fix: showcase quality pass — stone-well and cart

docs/gallery/index.html

@@ -903,7 +903,7 @@ <h2><a href="shipping-crate/">shipping-crate</a></h2>
         <div class="card-body">
           <h2><a href="stone-well/">stone-well</a></h2>
           <p class="teaches">A procedural stone well through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than an API contract.</p>
-          <p class="witnesses"><span class="tag">witnesses</span> Recomputed: 8388 tris, three materials, UVs in 0..1 with zero AABB overlap, outer AABB 1.640×1.640×1.688 m, LOD ratios in band, convex collider 230 tris, non-empty glTF. --skip-decimate exits 9 on the LOD1 ratio budget.</p>
+          <p class="witnesses"><span class="tag">witnesses</span> Recomputed: 9380 tris, three materials with face floors, UVs in 0..1 with zero AABB overlap, outer AABB 1.640×1.640×1.761 m, LOD ratios in band, convex collider 306 tris, hygiene zero (loose, non-manifold, doubles, n-gons), grounded zmin, non-empty glTF. --skip-decimate exits 9 on the LOD1 ratio budget; --lift-z exits 16 on the grounded budget.</p>
           <a class="card-link" href="stone-well/">View example <span aria-hidden="true">&rarr;</span></a>
         </div>
       </article>
@@ -1002,7 +1002,7 @@ <h2><a href="watchtower/">watchtower</a></h2>
         <div class="card-body">
           <h2><a href="cart/">cart</a></h2>
           <p class="teaches">A procedural two-wheel wooden cart through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than an API contract.</p>
-          <p class="witnesses"><span class="tag">witnesses</span> Recomputed: 2572 tris, two materials with 100 metal faces, UVs in 0..1 with zero AABB overlap, outer AABB 1.547×0.749×0.656 m, LOD ratios in band, convex collider 306 tris, non-empty glTF. --skip-decimate exits 9 on the LOD1 ratio budget.</p>
+          <p class="witnesses"><span class="tag">witnesses</span> Recomputed: 2600 tris, two materials with metal and wood face floors, UVs in 0..1 with zero AABB overlap, outer AABB 1.539×0.749×0.640 m, LOD ratios in band, convex collider 122 tris, hygiene zero (loose, non-manifold, doubles, n-gons), grounded zmin, non-empty glTF. --skip-decimate exits 9 on the LOD1 ratio budget; --lift-z exits 16 on the grounded budget.</p>
           <a class="card-link" href="cart/">View example <span aria-hidden="true">&rarr;</span></a>
         </div>
       </article>

docs/gallery/iron-cauldron/index.html

@@ -265,7 +265,7 @@ <h1>iron-cauldron</h1>
 <h2>Budgets</h2>
 <p>Declared as named constants; every gate <strong>recomputes</strong> from the mesh, materials, UVs, evaluated LOD, collider, or export file.</p>
 <p>| Axis | Declared | Measured (4.5.11 / 5.1.2 / 5.2.1) | | --- | --- | --- | | Base triangles | 3280–3520 | 3388 / 3388 / 3388 | | LOD1 ratio | 0.32–0.62 of base | 0.5000 / 0.5000 / 0.5000 | | LOD2 ratio | 0.10–0.35 of base | 0.2196 / 0.2196 / 0.2172 | | Materials | exactly 2 distinct, ≥12 wood, ≥24 metal | 2 slots, 450 wood, 1198 metal | | UVs | in <code>0..1</code>, AABB overlap ≤ 1e-5 | in range, overlap 0 | | Outer AABB | (1.013, 0.986, 0.827) m ± 0.01 | (1.0128, 0.9865, 0.8271), zmin 0.002 | | Pot–leg clearance | ≥ 0.04 m (recomputed vs pole axes) | 0.0513 / 0.0513 / 0.0513 | | Collider tris | ≤ 200 | 98 | | Export | written, size &gt; 0 | 245060 / 245060 / 245044 bytes |</p>
-<p>DECIMATE COLLAPSE triangle counts are <strong>not</strong> identical across series — 5.2.1 is 4 tris leaner on LOD2. The gate is a ratio band, not an exact count. Bake pixels are stochastic; the gate is <code>has_data</code> plus operator <code>FINISHED</code>, not byte-identity. Construction uses no RNG. Export byte counts differ by 12 B on 5.2.1 (glTF serializer), not a gated axis.</p>
+<p>DECIMATE COLLAPSE triangle counts are <strong>not</strong> identical across series — 5.2.1 is 8 tris leaner on LOD2. The gate is a ratio band, not an exact count. Bake pixels are stochastic; the gate is <code>has_data</code> plus operator <code>FINISHED</code>, not byte-identity. Construction uses no RNG. Export byte counts differ by 16 B on 5.2.1 (glTF serializer), not a gated axis. The pot–leg clearance is recomputed from shell verts vs the three pole axes; clipping exits 3.</p>
 <p><code>--skip-decimate</code> skips the LOD DECIMATE stage so LOD1 ratio is 1.0 and exit 9 fires. That is the named budget the falsifier violates.</p>
 <h2>Run</h2>
 <pre><code>blender --background --python iron_cauldron.py --

