came back as "Fine". I feared the worst but the Genius said that its status at 89.09% health (their reading, my Battery Health app said 85%) after 1 year and 163 cycle count is below expected performance. Since it's still within the year warranty (by a few weeks), they'll swap it out for me free of charge.
A happy ending!
He also said this is probably due to me keeping my laptop plugged in all the time even though it's fully charged. I was always under the impression that at 100% and plugged in, it would bypass the battery and work solely from the outlet but he said that's not true and that I have to "use the battery as a battery". Any thoughts?