@@ -1058,12 +1058,12 @@ <h2><a href="anvil/">anvil</a></h2>
       </article>
       <article class="card" data-tags="mesh export showcase">
         <a class="card-media" href="water-trough/" tabindex="-1" aria-hidden="true">
-          <img src="assets/water-trough-hero.webp" alt="A staved wooden water trough with solid half-round end boards on crossed trestle legs, half full of dark water." loading="lazy" decoding="async" />
+          <img src="assets/water-trough-hero.webp" alt="A staved wooden water trough with half-round ends built of three boards, on crossed trestle legs, half full of dark water." loading="lazy" decoding="async" />
         </a>
         <div class="card-body">
           <h2><a href="water-trough/">water-trough</a></h2>
           <p class="teaches">A procedural watertight water trough 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: 3700 tris, three materials with 1674 wood, 156 metal and 29 water faces, UVs in 0..1 with zero AABB overlap, outer AABB 1.093×0.552×0.504 m, zmin 0, four shoes planted, U end-cap rim span 5 mm, strap BVH gap 0, water-hull gap 2.6 mm, hull 1.045×0.466 m, LOD ratios in band, convex collider 64 tris, non-empty glTF. --skip-decimate exits 9; --stray-vert 15; --lift-z/--short-legs 16; --box-ends 17; --float-strap 18; --narrow-hull 19.</p>
+          <p class="witnesses"><span class="tag">witnesses</span> Recomputed: 3316 tris, three materials with 1482 wood, 156 metal and 29 water faces, UVs in 0..1 with zero AABB overlap, outer AABB 1.093x0.552x0.5055 m, zmin 0, four shoes planted, each end three lapped boards, end rim span 21 mm, strap BVH gap 0, water-hull gap 2.6 mm, water contained on 66 of 66 rays, hull 1.045x0.466 m, LOD ratios in band, convex collider 68 tris, non-empty glTF. --skip-decimate exits 9; --stray-vert 15; --lift-z/--short-legs 16; --box-ends 17; --float-strap/--open-ends 18; --narrow-hull 19; --slab-ends 20.</p>
           <a class="card-link" href="water-trough/">View showcase piece<span class="sr-only"> water-trough</span> <span aria-hidden="true">&rarr;</span></a>
         </div>
       </article>
 
@@ -458,6 +458,14 @@ entry in `showcase/gallery.json`, and a rendered still.
   not by a radius: a quarter of the head's width is smaller than any
   "round" test built for the whole disk. `--one-piece-head` /
   `--one-piece-bottom` are the falsifiers.
+
+  The same holds for any end that closes a vessel. `water-trough`'s ends
+  were one D-shaped slab each; they are three vertical boards. Where the
+  boards must also hold water, lap them a millimetre into each other
+  rather than leaving a seam: a through gap leaks, and lets a containment
+  ray through, while the bevel on the boards' face edges still shows the
+  joint. Read any rim test on the union of an end's boards, or a board's
+  inner edge at a joint is taken for the rim (`--slab-ends`).
 - **Rope is laid, not piped.** A smooth tube with a rope material is a
   plastic hose. Loft a three-lobed section and turn it one vertex step per
   ring, so each lobe winds along the path as a strand. That costs the same
 
@@ -195,8 +195,8 @@
       "name": "water-trough",
       "dir": "showcase/water-trough",
       "teaches": "A procedural watertight water trough through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than an API contract.",
-      "alt": "A staved wooden water trough with solid half-round end boards on crossed trestle legs, half full of dark water.",
-      "witnessesFix": "Recomputed: 3700 tris, three materials with 1674 wood, 156 metal and 29 water faces, UVs in 0..1 with zero AABB overlap, outer AABB 1.093×0.552×0.504 m, zmin 0, four shoes planted, U end-cap rim span 5 mm, strap BVH gap 0, water-hull gap 2.6 mm, hull 1.045×0.466 m, LOD ratios in band, convex collider 64 tris, non-empty glTF. --skip-decimate exits 9; --stray-vert 15; --lift-z/--short-legs 16; --box-ends 17; --float-strap 18; --narrow-hull 19.",
+      "alt": "A staved wooden water trough with half-round ends built of three boards, on crossed trestle legs, half full of dark water.",
+      "witnessesFix": "Recomputed: 3316 tris, three materials with 1482 wood, 156 metal and 29 water faces, UVs in 0..1 with zero AABB overlap, outer AABB 1.093x0.552x0.5055 m, zmin 0, four shoes planted, each end three lapped boards, end rim span 21 mm, strap BVH gap 0, water-hull gap 2.6 mm, water contained on 66 of 66 rays, hull 1.045x0.466 m, LOD ratios in band, convex collider 68 tris, non-empty glTF. --skip-decimate exits 9; --stray-vert 15; --lift-z/--short-legs 16; --box-ends 17; --float-strap/--open-ends 18; --narrow-hull 19; --slab-ends 20.",
       "hero": "docs/gallery/assets/water-trough-hero.webp",
       "preview": "showcase/water-trough/preview.webp",
       "tags": [
 
