> It seems writing to one file system is likely to destroy the other, since they would be unaware of each other's allocated blocks.
The entirety of ext2 stays within FAT32's reserved blocks (that is, between the bootsector and the File Allocation Table), so FAT32 won't write over ext2. The inverse is also true, as ext2 knows its formatted size, so it won't write outside of the reserved sectors.
Yes, they just don't interact with each other.
> It seems writing to one file system is likely to destroy the other, since they would be unaware of each other's allocated blocks.
The entirety of ext2 stays within FAT32's reserved blocks (that is, between the bootsector and the File Allocation Table), so FAT32 won't write over ext2. The inverse is also true, as ext2 knows its formatted size, so it won't write outside of the reserved sectors.