feat: add degenerate-bevel-weld example (#112)

Isolates the half-dimension bevel collapse found authoring
gltf-export-roundtrip: a slab beveled at offset == min_dim/2 pinches
its band into exactly 12 zero-area faces (4 min-axis edges x 3
segments) with 16 coincident verts (4 x (segments+1)) and min_area down
3.2e5x, while the safe offset yields none. The export angle is the
point: a stdlib re-parse of the shipped GLB recomputes every triangle
area from raw POSITION + indices buffers and counts 32 degenerate
triangles crossing the boundary (MEASURED regression constant,
re-measure recipe in check) versus 0 for the safe mesh — the loops an
engine merge-by-distance welds. Probed five regimes to ground the
closed forms (clamp on/off x safe/half/over, modifier vs bmesh path).
Byte-identical on 4.5.11 and 5.1.2. Falsified: safe offset at threshold
(exit 3), degenerate offset below it (exit 4), coincident closed form
corrupted (exit 6), GLB census off (exit 8). Render path gated with
check_framing (0.794x/0.356y, margins >= 0.100); dual tray with
live-data seam markers. Count prose bumped to 40 across
README/CLAUDE/AGENTS.

Signed-off-by: fOuttaMyPaint <TMhospitalitystrategies@gmail.com>

Author: TMHSDigital

.cursor-plugin/plugin.json

@@ -69,6 +69,7 @@
     "examples/curve-bevel-arc",
     "examples/custom-normals-shade",
     "examples/damped-track-aim",
+    "examples/degenerate-bevel-weld",
     "examples/depsgraph-export",
     "examples/driver-wave",
     "examples/gltf-export-roundtrip",

.github/workflows/blender-smoke.yml

@@ -554,3 +554,15 @@ jobs:
           # non-zero on failure.
           xvfb-run -a "$BLENDER" --background \
             --python examples/attribute-domain-shear/attribute_domain_shear.py --
+
+      - name: Shipped example - degenerate bevel weld (half-dimension collapse)
+        run: |
+          set -euo pipefail
+          # Check only (no render): a 1.6x0.4x1.0 slab beveled at safe (0.10)
+          # and threshold (0.20 == min/2) offsets; asserts zero vs exactly 12
+          # zero-area faces (4 min-axis edges x 3 segments), 16 coincident
+          # verts (4 x (segments+1)), min_area collapse > 1e5x, and a stdlib
+          # GLB re-parse counting 32 degenerate triangles shipped versus 0.
+          # Exits non-zero on failure.
+          xvfb-run -a "$BLENDER" --background \
+            --python examples/degenerate-bevel-weld/degenerate_bevel_weld.py --

AGENTS.md

@@ -20,7 +20,7 @@ a `.cursor-plugin/plugin.json` manifest so the ecosystem drift checker
 classifies it as a `cursor-plugin`. This is content the AI loads when the user
 asks Blender questions or works on Blender add-ons in Cursor or Claude Code.
 
-The content base is 12 skills, 6 rules, 2 templates, 17 snippets, and 39
+The content base is 12 skills, 6 rules, 2 templates, 17 snippets, and 40
 examples (counts are CI-enforced against README.md and the manifest). The full
 inventory tables and per-item purposes live in `CLAUDE.md`. Example anatomy
 and authoring rules: copy `examples/bmesh-gear/`; the render look is specified
@@ -35,7 +35,7 @@ Blender-Developer-Tools/
   rules/<rule-name>.mdc          # 6 rule files
   templates/<template-name>/     # 2 starter templates
   snippets/<snippet-name>.py     # 17 standalone Python snippets
-  examples/<name>/               # 39 runnable smoke-gated examples (+ gallery.json)
+  examples/<name>/               # 40 runnable smoke-gated examples (+ gallery.json)
   examples/gallery_framing.py    # shared Layer 1 framing measurement (render path only)
   scripts/build_gallery.py       # generates docs/gallery/ (stdlib only)
   scripts/site/                  # vendored landing-page build (build_site.py + template)

