fix #451: stabilize portal seam rendering

docs/ISSUES.md

@@ -24,6 +24,48 @@ What does NOT go here:
 - Every session: scan OPEN issues at start; promote/close anything we touched during the session before ending.
 - Promoting to a Phase: mark as `DONE (promoted to Phase X)` + commit SHA where the Phase entry landed.
 
+## #451 — Sanctuary cathedral portal seam leaks exterior world and particles
+
+**Status:** DONE — OWNER-ACCEPTED 2026-08-27 ("Looks good! Gate pass now!").
+**Component:** Vulkan PView / nested building look-ins / landscape alpha ordering.
+
+At the open-air Sanctuary cathedral seam between `0xF4180104` and
+`0xF4180106`, small player or chase-camera movements could make cathedral
+halves, their shadows, or floor textures flap; expose the world background,
+trees, a nearby building, and waterfall/steam particles through opaque
+geometry; or clip the local player in half. Camera zoom alone reproduced the
+failure. The final particle repro was
+`0xF4180104 [31.111177 57.648911 169.804993]`.
+
+This was a renderer contract failure, not bad Sanctuary data. The correction:
+
+- classifies exterior building seeds with retail's `F_EPSILON` instead of the
+  ordinary 1 cm EnvCell traversal tolerance and retains the exact accepted
+  `CBldPortal` aperture;
+- appends every nested look-in cell's own `portal_view` to the frame clip
+  buffer, punches only the accepted seed portal, and clips shells plus static
+  and particle alpha to that view;
+- pairs each look-in with only its own exterior building shell and reproduces
+  retail's per-building alpha barriers;
+- keeps dynamic objects whole after the CPU PortalList sphere test, matching
+  retail `DrawMesh` and preventing the player-slicing regression;
+- submits attached and ownerless exterior particles inside `LScape::draw` for
+  every PView root, eliminating the late post-world replay that let waterfall
+  alpha repaint already-drawn cathedral cells; and
+- treats authored `SeenOutside` open-air cells as atmospheric outdoor cells so
+  sky/shadow activation no longer flips merely because the camera acquired an
+  EnvCell root.
+
+The fix is renderer-wide: no Sanctuary coordinate or asset special case is
+present in production. Installed-DAT regressions retain the reported camera
+handoff, lateral transition, and exact steam-seam views. The temporary live
+emitter/shell trace was removed at closeout.
+
+**Acceptance:** owner swept both cells, moved across the seam, and zoomed the
+camera through the former trigger positions. Cathedral/world flapping, shadow
+toggle, player clipping, exterior geometry, and waterfall/particle bleed were
+absent in the accepted build.
+
 ## #450 — Fast character re-entry after logout can remain in portal space at `lb 0/0`
 
 **Status:** DONE — OWNER-ACCEPTED 2026-08-26 in the combined client-parity gate.
@@ -18959,6 +19001,13 @@ DrawDynamicsParticles only sees dynamics-last cone survivors.
 **Gate:** stand inside, look out the doorway at the town portal — the
 swirl renders through the door.
 
+**2026-08-27 ordering correction (#451):** the old "once per frame after the
+look-ins" placement was sufficient for this gate but did not preserve the
+installed `outside_view` and could repaint an already-drawn open-air building.
+Ownerless emitters now submit once per outside-view slice with that slice's
+clip slot. When building look-ins exist they enter the pre-building alpha
+barrier; otherwise they drain at the end of `LScape::draw`.
+
 ---
 
 ## #132 — Candle flame disappears when the through-opening background is behind it
@@ -18999,6 +19048,13 @@ against interiors). The owner-id filter carries over; cell-pass and
 dynamics-pass emitters keep their own passes (owners never in the
 outdoor-static set → no double-draw).
 
+**2026-08-27 correction (#451):** the post-frame placement fixed this narrow
+flame-overpaint case but was too late for nested open-air cathedral cells: an
+exterior waterfall could repaint their completed opaque floor. Outdoor-static
+and ownerless particles now submit inside `LScape::draw` under the exact
+outside-view clip slot, with retail's pre-building/per-building alpha barriers;
+the post-world PView replay is deleted.
+
 **Gate:** both sides — indoors with the opening behind the candle, and
 outdoors at the angle that previously erased it.
 

src/AcDream.App/Rendering/ClipFrameAssembler.cs

@@ -39,6 +39,13 @@ public enum TerrainClipMode
 /// </summary>
 public readonly record struct ClipViewSlice(int Slot, Vector4 NdcAabb, Vector4[] Planes);
 
+/// <summary>
+/// Identifies one cell inside one nested building look-in. The same EnvCell can
+/// be reached by more than one building PView, so a cell id alone is not a
+/// sufficient routing key.
+/// </summary>
+public readonly record struct LookInClipCell(int FrameIndex, uint CellId);
+
 /// <summary>
 /// Result of <see cref="ClipFrameAssembler.Assemble"/>: populated clip buffers
 /// plus routing data consumed by the render orchestration.
@@ -57,6 +64,12 @@ public sealed class ClipFrameAssembly
     /// <summary>Full retail portal_view slices per visible cell.</summary>
     public Dictionary<uint, ClipViewSlice[]> CellIdToViewSlices { get; } = new();
 
+    /// <summary>First drawable slice slot per nested look-in cell.</summary>
+    public Dictionary<LookInClipCell, int> LookInCellToSlot { get; } = new();
+
+    /// <summary>All retail portal_view slices per nested look-in cell.</summary>
+    public Dictionary<LookInClipCell, ClipViewSlice[]> LookInCellToViewSlices { get; } = new();
+
     /// <summary>Full retail outside_view slices.</summary>
     public ClipViewSlice[] OutsideViewSlices { get; private set; } = System.Array.Empty<ClipViewSlice>();
 
@@ -93,6 +106,8 @@ public sealed class ClipFrameAssembly
         Frame = frame;
         foreach (ClipViewSlice[] slices in CellIdToViewSlices.Values)
             ReturnSlices(slices);
+        foreach (ClipViewSlice[] slices in LookInCellToViewSlices.Values)
+            ReturnSlices(slices);
         foreach (int[] slots in CellIdToViewSlots.Values)
             ReturnSlots(slots);
         if (OutsideViewSlices.Length != 0)
@@ -101,6 +116,8 @@ public sealed class ClipFrameAssembly
         CellIdToSlot.Clear();
         CellIdToViewSlots.Clear();
         CellIdToViewSlices.Clear();
+        LookInCellToSlot.Clear();
+        LookInCellToViewSlices.Clear();
         PerCellPlaneCounts.Clear();
         OutsideViewSlices = System.Array.Empty<ClipViewSlice>();
         SliceScratch.Clear();
@@ -363,6 +380,70 @@ public static class ClipFrameAssembler
         return assembly;
     }
 
+    /// <summary>
+    /// Appends the cell views used by nested <c>DrawBuilding -&gt; DrawPortal</c>
+    /// PViews to the already assembled frame. Retail installs each nested
+    /// cell's own <c>portal_view</c> before drawing its shell and object list;
+    /// these slots must therefore be published with the main frame before the
+    /// first draw is recorded.
+    /// </summary>
+    public static void AppendLookInFrames(
+        ClipFrame frame,
+        IReadOnlyList<PortalVisibilityFrame> lookInFrames,
+        ClipFrameAssembly assembly)
+    {
+        System.ArgumentNullException.ThrowIfNull(frame);
+        System.ArgumentNullException.ThrowIfNull(lookInFrames);
+        System.ArgumentNullException.ThrowIfNull(assembly);
+        if (!ReferenceEquals(frame, assembly.Frame))
+            throw new System.ArgumentException(
+                "The look-in slots must be appended to the assembly's clip frame.",
+                nameof(frame));
+
+        for (int frameIndex = 0; frameIndex < lookInFrames.Count; frameIndex++)
+        {
+            PortalVisibilityFrame lookIn = lookInFrames[frameIndex];
+            foreach (uint cellId in lookIn.OrderedVisibleCells)
+            {
+                if (!lookIn.CellViews.TryGetValue(cellId, out CellView? view))
+                    continue;
+
+                List<ClipViewSlice> slices = assembly.SliceScratch;
+                slices.Clear();
+                foreach (ViewPolygon poly in view.Polygons)
+                {
+                    ClipPlaneSet cps = ClipPlaneSet.From(poly);
+                    if (cps.IsNothingVisible)
+                        continue;
+
+                    int slot;
+                    Vector4[] planes;
+                    if (cps.Count > 0)
+                    {
+                        planes = cps.PlaneArray;
+                        slot = frame.AppendSlot(planes);
+                    }
+                    else
+                    {
+                        planes = System.Array.Empty<Vector4>();
+                        slot = 0;
+                        assembly.ScissorFallbacks++;
+                    }
+
+                    slices.Add(new ClipViewSlice(slot, AabbOf(poly), planes));
+                }
+
+                if (slices.Count == 0)
+                    continue;
+
+                ClipViewSlice[] packed = assembly.CopySlices(slices);
+                var key = new LookInClipCell(frameIndex, cellId);
+                assembly.LookInCellToViewSlices.Add(key, packed);
+                assembly.LookInCellToSlot.Add(key, packed[0].Slot);
+            }
+        }
+    }
+
     private static Vector4 AabbOf(ViewPolygon poly) =>
         new(poly.MinX, poly.MinY, poly.MaxX, poly.MaxY);
 

src/AcDream.App/Rendering/Packs/AtmosphericFrameInputs.cs

@@ -99,7 +99,7 @@ internal sealed class AtmosphericFrameInputState : IAtmosphericWorldFrameSink
             _host.DeltaSeconds,
             _host.ViewportWidth,
             _host.ViewportHeight,
-            IsOutdoor: world.Roots.RenderSky && !world.Roots.CameraInsideCell);
+            IsOutdoor: world.Roots.IsAtmosphericallyOutdoor);
         _published = true;
     }
 

src/AcDream.App/Rendering/Packs/AtmosphericPostProcessGraph.cs

@@ -431,8 +431,7 @@ internal sealed class AtmosphericPostProcessGraph :
         var environment = new DirectionalShadowEnvironmentInput(
             PackEnabled: true,
             PortalOrLoginCoverVisible: foundation.PortalViewportVisible,
-            PlayerInsideCell: world.Roots.PlayerInsideCell
-                || world.Roots.CameraInsideCell,
+            PlayerInsideCell: world.Roots.PlayerOrCameraInsideEnclosedCell,
             source,
             foundation.Atmosphere,
             ActiveDayGroupMultiplier: Math.Clamp(
@@ -449,7 +448,7 @@ internal sealed class AtmosphericPostProcessGraph :
         // or deactivation can never leave a stale exclusion set applied to
         // the dispatcher (see FoliageWindExclusions's doc comment).
         worldMeshes.FoliageWindExclusions = _foliageWindExclusions;
-        bool isOutdoor = world.Roots.RenderSky && !world.Roots.CameraInsideCell;
+        bool isOutdoor = world.Roots.IsAtmosphericallyOutdoor;
         AtmosphericFrameBufferBinding shadowAtmosphericFrame =
             BuildShadowAtmosphericFrameBinding(frame, foundation.Atmosphere.Kind, isOutdoor);
         var input = new DirectionalSunShadowRenderInput(

src/AcDream.App/Rendering/Packs/DeclaredFullscreenRenderPackGraph.cs

@@ -210,8 +210,7 @@ internal class DeclaredFullscreenRenderPackGraph :
         var environment = new DirectionalShadowEnvironmentInput(
             PackEnabled: true,
             PortalOrLoginCoverVisible: foundation.PortalViewportVisible,
-            PlayerInsideCell: world.Roots.PlayerInsideCell
-                || world.Roots.CameraInsideCell,
+            PlayerInsideCell: world.Roots.PlayerOrCameraInsideEnclosedCell,
             source,
             foundation.Atmosphere,
             ActiveDayGroupMultiplier: Math.Clamp(

src/AcDream.App/Rendering/ParticleRenderer.Rhi.cs

@@ -71,10 +71,8 @@ public sealed unsafe partial class ParticleRenderer
 
     private const uint QuadStrideBytes = 4 * sizeof(float);
 
