nx_smoke_nxc_tilde.nx

nx_smoke_nxc_tilde.nx -- 1:1 proof that the SELF-HOSTED RV64 backend (nx_riscv.nx) lowers `~` (OP_NOT) to `xori rd, rs, -1`. Mirrors nx_smoke_nxc_pipeline.nx but (a) the demo exercises `~` on a non- foldable parameter and (b) it WRITES the emitted RV64 asm to stdout so the gate can grep for the `xori ..., -1` one's-complement and confirm the OP_NOT lowering really fires (not the silent drop that existed before). Then it still assembles, proving nxasm accepts it. exit code: code_len & 0xFF on success (>0), or an error sentinel. license_tier: ORIGINAL