nx_gamesave_core.nx

nx_gamesave_core.nx -- the PURE serialize/validate core of the save law (seq1151 design-flaw fix). nx_gamesave.nx (file surface, native) and nx_wasm_craft.nx (save-image surface, wasm) each carried their OWN copy of the same mechanism -- little-endian i64<->bytes and the rolling xor-multiply-mask checksum fold -- because gs_save is file-syscall-coupled and wasm code cannot call it. That parallel re-derivation was the bug. This core is the ONE definition; each format's constants (seed, multiplier, mask, granularity) are PARAMETERS, so both existing on-disk formats stay byte-identical while the mechanism has a single home. PURE BY CONSTRUCTION: imports NOTHING, allocates NOTHING, touches no syscall -> wasm-dialect-clean. license_tier: ORIGINAL expect_exit: 0