CLAUDE.md

@@ -21,7 +21,7 @@ skills/<skill-name>/SKILL.md   - AI workflow definitions, 12 total
 rules/<rule-name>.mdc          - Anti-pattern rules, 6 total
 templates/<template-name>/     - Starter projects, 2 total
 snippets/<snippet-name>.py     - Standalone code patterns, 17 total
-examples/<name>/               - Runnable smoke-gated examples, 39 total (+ gallery.json)
+examples/<name>/               - Runnable smoke-gated examples, 40 total (+ gallery.json)
 scripts/build_gallery.py       - Regenerates docs/gallery/ from gallery.json (stdlib only)
 scripts/site/                  - Vendored landing-page build (Jinja2)
 docs/gallery/                  - Committed generated gallery pages + hero renders
@@ -82,11 +82,11 @@ v0.1.0: canonical object creation and deletion, depsgraph evaluated mesh, bmesh
 
 v0.2.0: Principled BSDF material, driver-with-custom-function via `driver_namespace`, application handler registration, shader node group with cross-version `interface` API, `foreach_get` bulk vertex read, version-branch skeleton, and USD export with `evaluation_mode='RENDER'`.
 
-## Examples (39)
+## Examples (40)
 
 Runnable scripts at `examples/<name>/`, each asserting a real API contract with
 deterministic checks (exit non-zero on failure) and optionally rendering a still via
-`--output`. All thirty-nine run headless on Blender 4.5 LTS and 5.1 in `blender-smoke.yml`;
+`--output`. All forty run headless on Blender 4.5 LTS and 5.1 in `blender-smoke.yml`;
 their renders ship in the site gallery at `docs/gallery/`. `examples/gallery.json` is the
 gallery's source of truth. When authoring a new one, copy the anatomy of
 `examples/bmesh-gear/` (script structure, README shape, dark-studio render recipe) and

README.md

@@ -18,7 +18,7 @@
 </p>
 
 <p align="center">
-  <strong>12 skills</strong> &nbsp;&bull;&nbsp; <strong>6 rules</strong> &nbsp;&bull;&nbsp; <strong>2 templates</strong> &nbsp;&bull;&nbsp; <strong>17 snippets</strong> &nbsp;&bull;&nbsp; <strong>39 examples</strong>
+  <strong>12 skills</strong> &nbsp;&bull;&nbsp; <strong>6 rules</strong> &nbsp;&bull;&nbsp; <strong>2 templates</strong> &nbsp;&bull;&nbsp; <strong>17 snippets</strong> &nbsp;&bull;&nbsp; <strong>40 examples</strong>
 </p>
 
 <p align="center">
@@ -760,6 +760,26 @@ palette[K−1], and the measured shear matches the palette closed form
 `active_color`, the shader Attribute node). The broken state is in-frame:
 the right pinwheel is the falsification variant.
 
+</td>
+</tr>
+<tr>
+<td width="46%" valign="middle">
+<a href="examples/degenerate-bevel-weld/"><img src="examples/degenerate-bevel-weld/preview.webp" alt="Degenerate bevel weld: two teal display trays side by side — left with a soft rounded bevel, right collapsed to a knife edge with orange seam markers at the zero-area face centroids, proving the half-dimension bevel collapse ships degenerate triangles" /></a>
+</td>
+<td valign="middle">
+
+### [degenerate-bevel-weld](examples/degenerate-bevel-weld/)
+
+The half-dimension bevel collapse, isolated. A slab beveled at
+`offset == min_dim/2` pinches its band into exactly **12 zero-area faces**
+(4 min-axis edges × 3 segments) with 16 coincident verts and `min_area`
+down 3.2e5× — and a stdlib re-parse of the exported GLB counts **32
+degenerate triangles shipped** to disk, where an engine merge-by-distance
+welds their loops. Companion to
+[`gltf-export-roundtrip`](examples/gltf-export-roundtrip/) (where the count
+check first caught the weld) and [`mesh-hygiene-audit`](examples/mesh-hygiene-audit/)
+(topology gates). Seam markers are placed from live mesh data.
+
 </td>
 </tr>
 </table>

