It's:

- in a grounded cell (unsafecell maybuninit)
- as a pub static no mangle (makes the compiler not assume that it's private, and can be escaped outside of the current binary)
- in a separate linker section to regular memory
- uses postcard-rpc keys as the magic number, which means it's an 8-byte value that also means that changing types will make the magic number change
- serializes as postcard data, so there's no problem if bootloader and app are compiled on different compiler versions
- zeroes out the mem on any read/write failure, and in my app I also zero it out after reading