fix(showcase): give hay-bale packed flakes and a stem-mat end instead of felt and gashes

The bale read rough: its straw was a fibre field streaked along the length
like brushed felt, the baked normal cut dark gashes along the top edge, and
the end face baked into horizontal cake layers.

- straw_material: stems lie across the bale in each flake's plane,
  sharpened into distinct stems; a noise-warped saw wave along X cuts the
  flake seams, darkened and grooved into the bump; waxy stems, matte gaps.
- Baked normal at NRM_STRENGTH 0.55. The per-face UV cells the zero-AABB-
  overlap budget requires break the bake's tangent frame at every cell;
  at 1.0 those breaks were the gashes.
- End relief is a product of slow y and z terms instead of sin(z) strata.
  Hull changed: collider 140 -> 100 tris (README table, witnessesFix).

Every budget passes on 5.2.1, 5.1.2 and 4.5.11 (4.5 render path too); all
eight falsifiers keep their exits: --skip-decimate 9, --stray-vert 15,
--lift-z 16, --float-belts 16, --slack-belt 18, --skew-belt 19,
--odd-loaf 19, --low-bake 20. Contact-sheet luma 0.297 (was 0.306; stage
unchanged). Link gate: 122 pages, 0 failures.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: TMHSDigital

README.md

@@ -134,7 +134,7 @@ Budget-conformance props. Not examples. Conventions: [`showcase/README.md`](show
   <a href="showcase/tavern-stool/"><img src="showcase/tavern-stool/preview.webp" width="24%" alt="Tavern stool: a dished round wooden seat holding a pewter tankard, on turned splayed legs with stretchers at two heights and iron ferrules on flat treads, on a dark studio floor" /></a>
   <a href="showcase/iron-cauldron/"><img src="showcase/iron-cauldron/preview.webp" width="24%" alt="Iron cauldron: a round-bellied cast-iron pot hanging by its bail from a timber tripod on a dark studio floor" /></a>
   <a href="showcase/wooden-ladder/"><img src="showcase/wooden-ladder/preview.webp" width="24%" alt="Wooden ladder: an oak ladder with six pale turned hickory rungs through-tenoned into its rails, iron tie-rods under the end rungs and iron shoes, leaning on a barn-board wall with a rope coil on a rung" /></a>
-  <a href="showcase/hay-bale/"><img src="showcase/hay-bale/preview.webp" width="24%" alt="Hay bale: a bound straw bale with two sisal twine belts on a dark studio floor" /></a>
+  <a href="showcase/hay-bale/"><img src="showcase/hay-bale/preview.webp" width="24%" alt="Hay bale: a bound straw bale of packed flakes with two orange twine belts on a dark studio floor" /></a>
   <a href="showcase/crate-stack/"><img src="showcase/crate-stack/preview.webp" width="24%" alt="Crate stack: three slatted shipping crates stacked and yawed, each with iron corner straps and runners, on a dark studio floor" /></a>
   <a href="showcase/stone-archway/"><img src="showcase/stone-archway/preview.webp" width="24%" alt="Stone archway: a semicircular masonry arch with coursed piers, projecting imposts, nine voussoirs and a proud keystone, on a dark studio floor" /></a>
   <a href="showcase/rope-bridge/"><img src="showcase/rope-bridge/preview.webp" width="24%" alt="Rope bridge: a sagging plank deck on foot ropes between two pairs of log posts, with lashed hemp hand ropes, suspenders, and ropes staked to the ground, on a dark studio floor" /></a>
@@ -228,7 +228,7 @@ Budget-conformance props. Not examples. Conventions: [`showcase/README.md`](show
 
 [`wooden-ladder`](showcase/wooden-ladder/) — procedural timber ladder with raked stiles, evenly pitched rungs, and iron shoes through the same pipeline. Falsifiers `--skip-decimate` exits 9, `--drift-rungs` exits 19.
 