@@ -1,13 +1,13 @@
 # Water trough
 
 A showcase piece, not an example. Procedural staved water trough on a
-timber stand (watertight U-hull, solid end boards, contained water, iron
+timber stand (watertight U-hull, board-built ends, contained water, iron
 straps, trestle legs) then the shipped pipeline: unique-cell UVs, Cycles
 high-to-low normal bake, LOD chain, convex collider, Unity glTF export.
 
 The hull, ends, straps and water all sample the same YZ arc. Each end
-is a solid board whose bottom follows the hull's outer arc and whose top
-is level, and the staves tenon into it. It is neither a bounding-box slab
+is three vertical boards whose bottoms follow the hull's outer arc and
+whose tops are level, and the staves tenon into them. It is neither a bounding-box slab
 around the U (`--box-ends`) nor an open U-band (`--open-ends`). Straps sit at `STRAP_X`, offset from `LEG_X`, so the trestle does not
 punch through the iron. Stretchers span the inner faces of the legs.
 `--round-band` is not used; `--float-strap` is the seat falsifier.
@@ -33,20 +33,21 @@ materials, UVs, evaluated LOD, collider, or export file.
 
 | Axis | Declared | Measured (4.5.11 / 5.1.2 / 5.2.1) |
 | --- | --- | --- |
-| Base triangles | 2800–3500 | 3124 / 3124 / 3124 |
+| Base triangles | 2800–3500 | 3316 / 3316 / 3316 |
 | LOD1 ratio | 0.32–0.62 of base | 0.5000 / 0.5000 / 0.5000 |
-| LOD2 ratio | 0.10–0.35 of base | 0.2200 / 0.2200 / 0.2200 |
-| Materials | exactly 3 distinct; ≥24 wood, ≥24 metal, ≥6 water | 3 slots; 1386 / 156 / 29 |
+| LOD2 ratio | 0.10–0.35 of base | 0.2195 / 0.2195 / 0.2195 |
+| Materials | exactly 3 distinct; ≥24 wood, ≥24 metal, ≥6 water | 3 slots; 1482 / 156 / 29 |
 | UVs | in `0..1`, AABB overlap ≤ 1e-5 | in range, overlap 0 |
 | Outer AABB | (1.093, 0.552, 0.5055) m ± 0.01 | (1.0932, 0.5520, 0.5055), zmin 0 |
-| Collider tris | ≤ 80 | 64 |
-| Export | written, size > 0 | 228520 / 228520 / 228504 bytes |
+| Collider tris | ≤ 80 | 68 |
+| Export | written, size > 0 | 242240 / 242240 / 242224 bytes |
 
 Base triangles rose from **2484 to 3700** in the first quality pass: box
 end slabs and a single extruded U became ten jittered staves, U end-caps,
 continuous straps offset from the legs, and stretchers that meet the
 inner faces. The second pass took them to **3124**: the open U-band ends
-became solid end boards, which close the section with fewer faces.
+became solid end boards, which close the section with fewer faces. The
+third pass took them to **3316**: each end became three boards.
 
