nx_scratch_probe.nx

nx_scratch_probe.nx -- R0.0b proof kernel: uses the WASM-lane nx_scratch to allocate DISTINCT framed buffers, the multi-word-local idiom that the wat lane previously had no allocator for. If nx_scratch handed back the same address (the old no-op-alloca failure mode), a and b would alias and the sum would be wrong; distinct buffers give the correct native-equivalent answer. Pure (imports only nx_wasm_scratch).