-[`hay-bale`](showcase/hay-bale/) — procedural bound hay bale with sisal twine through the same pipeline. Falsifier `--skip-decimate` exits 9.
+[`hay-bale`](showcase/hay-bale/) — procedural bound hay bale with orange polypropylene twine through the same pipeline. Falsifier `--skip-decimate` exits 9.
 
 [`rope-bridge`](showcase/rope-bridge/) — procedural rope footbridge whose plank deck is fitted to a parabola recomputed from the plank tops, with lashed hand ropes and staked foot ropes, through the same pipeline. Falsifiers `--vee-deck` exits 19, `--float-suspenders` exits 18.
 

docs/gallery/assets/hay-bale-hero.webp

@@ -1301,12 +1301,12 @@ <h2><a href="wooden-ladder/">wooden-ladder</a></h2>
       </article>
       <article class="card" data-tags="mesh export showcase" data-kind="showcase" data-category="village" data-name="hay-bale">
         <a class="card-media" href="hay-bale/" tabindex="-1" aria-hidden="true">
-          <img src="assets/hay-bale-hero.webp" alt="A golden fibrous hay bale, square-edged and slightly bulging, bound by two orange twine cords with a small knot loop standing on each." width="1280" height="720" loading="lazy" decoding="async" />
+          <img src="assets/hay-bale-hero.webp" alt="A golden hay bale of packed flakes, its stems and flake seams showing on the flank and a stem mat on the end, bound by two orange twine cords with a small knot loop standing on each." width="1280" height="720" loading="lazy" decoding="async" />
         </a>
         <div class="card-body">
           <h2><a href="hay-bale/">hay-bale</a></h2>
           <p class="teaches">A bound hay bale whose twine belts follow the loaf&#x27;s own raycast cross-section, asserting recomputed geometry budgets, not an API contract.</p>
-          <p class="witnesses"><span class="tag">witnesses</span> Recomputed: 2044 tris, two materials with 1436 hay and 304 twine faces, UVs in 0..1 with zero AABB overlap, outer AABB 0.921x0.508x0.417 m, zmin 0, hygiene and cross-shell z-fight 0, 5 shells, each belt wrapping under the loaf at zmin 1.5 mm, banded belt seat depth 4.0-11.1 mm over 20/20 stations on both belts, belt mirror error 0, cinch depth 10.5 mm, loaf 0.921x0.393 m, 22.4 bake texels per UV cell, LOD ratios in band, convex collider 140 tris, non-empty glTF. --skip-decimate exits 9; --stray-vert 15; --lift-z and --float-belts 16; --slack-belt 18; --skew-belt and --odd-loaf 19; --low-bake 20.</p>
+          <p class="witnesses"><span class="tag">witnesses</span> Recomputed: 2044 tris, two materials with 1436 hay and 304 twine faces, UVs in 0..1 with zero AABB overlap, outer AABB 0.921x0.508x0.417 m, zmin 0, hygiene and cross-shell z-fight 0, 5 shells, each belt wrapping under the loaf at zmin 1.5 mm, banded belt seat depth 4.0-11.1 mm over 20/20 stations on both belts, belt mirror error 0, cinch depth 10.5 mm, loaf 0.921x0.393 m, 22.4 bake texels per UV cell, LOD ratios in band, convex collider 100 tris, non-empty glTF. --skip-decimate exits 9; --stray-vert 15; --lift-z and --float-belts 16; --slack-belt 18; --skew-belt and --odd-loaf 19; --low-bake 20.</p>
           <a class="card-link" href="hay-bale/">View showcase piece<span class="sr-only"> hay-bale</span> <span aria-hidden="true">&rarr;</span></a>
         </div>
       </article>