-    /// <summary>Floats per mesh-particle instance: a <c>mat4</c> plus an RGBA colour.</summary>
-    internal const int MeshInstanceFloats = 20;
-
-    private const uint MeshInstanceStrideBytes = MeshInstanceFloats * sizeof(float);
+    private static readonly uint MeshInstanceStrideBytes =
+        (uint)sizeof(MeshParticleGpuInstance);
 
     /// <summary>
     /// The billboard layout: the shared unit quad at vertex rate, and one
@@ -103,7 +101,8 @@ public sealed unsafe partial class ParticleRenderer
             // Location 6 is `in uint aTextureIndex` — an INTEGER shader input,
             // so R8G8B8A8's normalized cousin would be wrong in kind. It is one
             // 32-bit unsigned value; Float1 would reinterpret its bits.
-            new GpuVertexAttribute(6, GpuVertexFormat.UInt1, 64, Binding: 1)));
+            new GpuVertexAttribute(6, GpuVertexFormat.UInt1, 64, Binding: 1),
+            new GpuVertexAttribute(7, GpuVertexFormat.UInt1, 68, Binding: 1)));
 
     /// <summary>
     /// The mesh-particle layout: the shared world-mesh vertex at vertex rate,
@@ -126,7 +125,8 @@ public sealed unsafe partial class ParticleRenderer
             new GpuVertexAttribute(4, GpuVertexFormat.Float4, 16, Binding: 1),
             new GpuVertexAttribute(5, GpuVertexFormat.Float4, 32, Binding: 1),
             new GpuVertexAttribute(6, GpuVertexFormat.Float4, 48, Binding: 1),
-            new GpuVertexAttribute(7, GpuVertexFormat.Float4, 64, Binding: 1)));
+            new GpuVertexAttribute(7, GpuVertexFormat.Float4, 64, Binding: 1),
+            new GpuVertexAttribute(8, GpuVertexFormat.UInt1, 80, Binding: 1)));
 
     /// <summary>
     /// The RHI arm's constructor. No GL context, no <c>Shader</c>, no
@@ -340,22 +340,22 @@ public sealed unsafe partial class ParticleRenderer
             while (submission.Kind == ParticleSubmissionKind.Mesh
                 && _meshDrawListScratch[submission.DrawIndex].Key == meshKey);
 
-            int neededFloats = _meshRunScratch.Count * MeshInstanceFloats;
-            if (_meshInstanceScratch.Length < neededFloats)
-                _meshInstanceScratch = new float[neededFloats + 256 * MeshInstanceFloats];
+            int neededInstances = _meshRunScratch.Count;
+            if (_meshInstanceScratch.Length < neededInstances)
+                _meshInstanceScratch = new MeshParticleGpuInstance[neededInstances + 256];
             for (int instance = 0; instance < _meshRunScratch.Count; instance++)
             {
                 WriteMeshGpuInstance(
-                    _meshInstanceScratch,
-                    instance * MeshInstanceFloats,
+                    ref _meshInstanceScratch[instance],
                     _meshRunScratch[instance]);
             }
 
-            GpuRingAllocation instances = WriteVertexRing<float>(
+            GpuRingAllocation instances = WriteVertexRing<MeshParticleGpuInstance>(
                 frame,
-                _meshInstanceScratch.AsSpan(0, neededFloats));
+                _meshInstanceScratch.AsSpan(0, neededInstances));
             DrawMeshBatchRhi(
                 encoder,
+                frame,
                 global,
                 batch,
                 viewProjection,
@@ -384,7 +384,13 @@ public sealed unsafe partial class ParticleRenderer
         GpuRingAllocation ring = WriteVertexRing<BillboardGpuInstance>(
             frame,
             _instanceScratch.AsSpan(0, instances.Count));
-        BindBillboardPipeline(encoder, viewProjection, additive, ring.Buffer, ring.OffsetBytes);
+        BindBillboardPipeline(
+            encoder,
+            frame,
+            viewProjection,
+            additive,
+            ring.Buffer,
+            ring.OffsetBytes);
         encoder.DrawIndexed(
             (uint)QuadIndices.Length,
             (uint)instances.Count,
@@ -401,6 +407,7 @@ public sealed unsafe partial class ParticleRenderer
     /// </summary>
     private void BindBillboardPipeline(
         IGpuPassEncoder encoder,
+        IGpuFrame frame,
         Matrix4x4 viewProjection,
         bool additive,
         IGpuBuffer instanceBuffer,
@@ -426,10 +433,15 @@ public sealed unsafe partial class ParticleRenderer
         encoder.BindVertexBuffer(0, _quadVertexBuffer!, 0);
         encoder.BindVertexBuffer(1, instanceBuffer, instanceOffsetBytes);
         encoder.BindIndexBuffer(_quadIndexBuffer!, 0, GpuIndexType.UInt32);
+        WorldFrameSectionBinding.BindClipRegions(
+            encoder,
+            _scope!.Sections,
+            frame);
     }
 
     private void DrawMeshBatchRhi(
         IGpuPassEncoder encoder,
+        IGpuFrame frame,
         GlobalMeshBuffer global,
         ObjectRenderBatch batch,
         Matrix4x4 viewProjection,
@@ -472,6 +484,10 @@ public sealed unsafe partial class ParticleRenderer
                 "The shared mesh arena has no index store."),
             0,
             GpuIndexType.UInt16);
+        WorldFrameSectionBinding.BindClipRegions(
+            encoder,
+            _scope!.Sections,
+            frame);
         encoder.DrawIndexed(
             (uint)batch.IndexCount,
             instanceCount,
@@ -520,9 +536,8 @@ public sealed unsafe partial class ParticleRenderer
             Array.Resize(ref _preparedInstanceOffsets, count + 256);
         if (_instanceScratch.Length < count)
             Array.Resize(ref _instanceScratch, count + 256);
-        int neededMeshFloats = count * MeshInstanceFloats;
-        if (_meshInstanceScratch.Length < neededMeshFloats)
-            _meshInstanceScratch = new float[neededMeshFloats + 256 * MeshInstanceFloats];
+        if (_meshInstanceScratch.Length < count)
+            _meshInstanceScratch = new MeshParticleGpuInstance[count + 256];
 
         int billboardCount = 0;
         int meshCount = 0;
@@ -541,8 +556,7 @@ public sealed unsafe partial class ParticleRenderer
             {
                 _preparedInstanceOffsets[i] = (uint)meshCount;
                 WriteMeshGpuInstance(
-                    _meshInstanceScratch,
-                    meshCount++ * MeshInstanceFloats,
+                    ref _meshInstanceScratch[meshCount++],
                     deferred.Mesh.Instance);
             }
         }
@@ -553,9 +567,9 @@ public sealed unsafe partial class ParticleRenderer
                 _instanceScratch.AsSpan(0, billboardCount)))
             : default;
         _preparedMeshInstances = meshCount > 0
-            ? SectionOf(WriteVertexRing<float>(
+            ? SectionOf(WriteVertexRing<MeshParticleGpuInstance>(
                 frame,
-                _meshInstanceScratch.AsSpan(0, meshCount * MeshInstanceFloats)))
+                _meshInstanceScratch.AsSpan(0, meshCount)))
             : default;
         _preparedAlphaCount = count;
     }
@@ -591,6 +605,7 @@ public sealed unsafe partial class ParticleRenderer
                 {
                     BindBillboardPipeline(
                         encoder,
+                        RequireRhiFrame(),
                         viewProjection,
                         key.Additive,
                         billboards,
@@ -632,6 +647,7 @@ public sealed unsafe partial class ParticleRenderer
             {
                 DrawMeshBatchRhi(
                     encoder,
+                    RequireRhiFrame(),
                     global,
                     batch,
                     meshViewProjection,

src/AcDream.App/Rendering/ParticleRenderer.cs

@@ -47,6 +47,7 @@ public sealed unsafe partial class ParticleRenderer : IDisposable
         public readonly uint ColorArgb;
         public readonly AcDream.App.Rendering.Gpu.GpuTextureSlot TextureSlot;
         public readonly float DistanceSq;
+        public readonly uint ClipSlot;
 
         public ParticleInstance(
             Vector3 position,
@@ -54,7 +55,8 @@ public sealed unsafe partial class ParticleRenderer : IDisposable
             Vector3 axisY,
             uint colorArgb,
             AcDream.App.Rendering.Gpu.GpuTextureSlot textureSlot,
-            float distanceSq)
+            float distanceSq,
+            uint clipSlot)
         {
             Position = position;
             AxisX = axisX;
@@ -62,6 +64,7 @@ public sealed unsafe partial class ParticleRenderer : IDisposable
             ColorArgb = colorArgb;
             TextureSlot = textureSlot;
             DistanceSq = distanceSq;
+            ClipSlot = clipSlot;
         }
     }
 
@@ -80,6 +83,16 @@ public sealed unsafe partial class ParticleRenderer : IDisposable
         public Vector4 AxisY;
         public Vector4 Color;
         public uint TextureIndex;
+        public uint ClipSlot;
+    }
+
+    /// <summary>Vertex-instance ABI shared with particle_mesh.vert.</summary>
+    [StructLayout(LayoutKind.Sequential)]
+    internal struct MeshParticleGpuInstance
+    {
+        public Matrix4x4 Model;
+        public Vector4 Color;
+        public uint ClipSlot;
     }
 
     private readonly struct MeshParticleInstance
@@ -87,12 +100,18 @@ public sealed unsafe partial class ParticleRenderer : IDisposable
         public readonly Matrix4x4 Model;
         public readonly uint ColorArgb;
         public readonly float DistanceSq;
+        public readonly uint ClipSlot;
 
-        public MeshParticleInstance(Matrix4x4 model, uint colorArgb, float distanceSq)
+        public MeshParticleInstance(
+            Matrix4x4 model,
+            uint colorArgb,
+            float distanceSq,
+            uint clipSlot)
         {
             Model = model;
             ColorArgb = colorArgb;
             DistanceSq = distanceSq;
+            ClipSlot = clipSlot;
         }
     }
 
@@ -124,7 +143,7 @@ public sealed unsafe partial class ParticleRenderer : IDisposable
     internal (int SetCount, long CapacityBytes) DynamicBufferDiagnostics => (0, 0);
 
     private BillboardGpuInstance[] _instanceScratch = new BillboardGpuInstance[256];
-    private float[] _meshInstanceScratch = new float[256 * 20];
+    private MeshParticleGpuInstance[] _meshInstanceScratch = new MeshParticleGpuInstance[256];
 
