fix(showcase): terrain-scatter and park-bench visual quality pass

docs/gallery/index.html

@@ -964,12 +964,12 @@ <h2><a href="treasure-chest/">treasure-chest</a></h2>
       </article>
       <article class="card" data-tags="mesh export showcase">
         <a class="card-media" href="terrain-scatter/" aria-label="terrain-scatter example detail page">
-          <img src="assets/terrain-scatter-hero.webp" alt="terrain-scatter — A Geometry Nodes hill tile with masonry scatter through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than an API contract." loading="lazy" decoding="async" />
+          <img src="assets/terrain-scatter-hero.webp" alt="terrain-scatter — A Geometry Nodes hill tile with seated icosphere scatter through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than an API…" loading="lazy" decoding="async" />
         </a>
         <div class="card-body">
           <h2><a href="terrain-scatter/">terrain-scatter</a></h2>
-          <p class="teaches">A Geometry Nodes hill tile with masonry scatter 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: 1194 tris, two materials with 486 stone faces, UVs in 0..1 with zero AABB overlap, outer AABB 1.800×1.800×0.655 m, LOD ratios in band, convex collider 52 tris, non-empty glTF. --skip-decimate exits 9 on the LOD1 ratio budget.</p>
+          <p class="teaches">A Geometry Nodes hill tile with seated icosphere scatter 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: 1758 tris, two materials with 720 stone faces, UVs in 0..1 with zero AABB overlap, outer AABB 1.800×1.800×0.552 m, grounded zmin, 9 stones of ≥80 faces seated on sampled dirt Z (offset −35 mm, floor zmin 0.113 m), LOD ratios in band, convex collider 81 tris, hygiene zero, non-empty glTF. --skip-decimate exits 9; --stray-vert 15; --lift-z 16; --poke-rock 17; --float-rocks 18; --box-rocks 19.</p>
           <a class="card-link" href="terrain-scatter/">View example <span aria-hidden="true">&rarr;</span></a>
         </div>
       </article>
@@ -1008,12 +1008,12 @@ <h2><a href="cart/">cart</a></h2>
       </article>
       <article class="card" data-tags="mesh export showcase">
         <a class="card-media" href="park-bench/" aria-label="park-bench example detail page">
-          <img src="assets/park-bench-hero.webp" alt="park-bench — A procedural wrought-iron park bench through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than an API contract." loading="lazy" decoding="async" />
+          <img src="assets/park-bench-hero.webp" alt="park-bench — A procedural wrought-iron park bench with tangent tube scroll feet through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than…" loading="lazy" decoding="async" />
         </a>
         <div class="card-body">
           <h2><a href="park-bench/">park-bench</a></h2>
-          <p class="teaches">A procedural wrought-iron park bench 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: 2100 tris, two materials with 510 metal faces, UVs in 0..1 with zero AABB overlap, outer AABB 1.080×0.566×0.853 m, LOD ratios in band (5.2 COLLAPSE more aggressive on LOD2), convex collider 106 tris, non-empty glTF. --skip-decimate exits 9 on the LOD1 ratio budget.</p>
+          <p class="teaches">A procedural wrought-iron park bench with tangent tube scroll feet 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: 2520 tris, two materials with 540 metal and 756 wood faces, UVs in 0..1 with zero AABB overlap, outer AABB 1.295×0.632×0.884 m, grounded zmin, 4 named toes, stretcher gap 1.2 mm, slat gap 0.3 mm, seat span 1.272 m, LOD ratios in band, convex collider 82 tris, hygiene zero, non-empty glTF. --skip-decimate exits 9; --stray-vert 15; --lift-z/--short-feet 16; --float-stretcher 17; --gap-slats 18; --narrow-seat 19.</p>
           <a class="card-link" href="park-bench/">View example <span aria-hidden="true">&rarr;</span></a>
         </div>
       </article>

showcase/README.md

@@ -89,6 +89,13 @@ entry in `showcase/gallery.json`, and a rendered still.
   vertices as inner ones the moment the host is out of round, which is
   how a hoop that visibly gapped on one side still passed. The paired
   falsifier makes the wrapper a true circle on an out-of-round host.
+- **Sampled host seat (exit 17/18 on scatter).** Instanced scatter
+  seats by sampling the host surface Z at each instance's XY, biting a
+  named depth, then clamping instance verts above the slab floor. A
+  closed-form icosphere (or equivalent) replaces the GN cube so the
+  scatter is stones, not open crates; a per-shell face floor is the
+  budget that catches a cube leftover (exit 19). `--poke-rock` skips
+  the clamp and over-bites; `--float-rocks` seats above the host.
 - **Plumb and real-world size (exit 19).** Assert that the axis of a
   turned or lofted body is vertical, by comparing the XY centroid of a
   bottom slab against a top slab — not the exact `zmin` and `zmax`