docs/gallery/contact-sheets/hay-bale-contact-sheet.webp

@@ -365,8 +365,8 @@
       "dir": "showcase/hay-bale",
       "category": "village",
       "teaches": "A bound hay bale whose twine belts follow the loaf's own raycast cross-section, asserting recomputed geometry budgets, not an API contract.",
-      "alt": "A golden fibrous hay bale, square-edged and slightly bulging, bound by two orange twine cords with a small knot loop standing on each.",
-      "witnessesFix": "Recomputed: 2044 tris, two materials with 1436 hay and 304 twine faces, UVs in 0..1 with zero AABB overlap, outer AABB 0.921x0.508x0.417 m, zmin 0, hygiene and cross-shell z-fight 0, 5 shells, each belt wrapping under the loaf at zmin 1.5 mm, banded belt seat depth 4.0-11.1 mm over 20/20 stations on both belts, belt mirror error 0, cinch depth 10.5 mm, loaf 0.921x0.393 m, 22.4 bake texels per UV cell, LOD ratios in band, convex collider 140 tris, non-empty glTF. --skip-decimate exits 9; --stray-vert 15; --lift-z and --float-belts 16; --slack-belt 18; --skew-belt and --odd-loaf 19; --low-bake 20.",
+      "alt": "A golden hay bale of packed flakes, its stems and flake seams showing on the flank and a stem mat on the end, bound by two orange twine cords with a small knot loop standing on each.",
+      "witnessesFix": "Recomputed: 2044 tris, two materials with 1436 hay and 304 twine faces, UVs in 0..1 with zero AABB overlap, outer AABB 0.921x0.508x0.417 m, zmin 0, hygiene and cross-shell z-fight 0, 5 shells, each belt wrapping under the loaf at zmin 1.5 mm, banded belt seat depth 4.0-11.1 mm over 20/20 stations on both belts, belt mirror error 0, cinch depth 10.5 mm, loaf 0.921x0.393 m, 22.4 bake texels per UV cell, LOD ratios in band, convex collider 100 tris, non-empty glTF. --skip-decimate exits 9; --stray-vert 15; --lift-z and --float-belts 16; --slack-belt 18; --skew-belt and --odd-loaf 19; --low-bake 20.",
       "hero": "docs/gallery/assets/hay-bale-hero.webp",
       "preview": "showcase/hay-bale/preview.webp",
       "tags": [

docs/gallery/hay-bale/index.html

@@ -1,7 +1,7 @@
 # Hay bale
 
 A showcase piece, not an example. Procedural bound straw bale (cinched
-pillow loaf, end-grain strata, two orange polypropylene belts that
+pillow loaf, a lumpy stem-mat end, two orange polypropylene belts that
 wrap the loaf's own cross-section, a knot loop standing on each) then the shipped pipeline: unique-cell
 UVs, Cycles high-to-low normal bake, LOD chain, convex collider, Unity
 glTF export.
@@ -65,7 +65,7 @@ RNG and no version-dependent operator.
 | **Cinch depth** | mid-span minus waist in [0.006, 0.020] m | 0.01053 |
 | Loaf X × Z | (0.921, 0.393) m ± 0.02 | (0.9208, 0.3931) |
 | Hay–twine gap | BVH surface < 0.008 m | 0.00009 |
-| Collider tris | ≤ 400 | 140 |
+| Collider tris | ≤ 400 | 100 |
 | Bake texels | smallest UV cell ≥ 12 px at the baked resolution | 22.43 px at 1024 px |
 | Export | written, size > 0 | 203508 / 203508 / 203496 bytes |
 
@@ -181,7 +181,7 @@ the whole bale erased every ridge and nap in it and left a featureless
 pillow that read as a bar of soap. Twine is cord, so the belts and
 hitch loops stay smooth.
 
-The low mesh carries the form — bulge, waist, ridges, end strata — and
+The low mesh carries the form — bulge, waist, ridges, end relief — and
 the **high mesh carries the straw**: `LOAF_CUTS_HIGH` subdivision plus
 per-band flake offsets, moved onto the low mesh by the bake stage. A low
 mesh dense enough to model flakes directly would cost thousands of
@@ -190,15 +190,24 @@ triangles for detail this piece already has a bake for.
 ## Surface
 