 DECIMATE COLLAPSE triangle counts are **not** identical across series —
 the gate is a ratio band, not an exact count. Bake pixels are
@@ -79,10 +80,11 @@ Recomputed from the generated mesh, not asserted about the script.
 
 | Axis | Declared | Measured (all three) |
 | --- | --- | --- |
-| End-cap rim Z-span | ≤ 0.080 m | 0.0050 |
+| End-cap rim Z-span (union of an end's boards) | ≤ 0.080 m | 0.0208 |
 | Strap-to-hull BVH gap | ≤ 0.008 m | 0.00000 |
 | Water-to-hull BVH gap | ≤ 0.008 m | 0.00260 |
 | Water contained by the end boards | 0 misses over 66 outward rays | 0 of 66 |
+| **End boards** per end | ≥ 3 | 3 |
 
 ### Why the ends are solid boards
 
@@ -101,6 +103,23 @@ tested and not only the rim a band would cover. Every ray must hit
 timber within `1.5 × END_T`. `--open-ends` restores the U-bands: all 66
 rays miss, and the piece exits 18.
 
+### Why each end is three boards
+
+The third pass found each end was one D-shaped slab: a single board
+from rim to rim, one tone, no joint, the thing the showcase's "a head or
+bottom is boards, not a slab" rule exists to prevent (end orthos,
+end-cap close-ups, the hero). Each end is now three vertical boards of
+uneven width (`END_BOARD_FRACS`), each with its own tone and grain, its
+bottom following the hull arc under its own span. Neighbours lap 1 mm
+into each other (`END_BOARD_LAP`), so the joint is tight: a through
+seam would let the water out and a containment ray through, and the
+bevel on each board's face edges shows the joint as a groove. The rim
+span is now read on the union of an end's boards, so the inner edge of
+a board at a joint is not taken for the end's rim. Each board follows
+the arc with three samples (`END_BOARD_SAMPLES`); four cost 3556
+triangles, over the 3500 ceiling. `--slab-ends` restores the one-piece
+board and exits 20.
+
 ### Surface
 
 Staves, boards and legs came out of one flat material, so every board was
@@ -114,10 +133,14 @@ either mirrored as a white sheet or showed nothing, and its spill lifted
 the dark stage. The fill dropped from 68% to 50%, so the inner stave
 walls show above the waterline; at 68% the surface sat nearly flush with
 the rim and read as felt in a frame. Straps widened from 28 to 40 mm.
+The third pass darkened the grazing tint from a pale grey-blue (0.20,
+0.27, 0.29) to a deep teal (0.055, 0.105, 0.115): the hero looks across
+the surface near grazing, where that tint wins, and it read as a
+painted slab.
 
 ### Falsifiers
 
-Each violates one named budget. All eight were run on 4.5.11, 5.1.2 and
+Each violates one named budget. All nine were run on 4.5.11, 5.1.2 and
 5.2.1 and returned the same code on each.
 
 | Flag | Budget violated | Exit |
@@ -130,6 +153,7 @@ Each violates one named budget. All eight were run on 4.5.11, 5.1.2 and
 | `--float-strap` | strap-to-hull gap | 18 |
 | `--narrow-hull` | hull plan vs stated size | 19 |
 | `--open-ends` | water contained by the end boards (restores the open U-band ends) | 18 |
+| `--slab-ends` | end boards per end (restores the one-piece D board; measures 1) | 20 |
 
 `--short-legs` lifts the shoes and stretches each leg's foot down to the
 floor, so AABB `zmin` stays 0 (the legs still plant) and the
@@ -150,6 +174,7 @@ blender --background --python water_trough.py -- --box-ends
 blender --background --python water_trough.py -- --float-strap
 blender --background --python water_trough.py -- --narrow-hull
 blender --background --python water_trough.py -- --open-ends
+blender --background --python water_trough.py -- --slab-ends
 blender --background --python water_trough.py -- --output trough.png
 ```
 
@@ -183,3 +208,4 @@ hygiene and joint-fit family.
 | 17 | Joint fit: end-cap U-rim span (`--box-ends`) |
 | 18 | Seat: strap or water BVH gap (`--float-strap`), or water not contained by the end boards (`--open-ends`) |
 | 19 | Hull length or width off the stated real-world size (`--narrow-hull`) |
+| 20 | An end is fewer than three boards (`--slab-ends`) |