showcase/gallery.json

@@ -92,8 +92,8 @@
     {
       "name": "terrain-scatter",
       "dir": "showcase/terrain-scatter",
-      "teaches": "A Geometry Nodes hill tile with masonry scatter through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than an API contract.",
-      "witnessesFix": "Recomputed: 1194 tris, two materials with 486 stone faces, UVs in 0..1 with zero AABB overlap, outer AABB 1.800×1.800×0.655 m, LOD ratios in band, convex collider 52 tris, non-empty glTF. --skip-decimate exits 9 on the LOD1 ratio budget.",
+      "teaches": "A Geometry Nodes hill tile with seated icosphere scatter through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than an API contract.",
+      "witnessesFix": "Recomputed: 1758 tris, two materials with 720 stone faces, UVs in 0..1 with zero AABB overlap, outer AABB 1.800×1.800×0.552 m, grounded zmin, 9 stones of ≥80 faces seated on sampled dirt Z (offset −35 mm, floor zmin 0.113 m), LOD ratios in band, convex collider 81 tris, hygiene zero, non-empty glTF. --skip-decimate exits 9; --stray-vert 15; --lift-z 16; --poke-rock 17; --float-rocks 18; --box-rocks 19.",
       "hero": "docs/gallery/assets/terrain-scatter-hero.webp",
       "preview": "showcase/terrain-scatter/preview.webp",
       "tags": [
@@ -140,8 +140,8 @@
     {
       "name": "park-bench",
       "dir": "showcase/park-bench",
-      "teaches": "A procedural wrought-iron park bench through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than an API contract.",
-      "witnessesFix": "Recomputed: 2100 tris, two materials with 510 metal faces, UVs in 0..1 with zero AABB overlap, outer AABB 1.080×0.566×0.853 m, LOD ratios in band (5.2 COLLAPSE more aggressive on LOD2), convex collider 106 tris, non-empty glTF. --skip-decimate exits 9 on the LOD1 ratio budget.",
+      "teaches": "A procedural wrought-iron park bench with tangent tube scroll feet through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than an API contract.",
+      "witnessesFix": "Recomputed: 2520 tris, two materials with 540 metal and 756 wood faces, UVs in 0..1 with zero AABB overlap, outer AABB 1.295×0.632×0.884 m, grounded zmin, 4 named toes, stretcher gap 1.2 mm, slat gap 0.3 mm, seat span 1.272 m, LOD ratios in band, convex collider 82 tris, hygiene zero, non-empty glTF. --skip-decimate exits 9; --stray-vert 15; --lift-z/--short-feet 16; --float-stretcher 17; --gap-slats 18; --narrow-seat 19.",
       "hero": "docs/gallery/assets/park-bench-hero.webp",
       "preview": "showcase/park-bench/preview.webp",
       "tags": [

showcase/park-bench/README.md

@@ -1,9 +1,16 @@
 # Park bench
 
 A showcase piece, not an example. Procedural wrought-iron park bench
-(scrolled legs, slatted seat and back, armrests) then the shipped
-pipeline: unique-cell UVs, Cycles high-to-low normal bake, LOD chain,
-convex collider, Unity glTF export.
+(quarter-circle tube scroll feet tangent to the posts, slatted seat and
+back, arm scrolls, wood arm caps) then the shipped pipeline: unique-cell
+UVs, Cycles high-to-low normal bake, LOD chain, convex collider, Unity
+glTF export.
+
+Posts, feet, stretchers and arms share named stations (`hx`, `hy`,
+`SEAT_Z`, `ARM_Z`, `SCROLL_R`). A foot is a 6-gon tube about
+`(hy ± R, R)` so it is tangent to the post at `z=R` and plants at `z=0`.
+The H-stretcher meets the posts at those stations; slats insert into the
+post volume without sharing corner verts with the seat rails.
 
 It asserts **budget conformance** of the generated result. It does not
 witness an API contract. "It rendered without error" is not a check.
@@ -13,6 +20,11 @@ witness an API contract. "It rendered without error" is not a check.
 `bake_normal_high_to_low.py`, `setup_bake_target_image.py`,
 `lod_chain.py` / `decimate_to_budget.py`, `convex_hull_collider.py`,
 `export_preset_unity.py` (helpers copied, not imported as a package).
+Hygiene combinatorics match `examples/mesh-hygiene-audit` (copied, not
+imported).
+
+Intended size: 1.40 m sitting width, 0.50 m seat depth, 0.43 m seat
+height, 0.64 m arm height; outer AABB 1.295 × 0.632 × 0.884 m.
 
 ## Budgets
 
@@ -21,39 +33,89 @@ materials, UVs, evaluated LOD, collider, or export file.
 
