nx_macro_axis_gate.nx

nx_macro_axis_gate.nx -- mechanically prove the BACKEND-OWNED TARGET AXIS of the self-host preprocessor. Closes debt 1785516163, which asked for exactly this: a gate that FAILS if a compiled corpus ever resolves TARGET_X86_64 as DEFINED, so the pin is held by a MECHANISM instead of a comment. WHY THIS MATTERS MORE THAN IT LOOKS. The x86 self-host emits through x86ctx_rv64_to_x86_64_syscall, which expects source to carry RV64 syscall numbers and translates them at emit time. So: TARGET_X86_64 MUST be UNDEFINED -> the @ifndef branch (RV64 numbers) is the live one TARGET_RV64 MUST be DEFINED -> the source axis, the exact complement If someone fixes the preprocessor by predefining TARGET_X86_64 as an ordinary macro -- the natural looking change when adding a macro table -- the raw-x86 branch of nx_syscalls / nx_hal / nx_dirent / nx_poll / nx_probe / nx_fcntl / nx_self_build switches on, and EVERY syscall const is then translated TWICE. Silent ecosystem-wide corruption, not a build error: the binaries still link and still run, they just call the wrong kernel entry points. A comment cannot stop that. This gate can. NON-VACUITY BY CONSTRUCTION. Every block that MUST be dropped contains a poison identifier that does not exist anywhere in the corpus. If a drop path ever fails, the poison reaches the parser and THE BUILD FAILS. So this gate cannot pass vacuously -- a preprocessor that ignored @ifdef entirely could not compile this file at all. expect_exit: 0 license_tier: ORIGINAL