nx_eng_diff_miscompile_test.nx

nx_eng_diff_miscompile_test.nx -- prove the ENGINEER's differential logic-miscompile detector, and MONITOR the live compiler with it. GATE (must hold): the detector mechanism is sound (agree on equal, diverge on unequal) AND the trusted memory-staged reference equals the known answer. MONITOR (reported): whether the HIGH-register-pressure form diverges -- the known-open class the full-pipeline gate is blind to. A divergence here is the canary firing, not a regression in this test. main() is kept low-pressure (delegated compares, memory-backed verdicts) so the gate itself is not a victim of the very bug it watches for.