showcase/README.md

@@ -43,6 +43,13 @@ entry in `showcase/gallery.json`, and a rendered still.
   characteristic 2 — that is a single-shell contract. Pairs of parts
   meant to touch assert a BVH surface gap below a named epsilon
   (vert-vert is the wrong metric for thin straps and collars).
+- **Material face floors.** Every declared material asserts a named
+  minimum face count on the finished mesh, recomputed from
+  `polygon.material_index`. This catches the slot-assignment wipe class:
+  `obj.data.materials.clear()` resets every polygon's `material_index`
+  to 0 on some versions, which renders the piece single-material while
+  the slot count still passes. Assign slots by index-preserving
+  append/replace, never clear-and-rebuild.
 - **Exit codes** are file-local: `0` success, argparse `2`, `3` and above
   in check order. `9` is legal. FATAL `sys.exit(1)` is a crash, never a
   named check.

showcase/cart/README.md

@@ -21,14 +21,17 @@ materials, UVs, evaluated LOD, collider, or export file.
 
 | Axis | Declared | Measured (4.5.11 / 5.1.2 / 5.2.1) |
 | --- | --- | --- |
-| Base triangles | 2470–2680 | 2572 / 2572 / 2572 |
+| Base triangles | 2470–2900 | 2600 / 2600 / 2600 |
 | LOD1 ratio | 0.32–0.62 of base | 0.5000 / 0.5000 / 0.5000 |
-| LOD2 ratio | 0.10–0.35 of base | 0.2193 / 0.2193 / 0.2146 |
-| Materials | exactly 2 distinct, ≥24 metal faces | 2 slots, 100 metal |
+| LOD2 ratio | 0.10–0.35 of base | 0.2200 / 0.2200 / 0.2154 |
+| Materials | exactly 2 distinct, metal ≥ 24, wood ≥ 800 faces | 2 slots, floors met |
 | UVs | in `0..1`, AABB overlap ≤ 1e-5 | in range, overlap 0 |
-| Outer AABB | (1.547, 0.749, 0.656) m ± 0.01 | (1.5473, 0.7486, 0.6560), zmin 0 |
-| Collider tris | ≤ 360 | 306 |
-| Export | written, size > 0 | 202500 / 202500 / 202492 bytes |
+| Outer AABB | (1.539, 0.749, 0.640) m ± 0.01 | (1.5393, 0.7486, 0.6400) |
+| Grounded | bbox min Z within 1e-4 of 0 | 0.0000 / 0.0000 / 0.0000 |
+| Hygiene | loose V/E, non-manifold, zero-area, doubles @1e-5, n-gons: all 0 | 0 / 0 / 0 on every axis |
+| Material-island gap | metal↔wood min distance ≤ 0.008 m | 0.00000 / 0.00000 / 0.00000 |
+| Collider tris | ≤ 360 | 122 |
+| Export | written, size > 0 | 201048 / 201048 / 201032 bytes |
 
 DECIMATE COLLAPSE triangle counts are **not** identical across series —
 5.2.1 is more aggressive on LOD2. The gate is a ratio band, not an
@@ -38,17 +41,20 @@ Export byte counts differ by 8 B on 5.2.1 (glTF serializer), not a
 gated axis.
 
 `--skip-decimate` skips the LOD DECIMATE stage so LOD1 ratio is 1.0 and
-exit 9 fires. That is the named budget the falsifier violates.
+exit 9 fires. `--lift-z` raises the finished mesh 0.05 m so the grounded
+budget fails and exit 16 fires. Those are the named budgets the two
+falsifiers violate.
 
 ## Run
 
 ```bash
 blender --background --python cart.py --
 blender --background --python cart.py -- --skip-decimate
+blender --background --python cart.py -- --lift-z
 blender --background --python cart.py -- --output cart.png
 ```
 
-Smoke does not pass `--output` or `--skip-decimate`.
+Smoke does not pass `--output`, `--skip-decimate`, or `--lift-z`.
 
 ## Exit codes
 
@@ -72,3 +78,6 @@ File-local. `9` is a valid check code. `10` is reserved for
 | 12 | Bake did not finish or image has no data |
 | 13 | Export file missing or empty |
 | 14 | `--output` produced no file |
+| 15 | Hygiene: loose geometry, non-manifold, zero-area, doubles, or n-gons |
+| 16 | Bbox min Z not grounded (`--lift-z` lands here) |
+| 17 | Material-island gap above tolerance (parts meant to touch) |