     // MP-Alloc (2026-07-05): Draw() is called up to ~11 times per frame
     // (sky pre/post, scene, per-visible-cell, dynamics, unattached passes),
@@ -203,7 +222,8 @@ public sealed unsafe partial class ParticleRenderer : IDisposable
             cameraRight,
             cameraUp,
             emitterFilter,
-            scopedEmitters: null);
+            scopedEmitters: null,
+            clipSlot: 0);
         FinishDraw(camera, renderPass);
     }
 
@@ -213,7 +233,8 @@ public sealed unsafe partial class ParticleRenderer : IDisposable
         ParticleRenderPass renderPass,
         IReadOnlySet<uint> attachedOwnerIds,
         bool includeUnattached = false,
-        IReadOnlySet<uint>? excludedAttachedOwnerIds = null)
+        IReadOnlySet<uint>? excludedAttachedOwnerIds = null,
+        uint clipSlot = 0)
     {
         if (camera is null)
             return;
@@ -233,7 +254,8 @@ public sealed unsafe partial class ParticleRenderer : IDisposable
             cameraRight,
             cameraUp,
             emitterFilter: null,
-            _scopedEmitterScratch);
+            _scopedEmitterScratch,
+            clipSlot);
         FinishDraw(camera, renderPass);
     }
 
@@ -332,7 +354,8 @@ public sealed unsafe partial class ParticleRenderer : IDisposable
         Vector3 cameraRight,
         Vector3 cameraUp,
         Func<AcDream.Core.Vfx.ParticleEmitter, bool>? emitterFilter,
-        IReadOnlyList<RuntimeParticleEmitter>? scopedEmitters)
+        IReadOnlyList<RuntimeParticleEmitter>? scopedEmitters,
+        uint clipSlot)
     {
         var draws = _drawListScratch;
         draws.Clear();
@@ -348,6 +371,7 @@ public sealed unsafe partial class ParticleRenderer : IDisposable
                     cameraWorldPos,
                     cameraRight,
                     cameraUp,
+                    clipSlot,
                     ref sequence);
             }
             return;
@@ -356,7 +380,13 @@ public sealed unsafe partial class ParticleRenderer : IDisposable
         foreach (RuntimeParticleEmitter emitter in _particles.EnumerateRenderableEmitters(renderPass))
         {
             if (emitterFilter is null || emitterFilter(emitter))
-                AppendEmitterDraws(emitter, cameraWorldPos, cameraRight, cameraUp, ref sequence);
+                AppendEmitterDraws(
+                    emitter,
+                    cameraWorldPos,
+                    cameraRight,
+                    cameraUp,
+                    clipSlot,
+                    ref sequence);
         }
     }
 
@@ -365,6 +395,7 @@ public sealed unsafe partial class ParticleRenderer : IDisposable
         Vector3 cameraWorldPos,
         Vector3 cameraRight,
         Vector3 cameraUp,
+        uint clipSlot,
         ref int sequence)
     {
         List<ParticleDraw> draws = _drawListScratch;
@@ -385,7 +416,13 @@ public sealed unsafe partial class ParticleRenderer : IDisposable
             uint gfxObjId = em.Desc.HwGfxObjId != 0 ? em.Desc.HwGfxObjId : em.Desc.GfxObjId;
             if (gfxObjId != 0
                 && ResolveGeometryKind(gfxObjId) == RetailParticleGeometryKind.FullMesh
-                && TryAppendMeshDraws(em, p, gfxObjId, cameraWorldPos, ref sequence))
+                && TryAppendMeshDraws(
+                    em,
+                    p,
+                    gfxObjId,
+                    cameraWorldPos,
+                    clipSlot,
+                    ref sequence))
             {
                 continue;
             }
@@ -483,7 +520,8 @@ public sealed unsafe partial class ParticleRenderer : IDisposable
                     axisY,
                     p.ColorArgb,
                     gfxInfo.TextureSlot,
-                    distSq)));
+                    distSq,
+                    clipSlot)));
             _submissionScratch.Add(new ParticleSubmission(
                 ParticleSubmissionKind.Billboard,
                 drawIndex,
@@ -497,6 +535,7 @@ public sealed unsafe partial class ParticleRenderer : IDisposable
         Particle particle,
         uint gfxObjId,
         Vector3 cameraWorldPosition,
+        uint clipSlot,
         ref int sequence)
     {
         if (_meshAdapter is null || !MeshParticlesAvailable)
@@ -520,7 +559,11 @@ public sealed unsafe partial class ParticleRenderer : IDisposable
             model,
             cameraWorldPosition);
         float distanceSq = viewerDistance * viewerDistance;
-        var instance = new MeshParticleInstance(model, particle.ColorArgb, distanceSq);
+        var instance = new MeshParticleInstance(
+            model,
+            particle.ColorArgb,
+            distanceSq,
+            clipSlot);
 
         for (int batchIndex = 0; batchIndex < renderData.Batches.Count; batchIndex++)
         {
@@ -581,35 +624,24 @@ public sealed unsafe partial class ParticleRenderer : IDisposable
             TextureIndex = particle.TextureSlot.IsAssigned
                 ? particle.TextureSlot.Index
                 : NoTextureSlot,
+            ClipSlot = particle.ClipSlot,
         };
     }
 
     private static void WriteMeshGpuInstance(
-        float[] destination,
-        int offset,
+        ref MeshParticleGpuInstance destination,
         MeshParticleInstance instance)
     {
-        Matrix4x4 model = instance.Model;
-        destination[offset + 0] = model.M11;
-        destination[offset + 1] = model.M12;
-        destination[offset + 2] = model.M13;
-        destination[offset + 3] = model.M14;
-        destination[offset + 4] = model.M21;
-        destination[offset + 5] = model.M22;
-        destination[offset + 6] = model.M23;
-        destination[offset + 7] = model.M24;
-        destination[offset + 8] = model.M31;
-        destination[offset + 9] = model.M32;
-        destination[offset + 10] = model.M33;
-        destination[offset + 11] = model.M34;
-        destination[offset + 12] = model.M41;
-        destination[offset + 13] = model.M42;
-        destination[offset + 14] = model.M43;
-        destination[offset + 15] = model.M44;
-        destination[offset + 16] = ((instance.ColorArgb >> 16) & 0xFF) / 255f;
-        destination[offset + 17] = ((instance.ColorArgb >> 8) & 0xFF) / 255f;
-        destination[offset + 18] = (instance.ColorArgb & 0xFF) / 255f;
-        destination[offset + 19] = ((instance.ColorArgb >> 24) & 0xFF) / 255f;
+        destination = new MeshParticleGpuInstance
+        {
+            Model = instance.Model,
+            Color = new Vector4(
+                ((instance.ColorArgb >> 16) & 0xFF) / 255f,
+                ((instance.ColorArgb >> 8) & 0xFF) / 255f,
+                (instance.ColorArgb & 0xFF) / 255f,
+                ((instance.ColorArgb >> 24) & 0xFF) / 255f),
+            ClipSlot = instance.ClipSlot,
+        };
     }
 
     private TranslucencyKind ResolveMeshBlend(ObjectRenderBatch batch)

src/AcDream.App/Rendering/PortalVisibilityBuilder.cs

@@ -26,11 +26,21 @@ public sealed class PortalVisibilityFrame
     private int _processedViewCountsUnderusedFrames;
     private int _orderedVisibleCellsUnderusedFrames;
     private int _todoUnderusedFrames;
+    private int _exteriorSeedPortalsUnderusedFrames;
 
     internal PortalPolygonVertexStore PolygonVertices => _polygonVertices;
     internal int PolygonVertexAllocationCount => _polygonVertices.AllocationCount;
     internal int RetainedPolygonVertexArrayCount => _polygonVertices.RetainedArrayCount;
 
+    // Interior-root look-ins are constructed one building at a time. Keep
+    // the source identity on the retained frame so the landscape pass can
+    // pair retail's portal-only traversal with that building's own exterior
+    // shell instead of repainting every nearby shell after every look-in.
+    // Building ids are publication-local, so the landblock is part of the
+    // identity. An unstamped building uses its seed cell id as the key.
+    internal uint SourceBuildingKey { get; set; }
+    internal uint SourceBuildingLandblockId { get; set; }
+
     /// <summary>Screen region (NDC) where outdoor terrain/scenery may draw — exit portals
     /// recursively clipped to their portal chain. The cellar-flap fix.</summary>
     public CellView OutsideView { get; private set; } = new();
@@ -49,6 +59,15 @@ public sealed class PortalVisibilityFrame
     /// neighbour cell id that left the camera building's cell set (wire-in #3 / Step 5).</summary>
     public Dictionary<uint, CellView> CrossBuildingViews { get; } = new();
 
+    /// <summary>
+    /// Exact outside-facing building portals that successfully seeded this
+    /// exterior construction, together with the clipped view region produced
+    /// by that portal. Retail's DrawBuilding pass punches these CBldPortal
+    /// apertures themselves; it does not infer them later from every exit on a
+    /// cell reached by the resulting flood.
+    /// </summary>
+    public List<ExteriorPortalSeed> ExteriorSeedPortals { get; } = new();
+
     // Build scratch belongs to the frame so a caller that reuses a frame also reuses the large
     // hash tables and the 128-entry convergence trace. This is especially important outdoors,
     // where retail runs one small ConstructView flood per nearby building every frame.
@@ -114,6 +133,7 @@ public sealed class PortalVisibilityFrame
         int processedViewCount = ProcessedViewCountsScratch.Count;
         int orderedVisibleCellCount = OrderedVisibleCells.Count;
         int todoCount = TodoScratch.Count;
+        int exteriorSeedPortalCount = ExteriorSeedPortals.Count;
 
         if (OutsideView.IsRetainable)
             OutsideView.Reset();
@@ -121,9 +141,14 @@ public sealed class PortalVisibilityFrame
             OutsideView = new CellView();
         ReturnCellViews(CellViews);
         ReturnCellViews(CrossBuildingViews);
+        for (int index = 0; index < ExteriorSeedPortals.Count; index++)
+            ReturnCellView(ExteriorSeedPortals[index].View);
         CellViews.Clear();
         OrderedVisibleCells.Clear();
         CrossBuildingViews.Clear();
+        ExteriorSeedPortals.Clear();
+        SourceBuildingKey = 0;
+        SourceBuildingLandblockId = 0;
         QueuedScratch.Clear();
         DrawListedScratch.Clear();
         ProcessedViewCountsScratch.Clear();
@@ -152,6 +177,10 @@ public sealed class PortalVisibilityFrame
             orderedVisibleCellCount,
             ref _orderedVisibleCellsUnderusedFrames);
         TrimIfCold(TodoScratch, todoCount, ref _todoUnderusedFrames);
+        TrimIfCold(
+            ExteriorSeedPortals,
+            exteriorSeedPortalCount,
+            ref _exteriorSeedPortalsUnderusedFrames);
     }
 
     internal ViewPolygon CopyPolygon(ReadOnlySpan<Vector2> vertices)
@@ -178,11 +207,14 @@ public sealed class PortalVisibilityFrame
     private void ReturnCellViews(Dictionary<uint, CellView> views)
     {
         foreach (CellView view in views.Values)
-        {
-            view.Reset();
-            if (view.IsRetainable && _cellViewPool.Count < MaxRetainedCellViews)
-                _cellViewPool.Push(view);
-        }
+            ReturnCellView(view);
+    }
+
+    private void ReturnCellView(CellView view)
+    {
+        view.Reset();
+        if (view.IsRetainable && _cellViewPool.Count < MaxRetainedCellViews)
+            _cellViewPool.Push(view);
     }
 
     private static void TrimIfCold<TKey, TValue>(
@@ -243,6 +275,15 @@ public sealed class PortalVisibilityFrame
     }
 }
 
