nxengine/extract-auto/sprites_sif.h should become a plain text file.

Currently, the binary data of sprites.sif resides in nxengine/extract-auto/sprites_sif.h which is not readable by human or sifedit.

https://github.com/andwn/cave-story-md/blob/master/res/resources.res looks like the plain text equivalent to sprites.sif

sifedit from the upstream nxengine project may stop working in the near future.
https://github.com/nxengine/sifedit is also fragile and is hated by nxengine-evo's maintainer.
Plain text configuration is the way forward.

sprites.sif should become a plain text file such as sprites.txt. Makefile can compile the plain text file into a C header during compile time.
nxengine/sprites.txt in retroarch systems folder may override the built-in sprites configuration.

sprites.txt should be well documented with comments so that anyone can edit it.

Start by comparing nxengine/extract-auto/sprites_sif.h with the plain-text example at res/resources.res, then inspect the Makefile and nxengine/sprites.txt override location. Define the text format and document it with comments, while preserving compilation into the built-in sprite configuration and allowing the external override described in the issue.