nx_procgen_terrain_gate.nx

nx_procgen_terrain_gate.nx -- Gx/PROCGEN: rule-grounded, seed-diverse procedural terrain (the Infinigen direction: procedural, asset-free, parametric-for-diversity, NOT random noise). FBM value-noise heightfield -> D8 flow-direction -> flow-accumulation (descending-elevation pass = a real WATERSHED) -> rivers that PROVABLY flow downhill (the clay-audit named "rivers that don't flow downhill" as the failure) -> shaded-relief render (hillshade x altitude colormap, rivers blue). Three SEEDS side-by-side = parametric diversity (don't overfit to one environment). All integer, deterministic, sovereign. Honest: this is coherence rung 1, not photoreal yet. D001 MIGRATION 2026-09-02 (procgen PG19): the verdict was hand-rolled (PASS/FAIL prints, a fails counter, sys_exit(1)), so /api/promote refused it and nothing outside could read its outcome. Every tooth is now a gv_check and the exit code IS the verdict (nx_gate_verdict). The measurements, thresholds and the PNG are unchanged. license_tier: ORIGINAL expect_exit: 0