+/// <summary>
+/// One outside-facing portal accepted as an exterior building-view seed.
+/// <paramref name="View"/> is the exact installed-view-clipped aperture.
+/// </summary>
+public readonly record struct ExteriorPortalSeed(
+    uint CellId,
+    int PortalIndex,
+    CellView View);
+
 public static class PortalVisibilityBuilder
 {
     // Side-classification epsilon. Retail's is F_EPSILON = 0.000199999995
@@ -710,10 +751,27 @@ public static class PortalVisibilityBuilder
                 // ever built from a knife-edge aperture.
                 if (i < cell.ClipPlanes.Count)
                 {
-                    if (CameraOnInteriorSide(cell, i, cameraPos))
-                        continue;
                     if (EyeInPlaneOfPortal(cell, i, cameraPos))
                         continue;
+
+                    // Do NOT reuse the ordinary EnvCell traversal tolerance
+                    // here. PortalSideEpsilon deliberately admits a 1 cm
+                    // stale-root margin, but retail ConstructView(CBldPortal)
+                    // classifies the seed with Sidedness's exact F_EPSILON
+                    // (0.0002 m). At Sanctuary the 0104 and 0106 exterior
+                    // planes coincide; the chase eye can sit ~4 mm outside the
+                    // opposite cathedral half while its EnvCell root remains
+                    // 0104. Applying the 1 cm margin calls that eye "inside"
+                    // 0106 and drops the entire look-in flood, exposing the
+                    // landscape/waterfall through half the cathedral.
+                    if (CameraOnInteriorSide(
+                            cell,
+                            i,
+                            cameraPos,
+                            SeedInPlaneEpsilon))
+                    {
+                        continue;
+                    }
                 }
 
                 float seedDistance = NearestPortalVertexDistance(poly, cell.WorldTransform, cameraPos);
@@ -741,6 +799,17 @@ public static class PortalVisibilityBuilder
                 if (clippedRegion.Count == 0)
                     continue;
 
+                // Preserve the exact CBldPortal that produced this view. The
+                // renderer must punch only accepted seed apertures; iterating
+                // every OtherCellId==0xFFFF portal on the reached cell turns a
+                // single accepted opening into unrelated far-depth holes.
+                var seedPortalView = frame.RentCellView();
+                AddRegion(seedPortalView, clippedRegion);
+                frame.ExteriorSeedPortals.Add(new ExteriorPortalSeed(
+                    cell.CellId,
+                    i,
+                    seedPortalView));
+
                 var seedView = GetOrCreate(frame, frame.CellViews, cell.CellId);
                 bool grew = AddRegion(seedView, clippedRegion);
 
@@ -1068,13 +1137,17 @@ public static class PortalVisibilityBuilder
     // InitCell leaves the in-plane case a CANDIDATE for cell portals (Ghidra
     // 0x005a4b70); building/exterior SEED portals additionally reject in-plane
     // via EyeInPlaneOfPortal (retail ConstructView(CBldPortal) IN_PLANE → 0).
-    private static bool CameraOnInteriorSide(LoadedCell cell, int portalIndex, Vector3 cameraPos)
+    private static bool CameraOnInteriorSide(
+        LoadedCell cell,
+        int portalIndex,
+        Vector3 cameraPos,
+        float epsilon = PortalSideEpsilon)
     {
         var plane = cell.ClipPlanes[portalIndex];
         if (plane.Normal.LengthSquared() < 1e-8f) return true; // no usable plane → allow
         var localCam = Vector3.Transform(cameraPos, cell.InverseWorldTransform);
         float dot = Vector3.Dot(plane.Normal, localCam) + plane.D;
-        return plane.InsideSide == 0 ? dot >= -PortalSideEpsilon : dot <= PortalSideEpsilon;
+        return plane.InsideSide == 0 ? dot >= -epsilon : dot <= epsilon;
     }
 
     // T2 (BR-4): retail ConstructView(CBldPortal)'s Sidedness IN_PLANE reject

src/AcDream.App/Rendering/RetailPViewPassExecutor.cs

@@ -134,6 +134,8 @@ internal sealed class RetailPViewPassExecutor :
     private readonly TerrainDrawDiagnosticsController _terrainDiagnostics;
     private readonly RetailPViewParticleClassifications _particleClassifications = new();
     private readonly HashSet<uint> _noSceneParticleEntityIds = [];
+    private readonly Dictionary<uint, int> _singleCellClipRouting = new(1);
+    private readonly Dictionary<uint, int> _noCellClipRouting = new(0);
 
     /// <summary>
     /// Borrowed until the next late landscape pass. The outdoor-root post-world
@@ -207,6 +209,8 @@ internal sealed class RetailPViewPassExecutor :
     {
         List<Exception>? failures = null;
         TryAbort(_frameGlState.RestoreFrameDefaults);
+        TryAbort(() => _envCells.SetClipRouting(null));
+        TryAbort(_entities.ClearClipRouting);
         TryAbort(_particleClassifications.BeginFrame);
         TryAbort(_noSceneParticleEntityIds.Clear);
         if (failures is { Count: > 0 })
@@ -230,6 +234,11 @@ internal sealed class RetailPViewPassExecutor :
         ClipFrameAssembly reuseAssembly) =>
         ClipFrameAssembler.Assemble(_clipFrame, portalFrame, reuseAssembly);
 
+    public void AppendLookInClipFrames(
+        IReadOnlyList<PortalVisibilityFrame> lookInFrames,
+        ClipFrameAssembly assembly) =>
+        ClipFrameAssembler.AppendLookInFrames(_clipFrame, lookInFrames, assembly);
+
     public void PrepareClipFrame(int terrainUploadCount) =>
         _surface.PrepareClipFrame(terrainUploadCount);
 
@@ -246,6 +255,24 @@ internal sealed class RetailPViewPassExecutor :
         _entities.ClearClipRouting();
     }
 
+    public void UseCellPortalViewRouting(uint cellId, ClipViewSlice slice)
+    {
+        _singleCellClipRouting.Clear();
+        _singleCellClipRouting.Add(cellId, slice.Slot);
+        _envCells.SetClipRouting(_singleCellClipRouting);
+        // Retail DrawMesh only viewcone-checks an object's sphere under the
+        // installed PortalList and then draws the mesh whole. Hard clipping the
+        // object here slices a stationary player when the chase camera crosses
+        // into the opposite cathedral cell while the player remains behind.
+        _entities.ClearClipRouting();
+    }
+
+    private void UseOutdoorPortalViewRouting(ClipViewSlice slice) =>
+        _entities.SetClipRouting(
+            _noCellClipRouting,
+            outdoorSlot: slice.Slot,
+            outdoorVisible: true);
+
     public void PrepareCellBatches(
         RetailPViewFrameInput frame,
         HashSet<uint> visibleCellIds) =>
@@ -376,6 +403,7 @@ internal sealed class RetailPViewPassExecutor :
 
         if (scissor)
             _surface.EndScissor();
+        _entities.ClearClipRouting();
         DisableClipDistances();
     }
 
@@ -418,8 +446,7 @@ internal sealed class RetailPViewPassExecutor :
 
         _particleClassifications.ReplaceOutdoor(context.ParticleOwnerIds);
 
-        if (!frame.RootCell.IsOutdoorNode
-            && _particleClassifications.Outdoor.Count > 0
+        if (_particleClassifications.Outdoor.Count > 0
             && _particles is not null
             && _particleRenderer is not null)
         {
@@ -427,7 +454,8 @@ internal sealed class RetailPViewPassExecutor :
                 frame.Camera,
                 frame.CameraWorldPosition,
                 ParticleRenderPass.Scene,
-                _particleClassifications.Outdoor);
+                _particleClassifications.Outdoor,
+                clipSlot: (uint)context.Slice.Slot);
         }
 
         EnableClipDistances();
@@ -456,6 +484,77 @@ internal sealed class RetailPViewPassExecutor :
 
         if (scissor)
             _surface.EndScissor();
+        _entities.ClearClipRouting();
+        DisableClipDistances();
+    }
+
+    public void DrawLandscapeStaticParticles(
+        RetailPViewFrameInput frame,
+        RetailPViewLandscapeStaticParticleContext context)
+    {
+        bool scissor = BeginDoorwayScissor(context.Slice.NdcAabb);
+        _surface.BindTerrainClip();
+        DisableClipDistances();
+
+        _particleClassifications.ReplaceOutdoor(context.ParticleOwnerIds);
+        if (_particleClassifications.Outdoor.Count > 0
+            && _particles is not null
+            && _particleRenderer is not null)
+        {
+            _particleRenderer.DrawForOwners(
+                frame.Camera,
+                frame.CameraWorldPosition,
+                ParticleRenderPass.Scene,
+                _particleClassifications.Outdoor,
+                clipSlot: (uint)context.Slice.Slot);
+        }
+
+        if (scissor)
+            _surface.EndScissor();
+        _entities.ClearClipRouting();
+        DisableClipDistances();
+    }
+
+    public void DrawLandscapeBuildingShellSlice(
+        RetailPViewFrameInput frame,
+        RetailPViewLandscapeBuildingShellSliceContext context)
+    {
+        UseOutdoorPortalViewRouting(context.Slice);
+        bool scissor = BeginDoorwayScissor(context.Slice.NdcAabb);
+        _surface.BindTerrainClip();
+        DisableClipDistances();
+
+        if (context.EntityDraw is RenderFrameEntityDrawRequest request)
+        {
+            RenderFrameView drawView = request.View;
+            _entities.DrawPackedProductionRoute(
+                frame.Camera,
+                in drawView,
+                request.Route,
+                request.RouteIndex,
+                request.CellId,
+                request.TupleLandblockId);
+        }
+        else if (context.BuildingShells.Count > 0)
+        {
+            var buildingEntry = (
+                frame.PlayerLandblockId ?? 0u,
+                Vector3.Zero,
+                Vector3.Zero,
+                context.BuildingShells,
+                (IReadOnlyDictionary<uint, WorldEntity>?)null);
+            _entities.Draw(
+                frame.Camera,
+                new[] { buildingEntry },
+                frame.Frustum,
+                neverCullLandblockId: frame.PlayerLandblockId,
+                visibleCellIds: null,
+                animatedEntityIds: frame.AnimatedEntityIds);
+        }
+
+        if (scissor)
+            _surface.EndScissor();
+        _entities.ClearClipRouting();
         DisableClipDistances();
     }
 
@@ -468,10 +567,13 @@ internal sealed class RetailPViewPassExecutor :
 
     public void DrawLookInPortalPunch(
         RetailPViewFrameInput frame,
-        RetailPViewCellSliceContext context) =>
-        DrawPortalDepthWrite(context, frame, forceFarZ: true);
+        RetailPViewCellSliceContext context,
+        int portalIndex) =>
+        DrawPortalDepthWrite(context, frame, forceFarZ: true, portalIndex);
 
