fix(showcase): make the water-trough water read as liquid and rust its iron

The water was a flat teal panel. Larger ripples (noise scale 22 to 7)
under a stronger bump (0.08 to 0.30) at roughness 0.03 catch the key as
glints, and the render path enables EEVEE screen-space raytracing (4.2+)
so the staves mirror in the surface. The iron gets vertically stretched
rust runs that dull its metallic response. No geometry or budget change.
A lower camera to show the hull straps was tried and rejected (the water
dropped out of view); the hero camera is unchanged.

Evidence (live, local .scratch binaries):
- Blender 5.2.1 LTS and 4.5.11 LTS: default exit 0; --skip-decimate 9,
  --stray-vert 15, --lift-z 16, --short-legs 16, --box-ends 17,
  --float-strap 18, --narrow-hull 19, --open-ends 18, --slab-ends 20 on both.
- --output passes framing on both (fill y 0.794).
- Contact sheet: luma 0.181 / stage 0.179 / warmth +0.049 / sat 0.138.
- Asset sheet: not the least-designed object in the lineup.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: TMHSDigital

docs/gallery/asset-sheets/water-trough.webp

@@ -138,6 +138,8 @@ The third pass darkened the grazing tint from a pale grey-blue (0.20,
 the surface near grazing, where that tint wins, and it read as a
 painted slab.
 
+The fourth pass made the surface read as liquid rather than as a teal panel: larger ripples (noise scale 22 to 7) under a stronger bump (0.08 to 0.30) at roughness 0.03 catch the key as glints, and the render path turns on EEVEE screen-space raytracing (4.2+) so the staves mirror in the water. The iron gets vertically stretched rust runs that dull its metallic response. A lower camera was tried to show the hull straps and rejected: the water surface dropped out of view.
+
 ### Falsifiers
 
 Each violates one named budget. All nine were run on 4.5.11, 5.1.2 and

docs/gallery/assets/water-trough-hero.webp

@@ -756,7 +756,7 @@ def water_material(name):
     mat.use_nodes = True
     nt = mat.node_tree
     bsdf = nt.nodes["Principled BSDF"]
-    bsdf.inputs["Roughness"].default_value = 0.06
+    bsdf.inputs["Roughness"].default_value = 0.03
     bsdf.inputs["IOR"].default_value = 1.33
     # Deep body where the view looks straight down, a pale sky tint toward
     # grazing angles. A light placed to reflect in the surface was
@@ -774,12 +774,12 @@ def water_material(name):
     nt.links.new(_sock(tint.outputs, "Result_Color"), bsdf.inputs["Base Color"])
     coord = nt.nodes.new("ShaderNodeTexCoord")
     noise = nt.nodes.new("ShaderNodeTexNoise")
-    noise.inputs["Scale"].default_value = 22.0
-    noise.inputs["Detail"].default_value = 3.0
+    noise.inputs["Scale"].default_value = 7.0
+    noise.inputs["Detail"].default_value = 4.0
     nt.links.new(coord.outputs["Object"], noise.inputs["Vector"])
     bump = nt.nodes.new("ShaderNodeBump")
-    bump.inputs["Strength"].default_value = 0.08
-    bump.inputs["Distance"].default_value = 0.004
+    bump.inputs["Strength"].default_value = 0.30
+    bump.inputs["Distance"].default_value = 0.006
     nt.links.new(noise.outputs["Fac"], bump.inputs["Height"])
     nt.links.new(bump.outputs["Normal"], bsdf.inputs["Normal"])
     return mat
@@ -789,10 +789,41 @@ def trough_materials():
     """(wood, iron, water): shared by the check, the render and inspection."""
     wood = wood_material("TroughWood")
     metal = principled("TroughIron", (0.16, 0.155, 0.15, 1.0), 0.85, 0.42, roughness_var=0.10)
+    rust_streaks(metal)
     water = water_material("TroughWater")
     return wood, metal, water
 
 
+def rust_streaks(mat):
+    """Wet iron rusts in runs down the strap: rust tone and dull roughness
+    wherever a vertically stretched noise crosses a threshold."""
+    nt = mat.node_tree
+    bsdf = nt.nodes["Principled BSDF"]
+    coord = nt.nodes.new("ShaderNodeTexCoord")
+    stretch = nt.nodes.new("ShaderNodeMapping")
+    stretch.inputs["Scale"].default_value = (1.0, 1.0, 0.25)
+    nt.links.new(coord.outputs["Object"], stretch.inputs["Vector"])
+    noise = nt.nodes.new("ShaderNodeTexNoise")
+    noise.inputs["Scale"].default_value = 26.0
+    noise.inputs["Detail"].default_value = 5.0
+    nt.links.new(stretch.outputs["Vector"], noise.inputs["Vector"])
+    ramp = nt.nodes.new("ShaderNodeMapRange")
+    ramp.inputs["From Min"].default_value = 0.46
+    ramp.inputs["From Max"].default_value = 0.66
+    nt.links.new(noise.outputs["Fac"], ramp.inputs["Value"])
+    mix = nt.nodes.new("ShaderNodeMix")
+    mix.data_type = "RGBA"
+    nt.links.new(ramp.outputs["Result"], _sock(mix.inputs, "Factor_Float"))
+    _sock(mix.inputs, "A_Color").default_value = bsdf.inputs["Base Color"].default_value
+    _sock(mix.inputs, "B_Color").default_value = (0.20, 0.075, 0.028, 1.0)
+    nt.links.new(_sock(mix.outputs, "Result_Color"), bsdf.inputs["Base Color"])
+    metal = nt.nodes.new("ShaderNodeMapRange")
+    metal.inputs["To Min"].default_value = 0.85
+    metal.inputs["To Max"].default_value = 0.15
+    nt.links.new(ramp.outputs["Result"], metal.inputs["Value"])
+    nt.links.new(metal.outputs["Result"], bsdf.inputs["Metallic"])
+
+
 def assign_slots(obj, wood, metal, water):
     mats = obj.data.materials
     wanted = (wood, metal, water)
@@ -1549,6 +1580,10 @@ def light(name, loc, energy, size, col, rot):
             scene.eevee.taa_render_samples = 64
         except AttributeError:
             pass
+        # screen-space raytracing lets the water mirror the staves above it,
+        # which is what makes a dark surface read as liquid (EEVEE Next, 4.2+)
+        if hasattr(scene.eevee, "use_raytracing"):
+            scene.eevee.use_raytracing = True
     scene.render.resolution_x = 1280
     scene.render.resolution_y = 720
     scene.render.image_settings.file_format = (