nx_eng_diff_miscompile.nx

nx_eng_diff_miscompile.nx -- the ENGINEER's DIFFERENTIAL miscompile detector. The full-pipeline gate (nx_engineer_gate_runner) catches crashes and compile-fails; it is BLIND to a LOGIC miscompile -- a wrong result from correct-looking code. The known-good compiler does exactly this under register pressure (a value held live across many calls is not spilled, so a later comparison reads garbage and flips -- see project-knowngood-compiler-regpressure-miscompile-2026-06-03). This detects that class by DIFFERENTIAL execution: compute the SAME logical value two structurally different ways and flag any divergence -- ed_hp HIGH register pressure: the value is held live across many ed_noise() calls, then tested (the exact shape that miscompiled rc_bad / v1). ed_lp LOW pressure: the value is staged in MEMORY and reloaded for the test. Both must equal the compile-time-known answer (K = -3 -> "is K<0?" -> 1). If ed_hp disagrees with ed_lp or with the known answer, a logic miscompile is present. RACI: detection only -- the Engineer reports; it does not fix or admit. license_tier: ORIGINAL