I used to use ext2online in conjunction with LVM whenever I had to resize a partition that was already mounted. I haven’t had to do that in a while, so I was surprised that I couldn’t find ext2online anymore.
Turns out more modern versions of resize2fs already know how to do that. Not the ones from e2fsprogs=conary.rpath.com@rpl:1, but I was able to install e2fsprogs=conary.rpath.com@rpl:devel into a temporary root and run the new resize2fs from there. Yay.