fix(vehicle): the glazing reads as glass

The windows material was metallic 1.0 with roughness 0.0, which renders as a black void -
indistinguishable from a cabin with no glass at all. It is now tinted translucent: opacity
0.85, roughness 0.08, dark blue-grey base. The windscreen and side glass read as glass.

Opacity 0.45 was tried first and was worse than either extreme: the glass became invisible
and the greenhouse looked open again. The number is recorded in the tool's log line so the
next person does not repeat it.

The vision judge still returns verdict=no for this frame, disputing that the glazing is dark
and the wheels visible. The image shows both. It is an advisory helper - AGENTS.md says it
never replaces the human verdict - so the disagreement is written into
Screenshots/README.md rather than being resolved by iterating against the model.

TODO.md

@@ -25,7 +25,7 @@ Actionable task list for this project. This file is the single, central place fo
   - **Still open:** above ground, the capture still shows road plus a shadow and no car. Panels report `visible=1`, `mesh=SM_Vehicle_Body`, extent 238 cm, at the expected position; `MarkRenderStateDirty()` and `UpdateBounds()` run after registration. Next suspects: the pawn's own `SetActorHiddenInGame` path (a vehicle pawn is not a plain actor), or the panels being attached to a root that the physics simulation moves independently of the actor transform.
 - [x] Fix the character and car floating. Character: the player start at Z 600 left the soles 39 cm in the air (the capsule settles at 561 on this pavement); the start is now the measured 561. Car: the template's lowest geometry is exhaust, so grounding on the whole model put the tyres 4 cm above the origin - it is now grounded on its wheels, staged at Z 342 after the traced road height (366) disagreed with the visible road by ~25 cm.
 - [x] Fix the vehicle's material colour. The template's `car paint` is a legacy mix-shader graph that the FBX exporter cannot map, so `SM_Vehicle_Body` imported holding `WorldGridMaterial` and rendered black while Blender showed red. Legacy graphs are now converted to Principled before export (saturated colour wins over the grey diffuse next to it), and the staged body panel is assigned `M_Vehicle_HatchPaint`. Judge: `verdict=yes confidence=0.9`.
-- [ ] Fix the missing vehicle glazing. The greenhouse reads as open from the review angle: the glass system is mispositioned or drawn behind the body.
+- [x] Fix the missing vehicle glazing. The `windows` material was metallic 1.0 with roughness 0.0 - a black void that read as an empty cabin. Now tinted translucent (opacity 0.85, roughness 0.08); opacity 0.45 was tried first and made the glass invisible. The vision judge still returns `verdict=no` for the frame, disagreeing with what is visibly tinted glass; it is advisory, and the human verdict decides.
 - [ ] Implement enter/exit interaction.
 - [ ] Build a closed driving route with boundaries.
 - [ ] Tune basic handling to a drivable state.

Tools/ue_vehicle_materials.py

@@ -47,6 +47,34 @@ def existing_material_name(name):
     return None
 
 
+def make_translucent_glass(material):
+    """Turn a material into dark, slightly transparent glass.
+
+    The template's `windows` material is metallic 1.0 with roughness 0.0, which reads as a
+    black void in game - indistinguishable from an empty cabin. Glass needs translucency and
+    a little roughness to catch a highlight.
+    """
+    lib = unreal.MaterialEditingLibrary
+    material.set_editor_property("blend_mode", unreal.BlendMode.BLEND_TRANSLUCENT)
+    material.set_editor_property("two_sided", False)
+    for node in list(lib.get_material_expressions(material)):
+        lib.delete_material_expression(material, node)
+    base = lib.create_material_expression(material, unreal.MaterialExpressionConstant3Vector, -400, 0)
+    base.set_editor_property("constant", unreal.LinearColor(0.02, 0.03, 0.045, 1.0))
+    lib.connect_material_property(base, "", unreal.MaterialProperty.MP_BASE_COLOR)
+    opacity = lib.create_material_expression(material, unreal.MaterialExpressionConstant, -400, 140)
+    opacity.set_editor_property("r", 0.85)
+    lib.connect_material_property(opacity, "", unreal.MaterialProperty.MP_OPACITY)
+    rough = lib.create_material_expression(material, unreal.MaterialExpressionConstant, -400, 220)
+    rough.set_editor_property("r", 0.08)
+    lib.connect_material_property(rough, "", unreal.MaterialProperty.MP_ROUGHNESS)
+    specular = lib.create_material_expression(material, unreal.MaterialExpressionConstant, -400, 300)
+    specular.set_editor_property("r", 1.0)
+    lib.connect_material_property(specular, "", unreal.MaterialProperty.MP_SPECULAR)
+    lib.recompile_material(material)
+    return material
+
+
 def replace_material(name, spec, create_if_missing=False):
     resolved = existing_material_name(name)
     if resolved is not None:
@@ -87,8 +115,12 @@ def main():
     log(f"{len(materials)} materials in the Blender report")
     made = 0
     for name, spec in materials.items():
-        if replace_material(name, spec):
+        material = replace_material(name, spec)
+        if material:
             made += 1
+        if material and name.lower() == "windows":
+            make_translucent_glass(material)
+            log("windows: tinted glass (opacity 0.85, roughness 0.08) - 0.45 read as no glass at all")
     # The body arrives without a usable material (its FBX slot resolves to
     # WorldGridMaterial), so its paint is created under a name of our own and assigned to
     # the staged panel at runtime.