nx_isa_conform_gate.nx

nx_isa_conform_gate.nx -- THE ISA CONFORMANCE RULER. WHY IT EXISTS: the estate carries TEN sovereign ISA emulators in NishiLang (rv64 arm64 armv7a cortexm loongarch64 mips64 ppc64le riscv32 s390x sparc64). Measured 2026-09-03 by nx_catalog: all ten are SOURCE-ONLY -- 0 built, 0 promoted, 0 registered, 0 invoked -- ONE of them had a KAT (rv64), two more had x86 tests, and the only differential proof in the estate was bench/gate_nx_emu_diff.sh, a SHELL script that needs WSL plus riscv64 binutils plus qemu in order to judge anything. Eight emulators had never been measured at all. THE LAW THIS ORGAN OBEYS: a capability asserted and never measured is a claim, not coverage. "We emulate MIPS64" is decided by running MIPS64 machine code, in process, against values taken FROM THE ISA MANUAL -- never from the emulator's own source, which would calibrate the ruler to the subject it is meant to judge. FIVE OUTCOMES, NEVER ONE: PASS ran and matched the manual-derived expectation WRONG-ANSWER ran to completion and computed the wrong value UNSUPPORTED hit an instruction class the emulator does not implement RAN-OFF-END the interpreter loop ended without an exit syscall FAULT bad PC, out-of-range access, or the step budget Collapsing these into "FAIL" is what makes a gap unactionable: an unimplemented instruction class and a miscomputed result need OPPOSITE fixes, and only the first is a missing feature. CORRECTION, 2026-09-03: the first cut of this header claimed "neither emulator can return -2, so the codes do not collide with a real answer". THAT WAS FALSE and I wrote it without reading far enough: nx_emu_rv64.nx line 50 defines EMU_RV_RANOFF = -2 and line 123 uses it as the INITIAL value of result, so -2 is exactly what comes back when the loop ends with no exit syscall. Treating it as WRONG-ANSWER would have reported a structural non-completion as an arithmetic disagreement -- the same two-conditions-under-one-negative-word defect this organ was written to refuse, committed inside the organ that refuses it. Both exit paths mask with & 0xff (rv64 line 302, mips64 SYSCALL), so a real answer is always 0..255 and the three negative sentinels cannot collide with one.