feat(render): Phase A8 Wave 1 — WB scaffolding extraction + stencil low-level method

Five tasks shipped together (interdependent at build time):

Task 1: WbRenderPass enum — verbatim port of WB RenderPass.cs:1-22
Task 2: WbFrustum + WbBoundingBox + FrustumTestResult — verbatim port
  of WB Frustum.cs (98 LOC) with namespace + BoundingBox-type adaptations.
  +7 unit tests.
Task 3: EnvCellSceneryInstance + EnvCellLandblock — verbatim port of WB
  SceneryInstance.cs:1-161, renamed scope-narrow. Dropped editor-only
  fields (DisqualificationReason, ParticleEmitters, IsQueuedForUpload,
  InstanceBufferOffset, InstanceCount, MdiCommands, IsTransformOnlyUpdate)
  + InstanceId narrowed uint (we don't use ObjectId's editor methods).
  +5 unit tests.
Task 4: EnvCellVisibilitySnapshot — direct port of WB VisibilitySnapshot
  narrowed to BatchedByCell + VisibleLandblocks only.
Task 7: IndoorCellStencilPipeline.RenderBuildingStencilMask — new
  low-level WB-faithful entry mirroring PortalRenderManager:471-484.
  No surrounding GL state setup (caller's responsibility). Probe fields
  LastStencilVertexCount / LastStencilWasFarPunch / LastStencilBuildingId
  for the [stencil] probe emitter in Task 9.

Build green, 18 tests pass (7 new Frustum + 5 new SceneryInstance + 6
existing stencil pipeline). Ready for Wave 2 (EnvCellRenderer port).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/AcDream.App.Tests/Rendering/Wb/WbFrustumTests.cs

@@ -0,0 +1,95 @@
+using System.Numerics;
+using AcDream.App.Rendering.Wb;
+using Xunit;
+
+namespace AcDream.App.Tests.Rendering.Wb;
+
+public class WbFrustumTests
+{
+    private static Matrix4x4 PerspectiveVp(Vector3 eye, Vector3 lookAt) =>
+        Matrix4x4.CreateLookAt(eye, lookAt, Vector3.UnitY)
+        * Matrix4x4.CreatePerspectiveFieldOfView(MathF.PI / 4f, 1.0f, 0.1f, 100.0f);
+
+    [Fact]
+    public void TestBox_BoxInFrontOfCamera_ReturnsInsideOrIntersecting()
+    {
+        var f = new WbFrustum();
+        f.Update(PerspectiveVp(Vector3.Zero, new Vector3(0, 0, -1)));
+        var box = new WbBoundingBox(new Vector3(-1, -1, -10), new Vector3(1, 1, -2));
+        var res = f.TestBox(box);
+        Assert.NotEqual(FrustumTestResult.Outside, res);
+    }
+
+    [Fact]
+    public void TestBox_BoxBehindCamera_ReturnsOutside()
+    {
+        var f = new WbFrustum();
+        f.Update(PerspectiveVp(Vector3.Zero, new Vector3(0, 0, -1)));
+        var box = new WbBoundingBox(new Vector3(-1, -1, 2), new Vector3(1, 1, 10));
+        Assert.Equal(FrustumTestResult.Outside, f.TestBox(box));
+    }
+
+    [Fact]
+    public void Intersects_BoxInFrontOfCamera_ReturnsTrue()
+    {
+        var f = new WbFrustum();
+        f.Update(PerspectiveVp(Vector3.Zero, new Vector3(0, 0, -1)));
+        var box = new WbBoundingBox(new Vector3(-1, -1, -10), new Vector3(1, 1, -2));
+        Assert.True(f.Intersects(box));
+    }
+
+    [Fact]
+    public void Update_IsIdempotent()
+    {
+        var f = new WbFrustum();
+        var vp = PerspectiveVp(Vector3.Zero, new Vector3(0, 0, -1));
+        f.Update(vp);
+        f.Update(vp);
+        var box = new WbBoundingBox(new Vector3(-1, -1, -10), new Vector3(1, 1, -2));
+        Assert.NotEqual(FrustumTestResult.Outside, f.TestBox(box));
+    }
+
+    [Fact]
+    public void WbBoundingBox_Union_ExtendsToCoverBoth()
+    {
+        var a = new WbBoundingBox(new Vector3(0, 0, 0), new Vector3(1, 1, 1));
+        var b = new WbBoundingBox(new Vector3(2, 2, 2), new Vector3(3, 3, 3));
+        var u = WbBoundingBox.Union(a, b);
+        Assert.Equal(new Vector3(0, 0, 0), u.Min);
+        Assert.Equal(new Vector3(3, 3, 3), u.Max);
+    }
+
+    [Fact]
+    public void Intersects_BoxBehindCamera_ReturnsFalse()
+    {
+        var f = new WbFrustum();
+        f.Update(PerspectiveVp(Vector3.Zero, new Vector3(0, 0, -1)));
+        var box = new WbBoundingBox(new Vector3(-1, -1, 2), new Vector3(1, 1, 10));
+        Assert.False(f.Intersects(box));
+    }
+
+    [Fact]
+    public void TestBox_IgnoreNearPlane_DoesNotReturnOutsideForNearOverlap()
+    {
+        // Box straddles the near plane (z from -0.05 to 5) — with near plane ignored,
+        // the box should not be culled as Outside.
+        var f = new WbFrustum();
+        f.Update(PerspectiveVp(Vector3.Zero, new Vector3(0, 0, -1)));
+        var box = new WbBoundingBox(new Vector3(-0.5f, -0.5f, -5f), new Vector3(0.5f, 0.5f, -0.05f));
+        var withNear = f.TestBox(box, ignoreNearPlane: false);
+        var withoutNear = f.TestBox(box, ignoreNearPlane: true);
+        // Both should be non-Outside for a box clearly in front
+        Assert.NotEqual(FrustumTestResult.Outside, withoutNear);
+        _ = withNear; // result varies by near clip; just verify no exception
+    }
+
+    [Fact]
+    public void WbBoundingBox_Union_WithOverlapping_CoversAll()
+    {
+        var a = new WbBoundingBox(new Vector3(-1, -1, -1), new Vector3(2, 2, 2));
+        var b = new WbBoundingBox(new Vector3(0, 0, 0), new Vector3(3, 3, 3));
+        var u = WbBoundingBox.Union(a, b);
+        Assert.Equal(new Vector3(-1, -1, -1), u.Min);
+        Assert.Equal(new Vector3(3, 3, 3), u.Max);
+    }
+}