-    public void DrawUnattachedSceneParticles(RetailPViewFrameInput frame)
+    public void DrawUnattachedSceneParticles(
+        RetailPViewFrameInput frame,
+        ClipViewSlice slice)
     {
         if (_particles is null || _particleRenderer is null)
             return;
@@ -482,7 +584,8 @@ internal sealed class RetailPViewPassExecutor :
             frame.CameraWorldPosition,
             ParticleRenderPass.Scene,
             _noSceneParticleEntityIds,
-            includeUnattached: true);
+            includeUnattached: true,
+            clipSlot: (uint)slice.Slot);
     }
 
     public void FlushLandscapeAlpha() => _alpha.Flush();
@@ -509,7 +612,8 @@ internal sealed class RetailPViewPassExecutor :
             frame.Camera,
             frame.CameraWorldPosition,
             ParticleRenderPass.Scene,
-            visible);
+            visible,
+            clipSlot: (uint)context.Slice.Slot);
         DisableClipDistances();
     }
 
@@ -552,7 +656,8 @@ internal sealed class RetailPViewPassExecutor :
     private void DrawPortalDepthWrite(
         RetailPViewCellSliceContext context,
         RetailPViewFrameInput frame,
-        bool forceFarZ)
+        bool forceFarZ,
+        int? onlyPortalIndex = null)
     {
         // Retail D3DPolyRender::DrawPortalPolyInternal @ 0x0059BC90.
         // Main interior roots stamp true depth (seal); outdoor and look-in
@@ -566,6 +671,8 @@ internal sealed class RetailPViewPassExecutor :
         Span<Vector3> world = stackalloc Vector3[32];
         for (int index = 0; index < cell.Portals.Count; index++)
         {
+            if (onlyPortalIndex.HasValue && index != onlyPortalIndex.Value)
+                continue;
             if (cell.Portals[index].OtherCellId != 0xFFFF)
                 continue;
             if (index >= cell.PortalPolygons.Count)

src/AcDream.App/Rendering/RetailPViewRenderer.cs

@@ -50,8 +50,10 @@ public sealed class RetailPViewRenderer
     private readonly Stack<PortalVisibilityFrame> _lookInFramePool = new();
     private readonly HashSet<uint> _lookInPrepareScratch = new();
 
-    // #131/#132: the late landscape phase's scene-particle owner survivors
-    // (statics + outside-stage dynamics passing the slice cone).
+    // #131/#132: landscape scene-particle owner survivors. With building
+    // look-ins, static owners use the pre-building alpha barrier and the late
+    // phase contains only outside-stage dynamics; otherwise the late phase
+    // carries both sets.
     private readonly HashSet<uint> _lateParticleOwnerScratch = new();
     private readonly HashSet<uint> _cellParticleOwnerScratch = new();
     private readonly HashSet<uint> _dynamicParticleOwnerScratch = new();
@@ -144,6 +146,7 @@ public sealed class RetailPViewRenderer
         var clipAssembly = passes.AssembleClipFrame(
             pvFrame,
             _clipAssemblyScratch);
+        passes.AppendLookInClipFrames(_lookInFrames, clipAssembly);
         int terrainUploadCount = checked(1 + clipAssembly.OutsideViewSlices.Length * 2);
         passes.PrepareClipFrame(terrainUploadCount);
 
@@ -413,6 +416,9 @@ public sealed class RetailPViewRenderer
                 group, ctx.ViewerEyePos, ctx.Cells.Find, ctx.ViewProjection,
                 OutdoorBuildingSeedDistance, pvFrame.OutsideView.Polygons,
                 reuseFrame: frameScratch);
+            LoadedCell sourceCell = group[0];
+            frame.SourceBuildingKey = sourceCell.BuildingId ?? sourceCell.CellId;
+            frame.SourceBuildingLandblockId = sourceCell.CellId & 0xFFFF0000u;
             if (frame.OrderedVisibleCells.Count > 0)
                 _lookInFrames.Add(frame);
             else
@@ -454,65 +460,67 @@ public sealed class RetailPViewRenderer
     // then draw the flooded cells' shells + statics far→near (the nested
     // DrawCells' DrawEnvCell + DrawObjCellForDummies; its outside_view is
     // empty by construction — PView ctor draw_landscape=0 — so no recursive
-    // landscape/clear/seal). Anything rasterized outside an aperture is
-    // repainted by the root's own shells after the depth clear, so over-draw
-    // here is color-safe; statics draw whole (the main viewcone has no entry
-    // for look-in cells; over-include is the safe direction).
+    // landscape/clear/seal). Retail CEnvCell::setup_view installs every cell's
+    // nested portal_view before DrawEnvCell, while DrawMesh iterates that same
+    // PortalList for cell objects. Preserve that per-slice gate here; drawing a
+    // nested cell whole lets its floor, details, and emitters escape the authored
+    // aperture even when the outer depth choreography is otherwise correct.
     private void DrawBuildingLookIns(
         RetailPViewFrameInput ctx,
         IRetailPViewPassExecutor passes,
         ClipFrameAssembly clipAssembly,
         InteriorEntityPartition.Result? partition,
+        ViewconeCuller viewcone,
         IRenderFrameEntityPassExecutor? frameEntityPasses,
         in RenderFrameView frameView)
     {
         if (_lookInFrames.Count == 0)
             return;
 
-        foreach (var frame in _lookInFrames)
+        int outsideSliceCount = clipAssembly.OutsideViewSlices.Length;
+        int lookInRouteIndex = 0;
+        for (int frameIndex = 0; frameIndex < _lookInFrames.Count; frameIndex++)
         {
+            PortalVisibilityFrame frame = _lookInFrames[frameIndex];
+
+            // Retail enters DrawBuilding once per building and drains every
+            // alpha submission accumulated by the preceding building before
+            // punching the next building's portals. The first building uses
+            // the pre-look-in barrier in DrawLandscapeThroughOutsideView.
+            if (frameIndex > 0)
+                passes.FlushLandscapeAlpha();
+
             // Pass 1: far-Z punch every aperture of this building.
-            foreach (uint cellId in frame.OrderedVisibleCells)
+            foreach (ExteriorPortalSeed seed in frame.ExteriorSeedPortals)
             {
-                if (!frame.CellViews.TryGetValue(cellId, out var view))
-                    continue;
-                foreach (var poly in view.Polygons)
+                foreach (var poly in seed.View.Polygons)
                 {
                     var cps = ClipPlaneSet.From(poly);
                     if (cps.IsNothingVisible)
                         continue;
                     passes.DrawLookInPortalPunch(ctx, new RetailPViewCellSliceContext(
-                        cellId,
+                        seed.CellId,
                         new ClipViewSlice(
                             0,
                             new Vector4(poly.MinX, poly.MinY, poly.MaxX, poly.MaxY),
                             cps.PlaneArray),
-                        NoParticleOwners));
+                        NoParticleOwners),
+                        seed.PortalIndex);
                 }
             }
 
-            // Pass 2: shells + statics, far→near.
-            passes.UseIndoorMembershipOnlyRouting();
-
-            // Opaque shells batched per building into ONE Render (this building's
-            // aperture punches above already ran; z-buffer handles order and
-            // lighting is per-instance CellId-keyed) — was one heavy per-frame
-            // Render per cell. Per-cell entity/particle work stays in the loop.
-            _shellBatch.Clear();
-            foreach (uint cid in frame.OrderedVisibleCells)
-                _shellBatch.Add(cid);
-            if (_shellBatch.Count > 0)
-                passes.DrawOpaqueCellShells(_shellBatch);
-
+            // Pass 2: shells + objects, far→near, once per portal_view slice.
             for (int i = frame.OrderedVisibleCells.Count - 1; i >= 0; i--)
             {
                 uint cellId = frame.OrderedVisibleCells[i];
-                _oneCell.Clear();
-                _oneCell.Add(cellId);
-                // Opaque shell batched above. Transparent stays per-cell (far→near)
-                // for correct compositing; skipped for opaque-only cells.
-                if (passes.CellHasTransparentShell(cellId))
-                    passes.DrawTransparentCellShells(_oneCell);
+                var clipKey = new LookInClipCell(frameIndex, cellId);
+                if (!clipAssembly.LookInCellToViewSlices.TryGetValue(
+                        clipKey,
+                        out ClipViewSlice[]? cellSlices)
+                    || cellSlices.Length == 0)
+                {
+                    continue;
+                }
 
                 _cellStaticScratch.Clear();
                 if (partition is not null
@@ -528,8 +536,7 @@ public sealed class RetailPViewRenderer
                 // post-clear they would z-fail against the root's seal anyway
                 // (the #118 lesson). Retail draws a look-in cell's objects
                 // inside the NESTED DrawCells (DrawObjCellForDummies,
-                // pc:432878+), i.e. right here in the landscape stage. Drawn
-                // WHOLE like the statics (AP-33's documented over-include).
+                // pc:432878+), i.e. right here in the landscape stage.
                 // No double-draw: dynamics-last keeps culling them (their
                 // cell is absent from the main cone), and their emitters ride
                 // the DrawCellParticles call below, not DrawDynamicsParticles
@@ -541,48 +548,154 @@ public sealed class RetailPViewRenderer
                             _cellStaticScratch.Add(e);
                 }
 
-                if (frameEntityPasses is not null)
+                foreach (ClipViewSlice slice in cellSlices)
                 {
-                    RenderFrameRouteOwnerSelector.Replace(
-                        _cellParticleOwnerScratch,
-                        in frameView,
-                        RenderFrameCandidateRoute.LookInObject,
-                        i,
-                        cellId);
-                }
-                else
-                {
-                    ReplaceOwnerIds(
-                        _cellParticleOwnerScratch,
-                        _cellStaticScratch);
-                }
+                    int routeIndex = lookInRouteIndex++;
+                    passes.UseCellPortalViewRouting(cellId, slice);
+                    _oneCell.Clear();
+                    _oneCell.Add(cellId);
+                    passes.DrawOpaqueCellShells(_oneCell);
+                    if (passes.CellHasTransparentShell(cellId))
+                        passes.DrawTransparentCellShells(_oneCell);
 
-                if (frameEntityPasses is not null
-                    || _cellStaticScratch.Count > 0)
-                {
-                    _candidateObserver?.ObservePViewBucket(
-                        CurrentRenderPViewRoute.LookInObject,
-                        i,
-                        cellId,
-                        _cellStaticScratch);
-                    DrawEntityRouteOrLegacy(
-                        ctx,
-                        passes,
-                        frameEntityPasses,
-                        in frameView,
-                        RenderFrameCandidateRoute.LookInObject,
-                        i,
-                        cellId,
-                        _cellStaticScratch,
-                        _oneCell);
+                    if (frameEntityPasses is not null)
+                    {
+                        RenderFrameRouteOwnerSelector.Replace(
+                            _cellParticleOwnerScratch,
+                            in frameView,
+                            RenderFrameCandidateRoute.LookInObject,
+                            routeIndex,
+                            cellId);
+                    }
+                    else
+                    {
+                        ReplaceOwnerIds(
+                            _cellParticleOwnerScratch,
+                            _cellStaticScratch);
+                    }
 
