Versioned save schema

versioned-save-schema.gpc

define SAVE_MAGIC = 23117;
define SAVE_VERSION = 2;

int saved_magic;
int saved_version;
int strength;

init {
    saved_magic = get_pvar(SPVAR_1, 0, INT32_MAX, 0);
    saved_version = get_pvar(SPVAR_2, 0, 100, 0);

    if(saved_magic == SAVE_MAGIC && saved_version == SAVE_VERSION) {
        strength = get_pvar(SPVAR_3, 0, 100, 25);
    } else {
        strength = 25;
    }
}

Save magic/version first. Reject or deliberately migrate unknown versions instead of decoding them under a new layout.

Schema table example:

Slot	Field	Range	Default	Version
SPVAR_1	magic	0..INT32_MAX	0	all
SPVAR_2	schema version	0..100	0	all
SPVAR_3	strength	0..100	25	2