It's amazing how often highly-polished web infrastructure gets put into the trash in pursuit of narrow objectives like avoiding a full page load. Very few applications actually benefit from being a single page. You tend to lose a lot more than you gain in terms of UX.
TIL that this (or rather, the lack of this) is why some pages show that annoying "do you want to resubmit your post" notification, but not others, and the name for it. Thank you!