-                    // The cell-particles pass for look-in cells — retail's
-                    // nested DrawCells draws objects WITH their emitters.
-                    foreach (var slice in GetCellSlicesOrNoClip(clipAssembly, cellId))
+                    if (frameEntityPasses is not null
+                        || _cellStaticScratch.Count > 0)
+                    {
+                        _candidateObserver?.ObservePViewBucket(
+                            CurrentRenderPViewRoute.LookInObject,
+                            routeIndex,
+                            cellId,
+                            _cellStaticScratch);
+                        DrawEntityRouteOrLegacy(
+                            ctx,
+                            passes,
+                            frameEntityPasses,
+                            in frameView,
+                            RenderFrameCandidateRoute.LookInObject,
+                            routeIndex,
+                            cellId,
+                            _cellStaticScratch,
+                            _oneCell);
+
+                        // The nested DrawCells object pass includes emitters and
+                        // retains the exact setup_view clip until alpha playback.
                         passes.DrawCellParticles(ctx, new RetailPViewCellSliceContext(
                             cellId, slice, _cellParticleOwnerScratch));
+                    }
                 }
             }
+
+            // The ordinary exterior building shell is clipped by the outer
+            // outside_view, not by the nested cell PortalList.
+            passes.UseIndoorMembershipOnlyRouting();
+
+            // Retail's ordinary shell pass immediately follows this same
+            // building's portal-only pass. Pair by the shell's authored
+            // anchor EnvCell; never let an unrelated building repaint a
+            // look-in merely because both happen to be nearby.
+            int sliceIndex = 0;
+            foreach (ClipViewSlice slice in clipAssembly.OutsideViewSlices)
+            {
+                int shellRouteIndex = LookInBuildingShellRouteIndex(
+                    frameIndex,
+                    outsideSliceCount,
+                    sliceIndex);
+                _buildingShellScratch.Clear();
+                if (partition is not null)
+                {
+                    foreach (WorldEntity entity in partition.OutdoorStatic)
+                    {
+                        if (!entity.IsBuildingShell
+                            || FindLookInFrameIndex(
+                                entity.BuildingShellAnchorCellId ?? 0,
+                                _lookInFrames,
+                                ctx.Cells) != frameIndex)
+                        {
+                            continue;
+                        }
+
+                        EntitySphere(entity, out Vector3 center, out float radius);
+                        if (viewcone.SphereVisibleInOutsideSlice(
+                                sliceIndex,
+                                center,
+                                radius))
+                        {
+                            _buildingShellScratch.Add(entity);
+                        }
+                    }
+                }
+
+                _candidateObserver?.ObservePViewBucket(
+                    CurrentRenderPViewRoute.LandscapeBuildingShell,
+                    shellRouteIndex,
+                    0,
+                    _buildingShellScratch);
+                bool hasPackedShell = frameEntityPasses is not null
+                    && HasExactRoute(
+                        in frameView,
+                        RenderFrameCandidateRoute.LandscapeBuildingShell,
+                        shellRouteIndex,
+                        0);
+                if (hasPackedShell || _buildingShellScratch.Count > 0)
+                {
+                    RenderFrameEntityDrawRequest? shellDraw =
+                        frameEntityPasses is null
+                            ? null
+                            : new RenderFrameEntityDrawRequest(
+                                frameView,
+                                RenderFrameCandidateRoute.LandscapeBuildingShell,
+                                shellRouteIndex,
+                                0,
+                                ctx.PlayerLandblockId ?? 0);
+                    passes.DrawLandscapeBuildingShellSlice(
+                        ctx,
+                        new RetailPViewLandscapeBuildingShellSliceContext(
+                            slice,
+                            _buildingShellScratch)
+                        {
+                            EntityDraw = shellDraw,
+                        });
+
+                    _lateParticleOwnerScratch.Clear();
+                    if (frameEntityPasses is not null)
+                    {
+                        RenderFrameRouteOwnerSelector.Replace(
+                            _lateParticleOwnerScratch,
+                            in frameView,
+                            RenderFrameCandidateRoute.LandscapeBuildingShell,
+                            shellRouteIndex,
+                            0);
+                    }
+                    else
+                    {
+                        ReplaceOwnerIds(
+                            _lateParticleOwnerScratch,
+                            _buildingShellScratch);
+                    }
+                    passes.DrawLandscapeStaticParticles(
+                        ctx,
+                        new RetailPViewLandscapeStaticParticleContext(
+                            slice,
+                            _lateParticleOwnerScratch));
+                }
+                sliceIndex++;
+            }
         }
     }
 
@@ -598,18 +711,13 @@ public sealed class RetailPViewRenderer
         if (clipAssembly.OutsideViewSlices.Length == 0)
             return;
 
-        // #131/#132 (the FlushAlphaList deferral): retail collects ALL alpha
-        // draws of the landscape stage and flushes them ONCE after LScape::draw
-        // (D3DPolyRender::FlushAlphaList, DrawCells pc:432722) — so translucent
-        // landscape content (portal swirl meshes, flame particles) composites
-        // AFTER the building look-ins. Our dispatcher draws translucency inside
-        // each Draw call, so the stage is split in TWO phases instead: EARLY =
-        // sky + terrain + outdoor STATIC meshes (the look-in punches need their
-        // depth to mark against, the #117 lesson); then the look-ins; then
-        // LATE = outside-stage dynamics' meshes + ALL scene particles +
-        // weather. Content drawn early and overlapped by a look-in aperture
-        // was otherwise overpainted by the far interior (translucents write no
-        // depth to protect themselves) — the portal-swirl/candle-flame class.
+        // #131/#132: retail drains the remaining landscape alpha after
+        // LScape::draw (DrawCells pc:432720), while each DrawBuilding is also
+        // an earlier alpha barrier before its portal traversal (pc:427954).
+        // Our dispatcher batches outdoor content, so the stage is split into:
+        // EARLY sky/terrain/static meshes; an optional pre-look-in static-alpha
+        // barrier; building look-ins; then LATE outside-stage dynamics,
+        // remaining particles, and weather; followed by the outer flush.
         int probeSliceIndex = 0;
         foreach (var slice in clipAssembly.OutsideViewSlices)
         {
@@ -628,6 +736,14 @@ public sealed class RetailPViewRenderer
             {
                 foreach (var e in partition.OutdoorStatic)
                 {
+                    if (e.IsBuildingShell
+                        && FindLookInFrameIndex(
+                            e.BuildingShellAnchorCellId ?? 0,
+                            _lookInFrames,
+                            ctx.Cells) >= 0)
+                    {
+                        continue;
+                    }
                     EntitySphere(e, out var c, out float r);
                     if (viewcone.SphereVisibleInOutsideSlice(
                             probeSliceIndex,
@@ -663,15 +779,81 @@ public sealed class RetailPViewRenderer
                 });
         }
 
+        // Retail DrawBuilding flushes every alpha submission accumulated before
+        // the building immediately before its portal-only traversal
+        // (RenderDeviceD3D::DrawBuilding pc:427954-427956). That barrier is
+        // essential at open-air seams: foliage and static emitters encountered
+        // before the building must not be flushed after the look-in cell floor
+        // and repaint it. Our outdoor statics are one retained batch rather than
+        // retail's BSP-by-building walk, so use one barrier before the first
+        // look-in; DrawBuildingLookIns adds the corresponding barrier between
+        // each later building pair. Submit the early static owners' particles
+        // into the same alpha queue first; their mesh alpha was already
+        // submitted by the EARLY entity route above.
+        bool hasBuildingLookIns = _lookInFrames.Count > 0;
+        if (hasBuildingLookIns)
+        {
+            int barrierSliceIndex = 0;
+            foreach (var slice in clipAssembly.OutsideViewSlices)
+            {
+                // Ownerless outdoor emitters cannot ride an entity route. Retail
+                // draws their meshes once for every installed outside_view;
+                // retain that slot through deferred alpha playback.
+                passes.DrawUnattachedSceneParticles(ctx, slice);
+
+                _lateParticleOwnerScratch.Clear();
+                if (partition is not null)
+                {
+                    foreach (var e in partition.OutdoorStatic)
+                    {
+                        if (e.IsBuildingShell
+                            && FindLookInFrameIndex(
+                                e.BuildingShellAnchorCellId ?? 0,
+                                _lookInFrames,
+                                ctx.Cells) >= 0)
+                        {
+                            continue;
+                        }
+                        EntitySphere(e, out var c, out float r);
+                        if (viewcone.SphereVisibleInOutsideSlice(
+                                barrierSliceIndex,
+                                c,
+                                r))
+                        {
+                            _lateParticleOwnerScratch.Add(e.Id);
+                        }
+                    }
+                }
+                if (frameEntityPasses is not null)
+                {
+                    RenderFrameRouteOwnerSelector.Replace(
+                        _lateParticleOwnerScratch,
+                        in frameView,
+                        RenderFrameCandidateRoute.LandscapeOutdoorStatic,
+                        barrierSliceIndex,
+                        0);
+                }
+
+                passes.DrawLandscapeStaticParticles(
+                    ctx,
+                    new RetailPViewLandscapeStaticParticleContext(
+                        slice,
+                        _lateParticleOwnerScratch));
+                barrierSliceIndex++;
+            }
+            passes.FlushLandscapeAlpha();
+        }
+
         // #124: far-building look-ins draw HERE — still inside the landscape
         // stage (their punches mark against the terrain/exterior depth just
-        // drawn), strictly BEFORE the depth clear + seals below, matching
+        // drawn), strictly BEFORE the outer depth clear + seals below, matching
         // retail's LScape::draw placement (DrawCells pc:432719 vs 432732/432785).
         DrawBuildingLookIns(
             ctx,
             passes,
             clipAssembly,
             partition,
+            viewcone,
             frameEntityPasses,
             in frameView);
 
@@ -687,8 +869,8 @@ public sealed class RetailPViewRenderer
             passes.ClearClipRouting();
 
             _outdoorStaticScratch.Clear();      // late: dynamics survivors
-            _lateParticleOwnerScratch.Clear();  // late: statics + dynamics survivors
-            if (partition is not null)
+            _lateParticleOwnerScratch.Clear();  // late: dynamics, plus statics without look-ins
+            if (!hasBuildingLookIns && partition is not null)
             {
                 foreach (var e in partition.OutdoorStatic)
                 {
@@ -712,12 +894,19 @@ public sealed class RetailPViewRenderer
             }
             if (frameEntityPasses is not null)
             {
-                RenderFrameRouteOwnerSelector.Replace(
-                    _lateParticleOwnerScratch,
-                    in frameView,
-                    RenderFrameCandidateRoute.LandscapeOutdoorStatic,
-                    probeSliceIndex,
-                    0);
+                if (hasBuildingLookIns)
+                {
+                    _lateParticleOwnerScratch.Clear();
+                }
+                else
+                {
+                    RenderFrameRouteOwnerSelector.Replace(
+                        _lateParticleOwnerScratch,
+                        in frameView,
+                        RenderFrameCandidateRoute.LandscapeOutdoorStatic,
+                        probeSliceIndex,
+                        0);
+                }
                 RenderFrameRouteOwnerSelector.Union(
                     _lateParticleOwnerScratch,
                     in frameView,
@@ -753,13 +942,19 @@ public sealed class RetailPViewRenderer
 
