nx_argmacro_probe.nx

nx_argmacro_probe.nx -- MINIMAL repro for arg-macro expansion (id 1785514019). nx_macro_test is a large file with a big import closure and NESTED macro use (MAX's body calls SQ), so its failure cannot distinguish "the mechanism is broken" from "the mechanism works but not at scale / not nested". This isolates ONE arg macro, one use, no nesting, tiny closure. exit 0 = arg expansion WORKS. exit 1 = expanded but wrong value. build failure = mechanism dead. license_tier: ORIGINAL expect_exit: 0