feat: witness n-gon, unapplied-scale, and coincident-vert pathologies

[TMHSDigital]

Summary

• Three synthesized-pathology examples. Gallery stills skipped: none of the defects are thumbnail-legible.
• ngon-triangulate inverts mesh-hygiene-audit / triangulate-tangents.
• unapplied-scale-gltf inverts gltf-export-roundtrip (identity scale) and neighbors prop-origin-transform.
• coincident-vert-weld inverts degenerate-bevel-weld (bevel-pinch coincidences).
• ROADMAP: CC0 fixture vendoring (deferred) + overlapping-UV export as leftover.

Why these three

N-gons, unapplied non-uniform scale, and coincident duplicate verts are the defects that stress contracts this repo already teaches. Overlapping UVs already have a SAT gate and --falsify on lightmap-uv-channel. Zero-area faces are owned by degenerate-bevel-weld.

Type

• feat — new example (minor bump)

Squash-merge subject: feat: witness n-gon, unapplied-scale, and coincident-vert pathologies

Pre-assertions (required)

Example	Pathology exists iff	Detection falsify (exit 3)
ngon-triangulate	1 face / 6 loops / 5 faces	--no-dissolve ngon count 0
unapplied-scale-gltf	scale (2,1,0.5) and local verts ±1	--identity scale (1,1,1)
coincident-vert-weld	16 verts / 8 unique / 12 faces / valence 2	--no-duplicate V=8 unique=8

Handling (second axis)

Example	Contract	Handling falsify (exit 4)
ngon	calc_tangents aborts until triangulate → 4 tris + 4 quads / 28 loops. glTF tris=12 either way.	--skip-triangulate
scale	export_apply is modifiers-only. node.scale Y-up (2, 0.5, 1), POSITION ±1. Vert count 8 either way.	--bake → node.scale None, POSITION x ±2
coincident	glTF 48 pos / 24 tris / 8 unique. remove_doubles → one cube, still manifold.	--weld → 24 pos / 12 tris

Evidence

Live-run-proven (local Windows)

Binaries: .scratch/blender-5.2.1-windows-x64/blender.exe 5.2.1 LTS 9e2066aef7ef; blender-4.5.11-windows-x64 4.5.11 LTS 4db51e9d1e1e.

Both LTS: happy path exit 0; detection flags exit 3; handling flags exit 4. Same closed forms. No skips.

Falsification is local-Windows only (ROADMAP, next to inverted-canary marker-text).

Inspection-only

CI 4.5 job will float (last PR used 4.5.13). export_apply RNA description and Y-up scale permute were read from the live exporter.

Gallery

None. Hexagon-on-cube, stretched box vs modeled size, and coincident cubes do not prove the defect at thumbnail.

Release-owned fields — do not hand-edit

Left at 0.52.0.

Test plan

• 5.2 smoke: all three PASS
• 4.5 smoke: all three PASS (no SKIP)
• validate-counts / manifest: 53 examples
• Socket not pending/failing
• After squash-merge: quote release.yml on the merge SHA; expect RELEASE (bump=minor) → v0.53.0

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