nx_auto_supports_v2_target_test.nx

nx_auto_supports_v2_target_test.nx -- four-pillar MONITOR for the auto-supports mushroom miss surfaced by Phase B2.1 (commit prior). This test EXPECTS the bug -- it will FAIL loudly when the v2 fix lands, signalling to update assertions. The bug: nx_slice_pipe_build_supports does NOT detect overhangs on a clean mushroom shape (column 4x4 + cap 10x10 with 3mm shoulder). Empirically: - Direct call to nx_supports_layer_overhang with the column polygon and cap polygon DOES detect overhang vertices (verified by background diagnostic, exit 0) - So the primitive math works. The bug is in the slicer integration: contour-build at z=20.0 coplanar slice, or contour pairing by index at the transition layer, or layer indexing skipping the mushroom shoulder. V2 fix queued (not in this commit): - Contour-centroid tracking for matching across layers - Cumulative-printed-region check (vertex outside any prev layer's contour => overhang) - Handle abrupt shape change (single-vs-multi-contour transitions) When v2 ships, this smoke's expected verdict flips from "v1 misses (plan.n == 0)" to "v2 detects (plan.n > 0)". The body literally says `expect plan.n == 0` -- which means the test FAILS LOUD if v2 ships without updating this smoke. That's the MONITOR pillar. expect_exit: 0 (current: v1 returns plan.n=0; expect that) license_tier: ORIGINAL