nx_gamesave.nx

nx_gamesave.nx -- the SOVEREIGN SAVE/LOAD PART. nx_gamebench ranked this #1: save-load-persistence was PARTIAL and blocked 11 of the 12 benchmarked reference titles -- the highest-demand missing capability in the whole game ecosystem, found by demand-ranking rather than by eye. WHAT WAS ACTUALLY MISSING: runtime/nx_save_slot.nx already signs a combined hash over two in-memory chromatin snapshots -- but it never writes bytes to disk, never reads them back, and has no gate. A game cannot save with it. This organ is the missing half: arbitrary game state <-> a durable file. Built as a CERTIFIED COMPOSABLE PART per knowledge/registry/game_parts.tsv doctrine ("build each part to exceed ONCE, then compose forever"), so every future emitted game inherits these properties for free: 1. BIT-EXACT ROUND-TRIP -- save->load->save is byte-identical. Our stack is all-integer with no float and no hidden clock (saved_at is CALLER-SUPPLIED on purpose), so a save file is reproducible. This is the determinism exceed carried into persistence; most engines cannot claim it. 2. ATOMIC -- write to .tmp, fsync, rename. A crash mid-save can never leave a torn save file. A reader only ever observes a complete file. 3. CORRUPTION REFUSED LOUD -- a single flipped byte fails the checksum and load returns an error code. It never hands back half-valid state. (The classic "corrupt save eats an 80-hour run" bug.) 4. FUTURE-VERSION REFUSED -- a newer format is rejected rather than misparsed. 5. ADDITIVE-ONLY (rule 13) -- saving over a slot banks the previous bytes as .prev. History is not destroyed, so a bad save is always recoverable. Self-contained (imports only nx_syscalls + the pure core) so it runs on the NAS as an MCP tool. seq1151 (2026-07-30): the byte<->i64 and rolling-fold MECHANISM moved to nx_gamesave_core.nx -- the ONE definition shared with the wasm save-image surface (nx_wasm_craft). This file is the FILE surface: atomicity, .prev banking, refusal codes. Format bytes UNCHANGED (gate-proven). license_tier: ORIGINAL expect_exit: 0