TMHSDigital · TMHSDigital · Sep 16, 2026 · Sep 16, 2026 · Sep 16, 2026
@@ -1096,12 +1096,12 @@ <h2><a href="signpost/">signpost</a></h2>
       </article>
       <article class="card" data-tags="mesh export showcase">
         <a class="card-media" href="chopping-block/" aria-label="chopping-block example detail page">
-          <img src="assets/chopping-block-hero.webp" alt="chopping-block — A procedural chopping block with an embedded axe through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than an API contract." loading="lazy" decoding="async" />
+          <img src="assets/chopping-block-hero.webp" alt="chopping-block — A procedural log-round chopping block with an iron hoop and a felling axe buried in the sawn face, through UVs, bake, LOD, collider, and Unity glTF, asserting…" loading="lazy" decoding="async" />
         </a>
         <div class="card-body">
           <h2><a href="chopping-block/">chopping-block</a></h2>
-          <p class="teaches">A procedural chopping block with an embedded axe 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: 2016 tris, two materials with 122 metal faces, UVs in 0..1 with zero AABB overlap, outer AABB 0.471×0.463×0.841 m, LOD ratios in band (5.2 COLLAPSE 2 tris leaner on LOD2), convex collider 188 tris, non-empty glTF. --skip-decimate exits 9 on the LOD1 ratio budget.</p>
+          <p class="teaches">A procedural log-round chopping block with an iron hoop and a felling axe buried in the sawn face, 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: 1472 tris, three materials with 252 bark / 252 grain / 288 metal faces, UVs in 0..1 with zero AABB overlap, outer AABB 0.526 x 0.526 x 1.012 m, LOD ratios in band, convex collider 434 tris, non-empty glTF. Hygiene: zero non-manifold edges, loose geometry, doubles, zero-area faces, n-gons and coplanar disjoint face pairs, grounded at zmin 0, log plumb to 1e-7. Joint fit: four shells, 18.0 mm haft clearance in the eye, 78.7 mm bit bury, hoop biting 3.7-4.0 mm into the log on every segment. --fat-haft exits 17 on eye clearance; --round-band exits 18 on the hoop bite band.</p>
           <a class="card-link" href="chopping-block/">View example <span aria-hidden="true">&rarr;</span></a>
         </div>
       </article>