 The bale used to read as a wrapped parcel: flat mustard hay, and a wide
-dark band for twine. The hay is now `straw_material`:
-- a dense fibre field stretched along the bale (noise with X compressed),
-  and a weaker crossing field for the strands that lie the other way;
-- colour pulled between pale straw and dark tan by the fibres, with a
-  faint green cast from low-frequency noise;
-- roughness and a bump from the same fibres, so every strand catches
-  light.
-
-The baked normal is chained under that bump (`wire_normal`). The twine
+dark band for twine. Later it read as an upholstered cushion: its fibres
+ran along the length like brushed felt. The hay is now `straw_material`:
+- stems lying *across* the bale, in the plane of each packed flake (noise
+  with Y compressed, a weaker folded set with Z compressed), sharpened by
+  a map range into distinct light and dark stems;
+- flake seams: a saw wave along X at about 2.6 × `FLAKE_W`, warped by
+  noise so the seams wander, darkened and grooved into the bump;
+- colour from dark tan through gold to pale straw, with a faint green cast
+  from low-frequency noise; waxy stems, matte gaps.
+
+It is all object-space, so it runs continuously across the per-face UV
+cells. The baked normal is chained under that bump (`wire_normal`) at
+`NRM_STRENGTH` 0.55. The UV budget (zero per-face AABB overlap) gives every
+face its own cell, so the bake's tangent frame breaks at every cell edge; at
+full strength those breaks cut dark gashes along the top edge. The end face
+used to be `sin(z)` strata, which baked into cake layers gouged across the
+end. It is now a product of slow terms in y and z, which reads as the stem mat of
+the last flake. That changed the hull: the collider went from 140 to 100 tris. The twine
 is a 10 × 14 mm orange polypropylene cord standing 6 mm proud. As an
 8 × 10 mm dark brown cord it stood 4 mm proud of the waisted loaf and read
 as a scored cut in every view. The longitudinal ridge dropped from 14 mm to

docs/gallery/index.html

@@ -648,12 +648,14 @@ def _shape_loaf(verts, flake=False):
         # flared spikes. The ripple is slow (7, not 14) — at 14 it aliased
         # against the subdivision grid and read as a checkerboard quilt.
         if abs(nx) > 0.82:
-            # Strata in Z, not rings in r. A cut bale end shows the flake
-            # layers edge-on; a concentric ripple is not what that looks
-            # like, and at BAKE_RES it resolved into a pixelated bullseye
-            # on the hero that read as a printed target.
+            # The end is the face of the last flake: a mat of stems, lumpy
+            # in both directions. Concentric rings baked into a printed
+            # target; horizontal strata (sin in z alone) baked into cake
+            # layers gouged across the end. A product of slow terms in y and
+            # z reads as packed straw and stays even in x.
             edge = 1.0 - min(1.0, max(abs(ny), abs(nz))) ** 3
-            strata = math.sin((z / BALE_Z) * math.pi * 6.0)
+            strata = (math.sin((z / BALE_Z) * math.pi * 3.0 + 0.7)
+                      * math.cos((y / BALE_Y) * math.pi * 2.4))
             v.co.x += math.copysign(NAP_AMP * strata * edge, x)
 
 
@@ -862,33 +864,68 @@ def _stretched_noise(nt, coord, stretch, scale, detail):
 