ROADMAP.md

@@ -109,7 +109,7 @@ Not committed; target list for the next content version. (v0.3.0 shipped the smo
 - ~~Triangulate + tangent-space witness~~ **SHIPPED** as `examples/triangulate-tangents/` — `calc_tangents` aborts on any ngon (back cap must be an explicit fan); mikktspace matches the edge/UV-delta formula within welding tolerance on smooth fields (2.3e-6 measured); planar UVs on a cylindrical wall collapse tangents onto normals (dot 0.998); `MeshUVLoopLayer` handle dangles across `calc_tangents()` on 4.5 (471 phantom flips, silent exit 0) while the mikktspace math is byte-identical on 4.5.11 and 5.1.2
 - UV-handle lifetime snippet: re-fetch attribute/UV layers by name after any CustomData-reallocating call (`calc_tangents`, `VertexGroup.add`, modifier edits) — held handles dangle silently on 4.5, survive by luck on 5.1 (found authoring `triangulate-tangents`)
 - glTF skinned-mesh export witness: follow-up to `gltf-export-roundtrip` + `vertex-weight-limit` — **SHIPPED** as `examples/gltf-skin-roundtrip/` — `skins[0].joints` names every bone, JOINTS_0/WEIGHTS_0 with unit sums (3e-8), weights bit-exact, rest matrices to 2.4e-07, deformation to 4.8e-07; exporter welds duplicate loops (sorted-multiset comparisons mispair — compare by rest-key); unparented skinned meshes make the exporter bind an armature by name
-- Degenerate-bevel weld hazard (snippet or rule): bevel width ≥ half a box dimension creates zero-area faces whose loops weld on glTF export (found authoring `gltf-export-roundtrip`, where the count check caught a 36-vertex weld)
+- ~~Degenerate-bevel weld hazard~~ **SHIPPED** as `examples/degenerate-bevel-weld/` — at `offset == min_dim/2` the bevel band collapses to exactly 12 zero-area faces (4 min-axis edges × 3 segments) with 16 coincident verts (4 × (segments+1)) and min_area down 3.2e5×; a stdlib GLB re-parse counts **32 degenerate triangles crossing the export boundary** (MEASURED regression constant) versus 0 for the safe mesh — the loops an engine merge-by-distance welds; byte-identical on 4.5.11 and 5.1.2
 - ~~GAMMA_CROSS blend-curve witness~~ **SHIPPED** as `examples/vse-gamma-cross/` — the cross blends in a gamma-0.5 space: `((1-t)·√A + t·√B)²` with `t = (frame − start)/duration`, never 1 inside the effect; mid-cross dips 0.115 below the sRGB lerp from crimson/teal (closed form (0.341, 0.349, 0.463) confirmed per frame); AgX-default sampling poisons the fit (0.146 red-channel error, `view_transform='Standard'` mandatory); deleting a consumed input orphans-and-deletes the effect — follow-up to `vse-cut-list`
 - Falsy `bpy_prop_collection` trap snippet: an empty collection is falsy, so `editor.strips or editor.sequences` silently falls through to the legacy accessor on an empty timeline — always branch on `hasattr`; likely generalizes across the API (found authoring `vse-cut-list`)
 - ~~Collision compound witness~~ **SHIPPED** as `examples/collision-hull-proxy/` — game-prop collision as a compound of convex pieces, each a `bmesh.ops.convex_hull` of a coarse `sec(π/n)`-inflated cage (containment 4.4e-08, watertight, positive signed volume, Euler 2, per-piece 255-face budget: body 70, caps 60×3, compound 250); a hull of the dense render mesh measures 380 faces — over budget — which is why pipelines hull cages; proud details cost cage rows, concave grooves are free; byte-identical on 4.5.11 and 5.1.2