@@ -37,16 +37,22 @@ entry in `showcase/gallery.json`, and a rendered still.
   falsifier (exit 9), `--stray-vert` the mesh-hygiene falsifier (exit
   15), `--lift-z` the grounded-zmin falsifier (exit 16), and
   `--fat-rungs` (or the piece's equivalent) the joint-fit falsifier
-  (exit 17). A budget with no falsifier witnesses nothing: prove each
-  one fails once, and check the exit code, not just non-zero.
+  (exit 17), and `--round-band` (or equivalent) the seat-conformance
+  falsifier (exit 18). A budget with no falsifier witnesses nothing:
+  prove each one fails once, and check the exit code, not just
+  non-zero.
 - **Hygiene budgets.** Copied combinatorics from
   `examples/mesh-hygiene-audit` (do not import the example). Every piece
   asserts on the generated mesh: non-manifold edges 0, loose verts 0,
   loose edges 0, doubles at 1e-5 0, zero-area faces 0, n-gons 0, world
-  AABB min Z within 1e-4 of 0. Multi-body props do **not** require Euler
-  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).
+  AABB min Z within 1e-4 of 0, and coplanar disjoint face pairs 0. Count
+  the last one over faces that share **no** vertex: the triangles of one
+  flat fan cap are coplanar and close-centred by construction, and
+  counting those makes the budget unsatisfiable rather than meaningful.
+  Multi-body props do **not** require Euler 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).
 - **Joint-fit budgets.** Parts that interpenetrate on purpose — a tenon
   in a mortise, a peg in a hub — assert how deep the overlap goes, not
   just that it exists. Split the mesh into shells by edge connectivity,
@@ -58,6 +64,25 @@ entry in `showcase/gallery.json`, and a rendered still.
   the host's chamfer as a spike — that is the class this catches.
   Measure in the construction frame (un-rotate by any rake) so a tilted
   host does not inflate its own AABB.
+- **Seat conformance (exit 18).** A band, hoop, strap or collar wrapped
+  around a host asserts a **banded** seat depth — a minimum so it cannot
+  float and a maximum so it cannot sink — sampled per angular segment
+  rather than as a single global figure. Derive the wrapper's profile
+  from the host's own radius function instead of a circle, and classify
+  inner versus outer vertices against the host surface at each vertex's
+  own angle. A global midpoint radius misclassifies outer chamfer
+  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.
+- **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`
+  rings, which may be a handful of vertices once a rim is notched or
+  chipped. Separately assert the body's own diameter and height against
+  the dimensions the README states in metres, with a named tolerance.
+  The outer AABB does not cover this: on a prop with an appendage the
+  AABB is the appendage, and the body can drift to any size underneath
+  it.
 - **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:
@@ -67,7 +92,14 @@ entry in `showcase/gallery.json`, and a rendered still.
   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.
+  named check. `15`–`19` are reserved across pieces for the hygiene
+  family above: `15` hygiene, `16` grounded, `17` joint fit, `18` seat
+  conformance and contact, `19` plumb and real-world size.
+- **Shading is part of the model.** A flat-shaded low-poly body and a
+  smooth-shaded one are different objects to a viewer. Smoothing a
+  wobbled 36-gon erases every bit of surface modelling in it and leaves
+  a featureless drum, so decide per part and say why. Nothing here is
+  measurable, which is exactly why it has to be looked at.
 - **Rendered still and gallery entry.** Showcase pieces are visual by
   definition. The pathology / sidecar exemption does not apply. Call
   `examples/gallery_framing.check_framing` on the `--output` path only.

@@ -1,9 +1,16 @@
 # Chopping block
 
-A showcase piece, not an example. Procedural chopping block (hooped
-timber stump with an embedded axe) then the shipped pipeline:
-unique-cell UVs, Cycles high-to-low normal bake, LOD chain, convex
-collider, Unity glTF export.
+A showcase piece, not an example. Procedural chopping block (a hooped
+log round with a felling axe buried in the sawn face) then the shipped
+pipeline: unique-cell UVs, Cycles high-to-low normal bake, LOD chain,
+convex collider, Unity glTF export.
+
+The log is an out-of-round loft whose radius is a closed-form function
+of angle and height; the hoop, the top rim and the drying checks are all
+generated from that same function, so they stay seated when a dimension
+changes. The axe head is one lofted shell from poll to bit with its
+chamfers modelled into the section profile, and the haft is swept
+through the eye rather than pushed into it.
 
 It asserts **budget conformance** of the generated result. It does not
 witness an API contract. "It rendered without error" is not a check.
@@ -21,38 +28,89 @@ materials, UVs, evaluated LOD, collider, or export file.
 
 | Axis | Declared | Measured (4.5.11 / 5.1.2 / 5.2.1) |
 | --- | --- | --- |
-| Base triangles | 1880–2160 | 2016 / 2016 / 2016 |
+| Base triangles | 1410–1530 | 1472 / 1472 / 1472 |
 | LOD1 ratio | 0.32–0.62 of base | 0.5000 / 0.5000 / 0.5000 |
-| LOD2 ratio | 0.10–0.35 of base | 0.2192 / 0.2192 / 0.2183 |
-| Materials | exactly 2 distinct, ≥24 metal faces | 2 slots, 122 metal |
+| LOD2 ratio | 0.10–0.35 of base | 0.2188 / 0.2188 / 0.2188 |
+| Materials | exactly 3 distinct; ≥160 bark, ≥90 grain, ≥24 metal faces | 3 slots; 252 / 252 / 288 |
 | UVs | in `0..1`, AABB overlap ≤ 1e-5 | in range, overlap 0 |
-| Outer AABB | (0.471, 0.463, 0.841) m ± 0.01 | (0.4713, 0.4626, 0.8413), zmin 0 |
-| Collider tris | ≤ 220 | 188 |
-| Export | written, size > 0 | 157000 / 157000 / 156992 bytes |
+| Outer AABB | (0.526, 0.526, 1.012) m ± 0.01 | (0.5264, 0.5264, 1.0117) |
+| Collider tris | ≤ 470 | 434 |
+| Export | written, size > 0 | 150784 / 150784 / 150776 bytes |
+
+### Hygiene
 