 
 def straw_material(name):
-    """Straw: fibres, colour break-up and a fibre bump, not a flat mustard.
-
-    The bale read as a wrapped parcel because its hay was one flat colour
-    with a soft noise. Straw is streaks: a dense fibre field stretched
-    along the bale, a weaker crossing field for the strands that lie the
-    other way, colour pulled between pale straw and dark tan by the fibres,
-    a faint green cast from low-frequency noise, and a bump from the same
-    fibres so every strand catches light.
+    """Straw: stems, flake seams, colour break-up and a bump, not felt.
+
+    Stems lie across the bale in the plane of each packed flake, sharpened
+    into distinct light and dark lines; a warped saw wave along X cuts the
+    seams between flakes, darkened and grooved; colour runs from dark tan
+    through gold to pale straw with a faint green cast from low-frequency
+    noise. All object-space, so it is continuous across the per-face UV
+    cells the bake uses.
     """
     mat = bpy.data.materials.new(name)
     mat.use_nodes = True
     nt = mat.node_tree
     bsdf = nt.nodes["Principled BSDF"]
     coord = nt.nodes.new("ShaderNodeTexCoord")
-    along = _stretched_noise(nt, coord, (0.07, 1.0, 1.0), 110.0, 6.0)
-    across = _stretched_noise(nt, coord, (1.0, 0.09, 1.0), 90.0, 4.0)
+    # Stems lie ACROSS the bale, in the plane of each flake the plunger
+    # packed: long along Y, a weaker folded set along Z. Fibres streaked
+    # along X (the old field) ran with the length like brushed felt, and the
+    # bale read as an upholstered cushion. Sharpened by the map range so each
+    # stem is a crisp light/dark line, not a soft smear.
+    along = _stretched_noise(nt, coord, (1.0, 0.05, 1.0), 150.0, 3.0)
+    across = _stretched_noise(nt, coord, (1.0, 1.0, 0.08), 120.0, 3.0)
     fib = nt.nodes.new("ShaderNodeMix")
     fib.data_type = "FLOAT"
-    _sock(fib.inputs, "Factor_Float").default_value = 0.32
+    _sock(fib.inputs, "Factor_Float").default_value = 0.35
     nt.links.new(along.outputs["Fac"], _sock(fib.inputs, "A_Float"))
     nt.links.new(across.outputs["Fac"], _sock(fib.inputs, "B_Float"))
+    sharp = nt.nodes.new("ShaderNodeMapRange")
+    sharp.inputs["From Min"].default_value = 0.38
+    sharp.inputs["From Max"].default_value = 0.62
+    nt.links.new(_sock(fib.outputs, "Result_Float"), sharp.inputs["Value"])
+    # Flake seams: a saw wave along X at the flake pitch, its drop warped by
+    # noise so the seams wander like packed slices instead of ruled lines.
+    wave = nt.nodes.new("ShaderNodeTexWave")
+    wave.wave_type = "BANDS"
+    wave.bands_direction = "X"
+    wave.wave_profile = "SAW"
+    wave.inputs["Scale"].default_value = 1.0 / FLAKE_W / 2.6
+    wave.inputs["Distortion"].default_value = 2.4
+    wave.inputs["Detail"].default_value = 2.0
+    wave.inputs["Detail Scale"].default_value = 1.5
+    nt.links.new(coord.outputs["Object"], wave.inputs["Vector"])
+    seam = nt.nodes.new("ShaderNodeMapRange")
+    seam.interpolation_type = "SMOOTHSTEP"
+    seam.inputs["From Min"].default_value = 0.0
+    seam.inputs["From Max"].default_value = 0.09
+    seam.inputs["To Min"].default_value = 1.0
+    seam.inputs["To Max"].default_value = 0.0
+    nt.links.new(wave.outputs["Fac"], seam.inputs["Value"])
     ramp = nt.nodes.new("ShaderNodeValToRGB")
-    ramp.color_ramp.elements[0].position = 0.34
-    ramp.color_ramp.elements[0].color = (0.36, 0.25, 0.075, 1.0)
-    ramp.color_ramp.elements[1].position = 0.66
-    ramp.color_ramp.elements[1].color = (0.88, 0.71, 0.31, 1.0)
