nx_det.nx

nx_det.nx -- deterministic floating-point execution mode. WHY THIS EXISTS (Phase R2 capability lever, 2026-04-24): Same .nx source must produce the same bits of output on every host that runs it -- x86 laptop, RV64 Milk-V, NishiOS silicon, browser WASM. This is a capability V8 / WASM / gcc STRUCTURALLY cannot provide because each chooses its own IEEE 754 defaults (rounding mode, subnormal handling, contract-affine math, FMA fusion) and each sees its own platform's ISA-specific quirks. Bit-exact determinism unlocks, in order: 1. Reproducible F6 manifests across heterogeneous build hosts 2. Replay debugging (record input nondeterminism, replay exactly) 3. Lockstep multiplayer (Carthago V3 ask; NGE future) 4. Formal verification at the binary level (seL4 path) 5. Supply-chain attestation of FP-heavy numeric code We own the code path from source to silicon, so we pin every FP knob that the standard leaves flexible. Managed platforms cannot do this because they don't control the ISA or the JIT. WHAT THIS MODULE PROVIDES: nx_det_enter() Enter deterministic mode. Sets: * rounding mode = round-to-nearest-even * subnormals flushed to zero = NO (accept slower runtime, forbid flush-to-zero platform quirk) * NaN handling = quiet propagation, no trap; NaN payload canonicalised * contract-affine math = OFF (no fused multiply-add unless nx_det_fma called) * exception flags cleared nx_det_exit() Restore whatever FP state the caller had. nx_det_with(block) Scope block in deterministic mode; auto restore on return. Convention wrapper.