 | Axis | Declared | Measured (4.5.11 / 5.1.2 / 5.2.1) |
 | --- | --- | --- |
-| Base triangles | 2000–2200 | 2100 / 2100 / 2100 |
-| LOD1 ratio | 0.32–0.62 of base | 0.5000 / 0.5000 / 0.4952 |
-| LOD2 ratio | 0.10–0.35 of base | 0.2200 / 0.2200 / 0.1400 |
-| Materials | exactly 2 distinct, ≥48 metal faces | 2 slots, 510 metal |
+| Base triangles | 2200–4200 | 2520 / 2520 / 2520 |
+| LOD1 ratio | 0.32–0.62 of base | 0.5000 / 0.5000 / 0.5000 |
+| LOD2 ratio | 0.10–0.35 of base | 0.2198 / 0.2198 / 0.2198 |
+| Materials | exactly 2 distinct, ≥48 metal, ≥24 wood | 2 slots, 540 metal / 756 wood |
 | UVs | in `0..1`, AABB overlap ≤ 1e-5 | in range, overlap 0 |
-| Outer AABB | (1.080, 0.566, 0.853) m ± 0.01 | (1.0800, 0.5657, 0.8531), zmin 0 |
-| Collider tris | ≤ 140 | 106 |
-| Export | written, size > 0 | 159868 / 159868 / 159852 bytes |
+| Outer AABB | (1.295, 0.632, 0.884) m ± 0.015 | (1.2945, 0.6314, 0.8840), zmin 0 |
+| Collider tris | ≤ 180 | 82 |
+| Export | written, size > 0 | 188164 / 188164 / 188148 bytes |
+
+Base triangles rose from **2100 to 2520** in the quality pass: box-segment
+scrolls became 6-gon tubes. Outer AABB widened from 1.080 × 0.566 × 0.853 m
+to a 1.40 m sitting-width bench.
+
+DECIMATE COLLAPSE triangle counts are **not** guaranteed identical across
+series — the gate is a ratio band, not an exact count. This mesh matched
+on 4.5.11 / 5.1.2 / 5.2.1. Bake pixels are stochastic; the gate is
+`has_data` plus operator `FINISHED`, not byte-identity. Construction uses
+no RNG. Export byte counts differ by 16 B on 5.2.1 (glTF serializer), not
+a gated axis.
+
+### Hygiene
+
+Recomputed from the generated mesh, not asserted about the script.
+
+| Axis | Declared | Measured (all three) |
+| --- | --- | --- |
+| Non-manifold edges | 0 | 0 |
+| Loose verts / edges | 0 / 0 | 0 / 0 |
+| Doubles merged at 1e-5 | 0 | 0 |
+| Zero-area faces | 0 | 0 |
+| N-gons | 0 | 0 |
+| Coplanar disjoint face pairs | 0 | 0 |
+| Grounded: `zmin` | within 1e-4 of 0 | 0.0000 |
+| Named toes | 4, each `zmin` ≤ 0.002 | 4, 0.00000 |
+
+### Joint fit and seat
+
+| Axis | Declared | Measured (all three) |
+| --- | --- | --- |
+| Stretcher-to-post BVH gap | ≤ 0.008 m | 0.00120 |
+| Slat-to-post BVH gap | ≤ 0.008 m | 0.00028 |
+| Seat span vs `2·hx` | ± 0.08 m | 1.2720 vs 1.260 |
 
-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
-exact count. Bake pixels are stochastic; the gate is `has_data` plus
-operator `FINISHED`, not byte-identity. Construction uses no RNG.
-Export byte counts differ by 16 B on 5.2.1 (glTF serializer), not a
-gated axis.
+### Falsifiers
+
+Each violates one named budget. All were run on 4.5.11, 5.1.2 and 5.2.1
+and returned the same code on each.
+
+| Flag | Budget violated | Exit |
+| --- | --- | --- |
+| `--skip-decimate` | LOD1 ratio band | 9 |
+| `--stray-vert` | loose vertex count is 0 | 15 |
+| `--lift-z` | bounding box `zmin` is 0 | 16 |
+| `--short-feet` | named toes plant at z=0 | 16 |
+| `--float-stretcher` | stretcher-to-post BVH gap | 17 |
+| `--gap-slats` | slat-to-post BVH gap | 18 |
+| `--narrow-seat` | seat span vs `2·hx` | 19 |
 
-`--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.
+`--short-feet` lifts only the outward toe verts. After recenter the post
+join is the AABB `zmin`, so the AABB gate would still pass; the named-toe
+stations fail.
 
 ## Run
 
 ```bash
 blender --background --python park_bench.py --
 blender --background --python park_bench.py -- --skip-decimate
+blender --background --python park_bench.py -- --stray-vert
+blender --background --python park_bench.py -- --lift-z
+blender --background --python park_bench.py -- --short-feet
+blender --background --python park_bench.py -- --float-stretcher
+blender --background --python park_bench.py -- --gap-slats
+blender --background --python park_bench.py -- --narrow-seat
 blender --background --python park_bench.py -- --output bench.png
 ```
 
-Smoke does not pass `--output` or `--skip-decimate`.
+Smoke passes no flags.
 
 ## Exit codes
 
 File-local. `9` is a valid check code. `10` is reserved for
-`gallery_framing.check_framing` on the `--output` path.
+`gallery_framing.check_framing` on the `--output` path. `15`–`19` are the
+hygiene and joint-fit family.
 
 | Code | Meaning |
 | --- | --- |
@@ -72,3 +134,8 @@ 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 (`--stray-vert` lands here) |
+| 16 | Grounded zmin / named toes (`--lift-z`, `--short-feet`) |
+| 17 | Stretcher-to-post gap (`--float-stretcher`) |
+| 18 | Slat-to-post gap (`--gap-slats`) |
+| 19 | Seat span (`--narrow-seat`) |