Recovering after a root-partition resize gone wrong

All of my root partitions are raw partitions. "All"? Yes I have several root partitions, all raw. Raw so that other considerations like LVMs don't interfere when I need to work on them.

I have my main root partition for everyday use. Just like everybody does.

I have a secondary root partition which acts as a lifeboat if something dies in the main root partition. It also allows the main root partition to be unmounted and worked on separately, if perchance it needs resizing or some other operation.

Thirdly, I have another root partition set aside purely for experimentation with other distros. Sometimes I will begin to use the third root partition's distro as my secondary lifeboat distro and then the second root partition as my experimentation partition.

Whatever, I have use for and always keep 3 root partitions. That disk space is cheap insurance.