Amazingly, I'm back up and running.
This command seemed to make the difference:
heimdall flash --kernel zImage --recovery zImage
My uneducated view is this somehow fixed my partition - but I defer to those of you who actually know something (if it makes a difference, the zImage was from my phone originally - an old backup - i.e. it was not something I downloaded). After I did this, I reflashed everything (w/o repartitioning) and was able to reset my system in recovery. Thanks for everyone's help.