-    nt.links.new(_sock(fib.outputs, "Result_Float"), ramp.inputs["Fac"])
+    ramp.color_ramp.elements[0].position = 0.0
+    ramp.color_ramp.elements[0].color = (0.30, 0.21, 0.065, 1.0)
+    mid = ramp.color_ramp.elements.new(0.55)
+    mid.color = (0.66, 0.50, 0.19, 1.0)
+    ramp.color_ramp.elements[-1].position = 1.0
+    ramp.color_ramp.elements[-1].color = (0.93, 0.79, 0.42, 1.0)
+    nt.links.new(sharp.outputs["Result"], ramp.inputs["Fac"])
+    shade = nt.nodes.new("ShaderNodeMix")
+    shade.data_type = "RGBA"
+    shade.blend_type = "MULTIPLY"
+    nt.links.new(seam.outputs["Result"], _sock(shade.inputs, "Factor_Float"))
+    nt.links.new(ramp.outputs["Color"], _sock(shade.inputs, "A_Color"))
+    _sock(shade.inputs, "B_Color").default_value = (0.38, 0.33, 0.25, 1.0)
     patch = nt.nodes.new("ShaderNodeTexNoise")
     patch.inputs["Scale"].default_value = 4.0
     patch.inputs["Detail"].default_value = 2.0
@@ -897,18 +934,25 @@ def straw_material(name):
     green.data_type = "RGBA"
     green.blend_type = "MULTIPLY"
     nt.links.new(patch.outputs["Fac"], _sock(green.inputs, "Factor_Float"))
-    nt.links.new(ramp.outputs["Color"], _sock(green.inputs, "A_Color"))
+    nt.links.new(_sock(shade.outputs, "Result_Color"), _sock(green.inputs, "A_Color"))
     _sock(green.inputs, "B_Color").default_value = (0.90, 0.95, 0.74, 1.0)
     nt.links.new(_sock(green.outputs, "Result_Color"), bsdf.inputs["Base Color"])
+    # Dry stems carry a waxy sheen; the gaps between them are matte.
     rough = nt.nodes.new("ShaderNodeMapRange")
-    rough.inputs["To Min"].default_value = 0.95
-    rough.inputs["To Max"].default_value = 0.70
-    nt.links.new(_sock(fib.outputs, "Result_Float"), rough.inputs["Value"])
+    rough.inputs["To Min"].default_value = 0.92
+    rough.inputs["To Max"].default_value = 0.58
+    nt.links.new(sharp.outputs["Result"], rough.inputs["Value"])
     nt.links.new(rough.outputs["Result"], bsdf.inputs["Roughness"])
+    # Stem relief minus the seam groove, one height field for the bump.
+    height = nt.nodes.new("ShaderNodeMath")
+    height.operation = "MULTIPLY_ADD"
+    nt.links.new(seam.outputs["Result"], height.inputs[0])
+    height.inputs[1].default_value = -1.2
+    nt.links.new(sharp.outputs["Result"], height.inputs[2])
     bump = nt.nodes.new("ShaderNodeBump")
-    bump.inputs["Strength"].default_value = 0.65
+    bump.inputs["Strength"].default_value = 0.8
     bump.inputs["Distance"].default_value = 0.004
-    nt.links.new(_sock(fib.outputs, "Result_Float"), bump.inputs["Height"])
+    nt.links.new(height.outputs["Value"], bump.inputs["Height"])
     nt.links.new(bump.outputs["Normal"], bsdf.inputs["Normal"])
     return mat
 
@@ -1440,12 +1484,19 @@ def half_y_at(x0, half_window):
     return 0, low, high, hay, tex, collider
 
 
+# The bake lands in per-face UV cells (the zero-AABB-overlap budget), so its
+# tangent frame breaks at every cell. At full strength those breaks cut dark
+# gashes along the top edge; the procedural stems carry the fine detail, and
+# the bake keeps the flake relief at this weight.
+NRM_STRENGTH = 0.55
+
+
 def wire_normal(mat, tex):
     """Baked normal map into the BSDF, under the fibre bump if there is one."""
     nt = mat.node_tree
     bsdf = nt.nodes["Principled BSDF"]
     nrm = nt.nodes.new("ShaderNodeNormalMap")
-    nrm.inputs["Strength"].default_value = 1.0
+    nrm.inputs["Strength"].default_value = NRM_STRENGTH
     nt.links.new(tex.outputs["Color"], nrm.inputs["Color"])
     bump = next((n for n in nt.nodes if n.bl_idname == "ShaderNodeBump"), None)
     if bump is not None: