Functions
	artifacts (boxes3d, tmp_path)

	test_skin_face_counts (boxes3d)

	test_gap_metric_on_input (boxes3d)

	test_fitting_constraint_is_positive_diagonal (artifacts)

	test_laplacian_rows_sum_to_zero (artifacts)

	test_collision_proxy_outward_and_body_ids (artifacts, boxes3d)

	test_union_region_selects_both_skins (boxes3d)

	test_whole_boundary_and_filter_agree_on_interior_bodies (boxes3d)

	test_underscore_rejected (boxes3d)

Detailed Description

Tier 1 — make_interface_constraint artifacts on a synthetic 3D mesh,
plus a self-check of the gap metric the separation test relies on.

Variable Documentation

list test_interface_constraints.SELS

Initial value:

1= [{"region": "tag_0", "filter": "ambient", "id": 1},

2 {"region": "tag_1", "filter": "ambient", "id": 2}]