feat(render) Campaign FW3.1: production walk world data behind the seam

The retail frame walk's world model now materializes from production
landblock-build owners through the legal IDatReaderWriter seam, with
zero frame wiring (FW3.2 roots the frame):

- WalkCellFactory: WalkCell built in the SAME pass as LoadedCell
  (EnvCellLandblockBuild.BuildVisibilityCell) from the raw portal
  Flags/polygons/planes/stab lists already parsed there; stored as
  LoadedCell.Walk, committed atomically with the cell. The
  fixture-pinned decodes (inverse-0x2 portal side, 0xFFFF->0xFFFFFFFF
  exit widening) live here.
- WalkBuildingFactory + WalkBuildingRegistry: the production
  WalkBuilding build (drawing BSP with PORT nodes, degrade ladder,
  portal sides/stab lists, sort center, model frame) from the SAME
  LandBlockInfo the streaming build already fetches, under the
  factory's existing DAT lock - closing the gap where BuildingLoader
  drops every walk field at load.
- WalkLandscapeAssembler: the retail 51x51 viewer-centred grid
  (mid_radius 25) fed incrementally from landblock publish/retire;
  per-block z-slab (heightTable[max]+200 / [min]-1) computed
  worker-side in LandblockBuildFactory from the heights already in
  hand. O(1) SetViewer on same-block frames.
- WalkProductionFrameContext: the walk's frame contexts over
  CellVisibility + WalkBuildingRegistry with a generic
  inverse-view-projection ray caster (rays feed cross products only -
  scale-free) and the znear=0.1 CY plane.
- Publication: LandblockRenderPublisher owns both walk registries,
  publishing in the same AdvanceCompleteOne step as BuildingRegistry
  and retiring in RemoveBuildingRegistry - same commit, same
  retirement, no new ticket stage.

Conformance: ALL TEN oracle fixtures replay identically through the
PRODUCTION builders (WalkProductionWorldConformanceTests) - same
signatures as the test adapter, first run. Known gap documented for
FW3.2: far-tier landblocks carry no EnvCell transaction, so their
z-slab never reaches the assembler.

Suites: full Release build 0 warnings; Walk lane 186/1 skip;
hermetic 6,738/0 (+24); RuntimeDatAccessArchitectureTests green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/AcDream.App.Tests/Streaming/LandblockBuildFactoryTests.cs

@@ -89,6 +89,74 @@ public sealed class LandblockBuildFactoryTests
         Assert.Empty(result.Collisions.EnvCells);
     }
 
+    [Fact]
+    public void BuildNear_PopulatesWalkZSlabUnconditionallyAndWalkBuildingsFromLandBlockInfo()
+    {
+        // Campaign FW3.1: EnvCellLandblockBuild.WalkMaxZ/WalkMinZ/WalkBuildings
+        // must be populated by the production streaming build — hermetic
+        // (no installed DAT needed), mirroring the RecordingDatProxy fixture
+        // pattern the rest of this file already uses.
+        var dat = CreateDat(out RecordingDatProxy proxy);
+        AddNearFixture(proxy, LandblockId, environmentId: 1);
+        var heights = new byte[81];
+        Array.Fill(heights, (byte)10);
+        heights[0] = 200;   // one outlier byte -> a distinct maxByte from the rest.
+        proxy.Add(LandblockId, new LandBlock { Id = LandblockId, Height = heights });
+        proxy.Add(
+            (LandblockId & 0xFFFF0000u) | 0xFFFEu,
+            new LandBlockInfo
+            {
+                NumCells = 1,
+                Buildings = new List<BuildingInfo>
+                {
+                    new BuildingInfo
+                    {
+                        ModelId = 0x01234567u,
+                        Frame = new Frame
+                        {
+                            Origin = new Vector3(12f, 12f, 0f),
+                            Orientation = Quaternion.Identity,
+                        },
+                        Portals = new List<BuildingPortal>(),
+                    },
+                },
+            });
+        var heightTable = new float[256];
+        heightTable[10] = 5f;
+        heightTable[200] = 40f;
+        var factory = new LandblockBuildFactory(
+            dat, TestPreparedCollisionSource.Instance, new object(), heightTable);
+
+        LandblockBuild? result = factory.Build(Request(LandblockStreamJobKind.LoadNear));
+
+        Assert.NotNull(result);
+        var envCells = Assert.IsType<AcDream.App.Rendering.Wb.EnvCellLandblockBuild>(
+            result.EnvCells);
+        Assert.Equal(240f, envCells.WalkMaxZ);   // heightTable[200] + 200
+        Assert.Equal(4f, envCells.WalkMinZ);     // heightTable[10] - 1
+        AcDream.App.Rendering.Walk.WalkBuildingFactory.Entry buildingEntry =
+            Assert.Single(envCells.WalkBuildings);
+        // origin (12,12) -> cellX=cellY=0 -> low word 0*8+0+1 = 1.
+        Assert.Equal((LandblockId & 0xFFFF0000u) | 1u, buildingEntry.Building.PositionCellId);
+    }
+
+    [Fact]
+    public void BuildFar_NeverPopulatesWalkDataBecauseEnvCellsIsNull()
+    {
+        // Documents the known FW3.1 scope gap: far-tier (LoadFar) landblocks
+        // carry no EnvCellLandblockBuild transaction at all (terrain-only),
+        // so their z-slab/buildings never reach WalkLandscapeAssembler until
+        // a follow-up wires the far-tier path too.
+        var dat = CreateDat(out RecordingDatProxy proxy);
+        proxy.Add(LandblockId, new LandBlock { Id = LandblockId });
+        var factory = Factory(dat, new object());
+
+        LandblockBuild? result = factory.Build(Request(LandblockStreamJobKind.LoadFar));
+
+        Assert.NotNull(result);
+        Assert.Null(result.EnvCells);
+    }
+
     [Fact]
     public void NearPreparedFaultRejectsWholeGenerationWhileFarNeverReadsCollision()
     {