         // #131: UNATTACHED emitters (AttachedObjectId == 0 — portal swirls,
         // campfires, ground effects anchored at a position) have no owner id
-        // to ride any of the id-filtered particle passes. The outdoor root
-        // has the dedicated T3 pass for them; an INTERIOR root had NO pass
-        // at all. Draw them ONCE per frame (not per slice — alpha particles
-        // must not double-draw, the #121 lesson), at the END of the landscape
-        // stage: after the clear they would z-fail against the doorway seal.
-        if (!ctx.RootCell.IsOutdoorNode)
-            passes.DrawUnattachedSceneParticles(ctx);
+        // to ride any of the id-filtered particle passes. Draw once per
+        // installed outside_view for BOTH root kinds, matching retail's
+        // landscape-stage placement and preserving the slot in each deferred
+        // draw. The former outdoor-root post-world tail ran after building
+        // cells and let exterior alpha repaint the cathedral transition.
+        // With no look-ins they drain at the end of the landscape stage; the
+        // look-in path submits them at its pre-building barrier so later opaque
+        // cell floors can cover them.
+        if (!hasBuildingLookIns)
+        {
+            foreach (ClipViewSlice slice in clipAssembly.OutsideViewSlices)
+                passes.DrawUnattachedSceneParticles(ctx, slice);
+        }
 
         // Retail PView::DrawCells 0x005A4872 drains the landscape alpha list
         // immediately after LScape::draw and before the optional depth clear.
@@ -779,6 +974,58 @@ public sealed class RetailPViewRenderer
         passes.UseIndoorMembershipOnlyRouting();
     }
 
+    internal static int LookInBuildingShellRouteIndex(
+        int frameIndex,
+        int outsideSliceCount,
+        int sliceIndex) =>
+        checked((frameIndex * outsideSliceCount) + sliceIndex);
+
+    internal static int FindLookInFrameIndex(
+        uint buildingShellAnchorCellId,
+        IReadOnlyList<PortalVisibilityFrame> lookInFrames,
+        IRetailPViewCellSource cells)
+    {
+        if (buildingShellAnchorCellId == 0)
+            return -1;
+
+        LoadedCell? anchorCell = cells.Find(buildingShellAnchorCellId);
+        if (anchorCell is null)
+            return -1;
+
+        uint buildingKey = anchorCell.BuildingId ?? anchorCell.CellId;
+        uint landblockId = anchorCell.CellId & 0xFFFF0000u;
+        for (int frameIndex = 0; frameIndex < lookInFrames.Count; frameIndex++)
+        {
+            PortalVisibilityFrame frame = lookInFrames[frameIndex];
+            if (frame.SourceBuildingKey == buildingKey
+                && frame.SourceBuildingLandblockId == landblockId)
+            {
+                return frameIndex;
+            }
+        }
+
+        return -1;
+    }
+
+    private static bool HasExactRoute(
+        in RenderFrameView view,
+        RenderFrameCandidateRoute route,
+        int routeIndex,
+        uint cellId)
+    {
+        foreach (RenderFrameCandidateRange range in view.RouteRanges)
+        {
+            if (range.Route == route
+                && range.RouteIndex == routeIndex
+                && range.CellId == cellId
+                && range.Count > 0)
+            {
+                return true;
+            }
+        }
+        return false;
+    }
+
     private void DrawExitPortalMasks(
         RetailPViewFrameInput ctx,
         IRetailPViewPassExecutor passes,
@@ -1180,6 +1427,7 @@ public sealed class RetailPViewRenderer
 
     // T3 scratch lists (render thread only; cleared per use).
     private readonly List<WorldEntity> _outdoorStaticScratch = new();
+    private readonly List<WorldEntity> _buildingShellScratch = new();
     private readonly List<WorldEntity> _cellStaticScratch = new();
     private readonly List<WorldEntity> _dynamicsScratch = new();
     // #118: dynamics assigned to the OUTSIDE stage this frame (interior roots
@@ -1343,10 +1591,14 @@ public interface IRetailPViewPassExecutor
     ClipFrameAssembly AssembleClipFrame(
         PortalVisibilityFrame portalFrame,
         ClipFrameAssembly reuseAssembly);
+    void AppendLookInClipFrames(
+        IReadOnlyList<PortalVisibilityFrame> lookInFrames,
+        ClipFrameAssembly assembly);
     void PrepareClipFrame(int terrainUploadCount);
     void SetTerrainClip(ReadOnlySpan<Vector4> planes);
     void ClearClipRouting();
     void UseIndoorMembershipOnlyRouting();
+    void UseCellPortalViewRouting(uint cellId, ClipViewSlice slice);
     void PrepareCellBatches(
         RetailPViewFrameInput frame,
         HashSet<uint> visibleCellIds);
@@ -1363,11 +1615,22 @@ public interface IRetailPViewPassExecutor
         ClipViewSlice slice,
         int sliceIndex);
     void DrawLandscapeSlice(RetailPViewFrameInput frame, RetailPViewLandscapeSliceContext context);
+    void DrawLandscapeStaticParticles(
+        RetailPViewFrameInput frame,
+        RetailPViewLandscapeStaticParticleContext context);
+    void DrawLandscapeBuildingShellSlice(
+        RetailPViewFrameInput frame,
+        RetailPViewLandscapeBuildingShellSliceContext context);
     void DrawLandscapeSliceLate(RetailPViewFrameInput frame, RetailPViewLandscapeLateSliceContext context);
     void ClearInteriorDepth();
     void DrawExitPortalMask(RetailPViewFrameInput frame, RetailPViewCellSliceContext context);
-    void DrawLookInPortalPunch(RetailPViewFrameInput frame, RetailPViewCellSliceContext context);
-    void DrawUnattachedSceneParticles(RetailPViewFrameInput frame);
+    void DrawLookInPortalPunch(
+        RetailPViewFrameInput frame,
+        RetailPViewCellSliceContext context,
+        int portalIndex);
+    void DrawUnattachedSceneParticles(
+        RetailPViewFrameInput frame,
+        ClipViewSlice slice);
     void FlushLandscapeAlpha();
     void DrawCellParticles(RetailPViewFrameInput frame, RetailPViewCellSliceContext context);
     void DrawDynamicsParticles(RetailPViewFrameInput frame, IReadOnlySet<uint> ownerIds);
@@ -1690,9 +1953,27 @@ public readonly record struct RetailPViewLandscapeSliceContext(
     internal RenderFrameEntityDrawRequest? EntityDraw { get; init; }
 }
 
+/// <summary>
+/// Outdoor-static emitters submitted at retail's pre-building alpha barrier.
+/// Mesh alpha for the same owners is already queued by the early landscape
+/// entity route.
+/// </summary>
+public readonly record struct RetailPViewLandscapeStaticParticleContext(
+    ClipViewSlice Slice,
+    IReadOnlySet<uint> ParticleOwnerIds);
+
+/// <summary>Retail DrawBuilding's ordinary exterior-shell pass, issued after
+/// the same building's portal-only look-in traversal.</summary>
+public readonly record struct RetailPViewLandscapeBuildingShellSliceContext(
+    ClipViewSlice Slice,
+    IReadOnlyList<WorldEntity> BuildingShells)
+{
+    internal RenderFrameEntityDrawRequest? EntityDraw { get; init; }
+}
+
 /// <summary>#131/#132: the late landscape phase's per-slice payload —
-/// outside-stage dynamics to mesh-draw, plus the full scene-particle owner
-/// set (statics + dynamics cone survivors) the attached-emitter filter keys on.</summary>
+/// outside-stage dynamics to mesh-draw, plus the particle owners not already
+/// submitted at a pre-building barrier.</summary>
 public readonly record struct RetailPViewLandscapeLateSliceContext(
     ClipViewSlice Slice,
     IReadOnlyList<WorldEntity> Dynamics,

src/AcDream.App/Rendering/Scene/CurrentRenderSceneOracle.cs

@@ -30,6 +30,7 @@ internal readonly record struct CurrentRenderProjectionFingerprint(
 internal enum CurrentRenderPViewRoute : byte
 {
     LandscapeOutdoorStatic,
+    LandscapeBuildingShell,
     LandscapeOutsideDynamic,
     LookInObject,
     CellStatic,

src/AcDream.App/Rendering/Scene/RenderFrameProduct.cs

@@ -13,6 +13,7 @@ internal enum RenderFrameBlendClass : byte
 internal enum RenderFrameCandidateRoute : byte
 {
     LandscapeOutdoorStatic,
+    LandscapeBuildingShell,
     LandscapeOutsideDynamic,
     LookInObject,
     CellStatic,

src/AcDream.App/Rendering/Scene/RenderScenePViewFrameProduct.cs

@@ -992,6 +992,8 @@ internal sealed class RenderScenePViewFrameProductController :
         {
             CurrentRenderPViewRoute.LandscapeOutdoorStatic =>
                 RenderFrameCandidateRoute.LandscapeOutdoorStatic,
+            CurrentRenderPViewRoute.LandscapeBuildingShell =>
+                RenderFrameCandidateRoute.LandscapeBuildingShell,
             CurrentRenderPViewRoute.LandscapeOutsideDynamic =>
                 RenderFrameCandidateRoute.LandscapeOutsideDynamic,
             CurrentRenderPViewRoute.LookInObject =>
@@ -1157,7 +1159,21 @@ internal sealed class RenderScenePViewFrameBuilder
             LoadSceneIndices(input.Scene);
 
             BuildOutdoorRoutes(writer, in input);
-            BuildLookInRoutes(writer, in input);
+            int lookInRouteIndex = 0;
+            for (int frameIndex = 0;
+                 frameIndex < input.LookInFrames.Count;
+                 frameIndex++)
+            {
+                BuildLookInRoutes(
+                    writer,
+                    in input,
+                    frameIndex,
+                    ref lookInRouteIndex);
+                BuildLookInBuildingShellRoutes(
+                    writer,
+                    in input,
+                    frameIndex);
+            }
             BuildOutsideDynamicRoutes(writer, in input);
             BuildCellStaticRoute(writer, in input);
             BuildDynamicLastRoute(writer, in input);
@@ -1279,6 +1295,14 @@ internal sealed class RenderScenePViewFrameBuilder
             for (int i = 0; i < _outdoorCount; i++)
             {
                 RenderProjectionRecord record = _outdoor[i];
+                if (record.EntityPayload.IsBuildingShell
+                    && RetailPViewRenderer.FindLookInFrameIndex(
+                        record.Source.BuildingShellAnchorCellId,
+                        input.LookInFrames,
+                        input.Cells) >= 0)
+                {
+                    continue;
+                }
                 Sphere(in record, out Vector3 center, out float radius);
                 if (!input.Viewcone.SphereVisibleInOutsideSlice(
                         sliceIndex,
@@ -1304,22 +1328,84 @@ internal sealed class RenderScenePViewFrameBuilder
         }
     }
 