-DECIMATE COLLAPSE triangle counts are **not** identical across series —
-5.2.1 is 2 tris leaner 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 8 B on 5.2.1 (glTF serializer), not a gated axis.
+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-5 of 0 | 0.0000 |
+| Log axis out of plumb | ≤ 2e-4 | 0.0000000 |
+| Log size | 0.535 × 0.360 m ± 0.03 / ± 0.02 | 0.5464 × 0.3600 |
 
-`--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.
+### Joint fit
+
+Four shells that have to meet correctly: log, hoop, head, haft.
+
+| Axis | Declared | Measured (all three) |
+| --- | --- | --- |
+| Shell count | exactly 4 | 4 |
+| Haft clearance inside the eye | ≥ 0.006 m | 0.01800 |
+| Haft engagement through the eye | ≥ 0.020 m | 0.08049 |
+| Haft breakout margin below the head | ≥ 0.006 m | 0.02351 |
+| Bit bury below the sawn top | ≥ 0.030 m | 0.07871 |
+| Bit inset from the rim | ≥ 0.030 m | 0.14647 |
+| Hoop bite into the log, every segment | 0.002–0.007 m | 0.00371–0.00400 |
+| Haft clearance above the log | ≥ 0.015 m, 0 verts inside | 0.07858, 0 |
+
+The hoop bite is binned by angular segment against the log's own radius
+function. A single global midpoint radius misclassifies outer chamfer
+vertices as inner ones on an out-of-round log, which is how a hoop that
+visibly floated on one side still passed.
+
+DECIMATE COLLAPSE triangle counts happen to agree across all three
+series here; the gate is still 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 8 B on 5.2.1 (glTF serializer), not a gated axis.
+
+### Falsifiers
+
+Each violates one named budget. All five 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 |
+| `--fat-haft` | haft clearance inside the eye | 17 |
+| `--round-band` | hoop bite into the log | 18 |
 
 ## Run
 
 ```bash
 blender --background --python chopping_block.py --
 blender --background --python chopping_block.py -- --skip-decimate
+blender --background --python chopping_block.py -- --stray-vert
+blender --background --python chopping_block.py -- --lift-z
+blender --background --python chopping_block.py -- --fat-haft
+blender --background --python chopping_block.py -- --round-band
 blender --background --python chopping_block.py -- --output chopping-block.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 |
 | --- | --- |
@@ -61,7 +119,7 @@ File-local. `9` is a valid check code. `10` is reserved for
 | 2 | argparse / usage |
 | 3 | Mesh did not build / no UV layer |
 | 4 | Base triangle count outside range |
-| 5 | Material count ≠ 2 distinct slots, or wood/metal faces missing |
+| 5 | Material count ≠ 3 distinct slots, or a face-count floor missed |
 | 6 | UVs outside 0..1 |
 | 7 | UV AABB overlap above tolerance |
 | 8 | World AABB off declared outer size |
@@ -71,3 +129,8 @@ 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 | Mesh hygiene: loose, non-manifold, zero-area, doubles, n-gons, z-fight |
+| 16 | Not grounded: bounding box `zmin` off 0 |
+| 17 | Axe joint fit: shell count, eye clearance, engagement, breakout, bury, inset |
+| 18 | Contact fit: hoop bite band, or haft fouling the log |
+| 19 | Log out of plumb, or off its stated real-world size |