+    private void BuildLookInBuildingShellRoutes(
+        RenderFrameWriter writer,
+        in RenderScenePViewBuildInput input,
+        int frameIndex)
+    {
+        int sliceCount = input.ClipAssembly.OutsideViewSlices.Length;
+        for (int sliceIndex = 0; sliceIndex < sliceCount; sliceIndex++)
+        {
+            int count = 0;
+            EnsureCapacity(ref _survivors, _outdoorCount);
+            for (int i = 0; i < _outdoorCount; i++)
+            {
+                RenderProjectionRecord record = _outdoor[i];
+                if (!record.EntityPayload.IsBuildingShell
+                    || RetailPViewRenderer.FindLookInFrameIndex(
+                        record.Source.BuildingShellAnchorCellId,
+                        input.LookInFrames,
+                        input.Cells) != frameIndex)
+                {
+                    continue;
+                }
+
+                Sphere(in record, out Vector3 center, out float radius);
+                if (!input.Viewcone.SphereVisibleInOutsideSlice(
+                        sliceIndex,
+                        in center,
+                        radius))
+                {
+                    continue;
+                }
+
+                _survivors[count++] = record;
+                writer.AddOutdoor(in record);
+                AddProjection(
+                    writer,
+                    in record,
+                    input.AnimatedEntityIds);
+            }
+
+            int routeIndex =
+                RetailPViewRenderer.LookInBuildingShellRouteIndex(
+                    frameIndex,
+                    sliceCount,
+                    sliceIndex);
+            writer.AddRouteRange(
+                RenderFrameCandidateRoute.LandscapeBuildingShell,
+                routeIndex,
+                0,
+                _survivors.AsSpan(0, count));
+        }
+    }
+
     private void BuildLookInRoutes(
         RenderFrameWriter writer,
-        in RenderScenePViewBuildInput input)
+        in RenderScenePViewBuildInput input,
+        int frameIndex,
+        ref int routeIndex)
     {
-        for (int frameIndex = 0;
-             frameIndex < input.LookInFrames.Count;
-             frameIndex++)
+        PortalVisibilityFrame frame = input.LookInFrames[frameIndex];
+        for (int i = frame.OrderedVisibleCells.Count - 1; i >= 0; i--)
         {
-            PortalVisibilityFrame frame = input.LookInFrames[frameIndex];
-            for (int i = frame.OrderedVisibleCells.Count - 1; i >= 0; i--)
+            uint cellId = frame.OrderedVisibleCells[i];
+            var clipKey = new LookInClipCell(frameIndex, cellId);
+            if (!input.ClipAssembly.LookInCellToViewSlices.TryGetValue(
+                    clipKey,
+                    out ClipViewSlice[]? slices)
+                || slices.Length == 0)
             {
-                uint cellId = frame.OrderedVisibleCells[i];
-                int count = LoadCell(
-                    input.Scene,
-                    cellId,
-                    includeDynamics: true);
+                continue;
+            }
+
+            int count = LoadCell(
+                input.Scene,
+                cellId,
+                includeDynamics: true);
+            for (int sliceIndex = 0; sliceIndex < slices.Length; sliceIndex++)
+            {
+                int currentRouteIndex = routeIndex++;
                 if (count == 0)
                     continue;
 
@@ -1330,7 +1416,7 @@ internal sealed class RenderScenePViewFrameBuilder
                         input.AnimatedEntityIds);
                 writer.AddRouteRange(
                     RenderFrameCandidateRoute.LookInObject,
-                    i,
+                    currentRouteIndex,
                     cellId,
                     _cell.AsSpan(0, count));
             }

src/AcDream.App/Rendering/Shaders/particle.vert

@@ -14,6 +14,23 @@ layout(location = 5) in vec4 aColor;
 // (ACDREAM_TEXTURE_HANDLE, injected by
 // tools/ShaderCompiler/VulkanGlslPreamble.cs).
 layout(location = 6) in uint aTextureIndex;
+layout(location = 7) in uint aClipSlot;
+
+struct CellClip {
+    uint count;
+    uint _p0;
+    uint _p1;
+    uint _p2;
+    vec4 planes[8];
+};
+layout(std430, binding = 2) readonly buffer ClipRegionBuf {
+    CellClip clipRegions[];
+};
+
+out gl_PerVertex {
+    vec4 gl_Position;
+    float gl_ClipDistance[8];
+};
 
 uniform mat4 uViewProjection;
 
@@ -35,4 +52,9 @@ void main() {
     // stage, which is the only form Vulkan can express.
     vTextureIndex = aTextureIndex;
     gl_Position = uViewProjection * vec4(world, 1.0);
+    CellClip clip = clipRegions[aClipSlot];
+    for (uint i = 0u; i < clip.count; ++i)
+        gl_ClipDistance[i] = dot(clip.planes[i], gl_Position);
+    for (uint i = clip.count; i < 8u; ++i)
+        gl_ClipDistance[i] = 1.0;
 }

src/AcDream.App/Rendering/Shaders/particle_mesh.vert

@@ -5,6 +5,23 @@ layout(location = 1) in vec3 aNormal;
 layout(location = 2) in vec2 aTexCoord;
 layout(location = 3) in mat4 aModel;
 layout(location = 7) in vec4 aColor;
+layout(location = 8) in uint aClipSlot;
+
+struct CellClip {
+    uint count;
+    uint _p0;
+    uint _p1;
+    uint _p2;
+    vec4 planes[8];
+};
+layout(std430, binding = 2) readonly buffer ClipRegionBuf {
+    CellClip clipRegions[];
+};
+
+out gl_PerVertex {
+    vec4 gl_Position;
+    float gl_ClipDistance[8];
+};
 
 uniform mat4 uViewProjection;
 
@@ -15,4 +32,9 @@ void main() {
     vTexCoord = aTexCoord;
     vColor = aColor;
     gl_Position = uViewProjection * aModel * vec4(aPosition, 1.0);
+    CellClip clip = clipRegions[aClipSlot];
+    for (uint i = 0u; i < clip.count; ++i)
+        gl_ClipDistance[i] = dot(clip.planes[i], gl_Position);
+    for (uint i = clip.count; i < 8u; ++i)
+        gl_ClipDistance[i] = 1.0;
 }

src/AcDream.App/Rendering/Shaders/spv/shaders.manifest.json

@@ -263,7 +263,7 @@
       "stages": [
         {
           "stage": "vert",
-          "sourceSha256": "921c32617708b3931a6304b4697ee96d728077d96f489d6c09eea4c5fe225b63",
+          "sourceSha256": "2bdd7114223164916a87e7d2e6df8a21fdcbd1cad082fafb3102b8a0fd4a2a8b",
           "compiled": true
         },
         {
@@ -279,7 +279,7 @@
       "stages": [
         {
           "stage": "vert",
-          "sourceSha256": "19db8757c1a61a2fbec8e56ce89d56b6dd6d66a123cedcdae40915af07d58c0e",
+          "sourceSha256": "582e9be4bca8bd1807d5a2152b211d1d4dd1ed54a6efe4240f52d402e628be75",
           "compiled": true
         },
         {

src/AcDream.App/Rendering/WorldRenderFrameBuilder.cs

@@ -43,6 +43,21 @@ internal readonly record struct WorldRootFrame(
     bool PlayerIndoorGate)
 {
     public bool RenderSky => ViewerRoot is null || RootSeenOutside;
+
+    /// <summary>
+    /// The camera has an EnvCell root whose authored visibility does not reach
+    /// outdoors. SeenOutside cells are open-air presentation cells, not an
+    /// indoor environment gate merely because they have portal geometry.
+    /// </summary>
+    public bool CameraInsideEnclosedCell => CameraInsideCell && !RootSeenOutside;
+
+    /// <summary>Environment gate shared by directional shadows and other
+    /// outdoor-only render-pack effects.</summary>
+    public bool PlayerOrCameraInsideEnclosedCell =>
+        PlayerInsideCell || CameraInsideEnclosedCell;
+
+    public bool IsAtmosphericallyOutdoor =>
+        RenderSky && !CameraInsideEnclosedCell;
 }
 
 /// <summary>Borrowed building scratch, valid only until the next build.</summary>

src/AcDream.App/Rendering/WorldScenePassExecutor.cs

@@ -221,17 +221,10 @@ internal sealed class WorldScenePassExecutor : IWorldScenePassExecutor
             return AppendSignature(currentSignature, "global");
         }
 
-        if (clipRoot.IsOutdoorNode)
-        {
-            _particleRenderer.DrawForOwners(
-                camera.Camera,
-                camera.Position,
-                ParticleRenderPass.Scene,
-                outdoorOwnerIds,
-                includeUnattached: true);
-            return AppendSignature(currentSignature, "unattached");
-        }
-
+        // Every PView root, including the outdoor sentinel, now submits scene
+        // particles inside LScape::draw. Replaying them here is both a duplicate
+        // and too late: it occurs after nested building cells, allowing exterior
+        // waterfall/foliage alpha to repaint an indoor/outdoor transition.
         return currentSignature;
     }
 

tests/AcDream.App.Tests/Rendering/ClipFrameAssemblerTests.cs

@@ -128,6 +128,39 @@ public class ClipFrameAssemblerTests
         Assert.Equal(TerrainClipMode.Planes, asm.TerrainMode);
     }
 
+    [Fact]
+    public void AppendLookInFrames_PacksEveryNestedCellViewWithoutReplacingMainRoutes()
+    {
+        const uint mainCell = 0xA9B40100;
+        const uint lookInCell = 0xA9B40106;
+        var main = new PortalVisibilityFrame();
+        main.CellViews[mainCell] = ViewOf(Square(0f, 0f, 0.8f));
+        main.OrderedVisibleCells.Add(mainCell);
+        main.OutsideView.Add(Square(0f, 0f, 0.7f));
+
+        var nested = new PortalVisibilityFrame();
+        nested.CellViews[lookInCell] = ViewOf(
+            Square(-0.35f, 0f, 0.15f),
+            Square(0.35f, 0f, 0.15f));
+        nested.OrderedVisibleCells.Add(lookInCell);
+
+        using ClipFrame frame = ClipFrame.NoClip();
+        ClipFrameAssembly assembly = ClipFrameAssembler.Assemble(frame, main);
+        int mainSlot = assembly.CellIdToSlot[mainCell];
+        int slotsBeforeLookIn = frame.SlotCount;
+
+        ClipFrameAssembler.AppendLookInFrames(frame, [nested], assembly);
+
+        var key = new LookInClipCell(0, lookInCell);
+        ClipViewSlice[] slices = assembly.LookInCellToViewSlices[key];
+        Assert.Equal(2, slices.Length);
+        Assert.All(slices, slice => Assert.True(slice.Slot >= slotsBeforeLookIn));
+        Assert.NotEqual(slices[0].Slot, slices[1].Slot);
+        Assert.Equal(slices[0].Slot, assembly.LookInCellToSlot[key]);
+        Assert.Equal(mainSlot, assembly.CellIdToSlot[mainCell]);
+        Assert.DoesNotContain(lookInCell, assembly.CellIdToSlot.Keys);
+    }
+
     [Fact]
     public void Assemble_OutsideViewWithExitPortal_HasOutsideViewTrue_AabbMatchesBounds()
     {

tests/AcDream.App.Tests/Rendering/Gpu/Vk/VulkanShaderManifestTests.cs

@@ -42,9 +42,12 @@ public sealed class VulkanShaderManifestTests
             ["mesh_modern.frag.spv"] = "b702b644862aca31ce1fb0677adc5872b39c4ea87f595a89363b44d10f2cc50e",
             ["mesh_modern.vert.spv"] = "7ca5fb241c4f0248884ba8fa88fbae17a7d5cbc80efe4ac4a9ffd0254012ead8",
             ["particle.frag.spv"] = "680da227704e0b3afa9b5226a7d73dd65aa9d8759d081cf4d5009d30e148726b",
-            ["particle.vert.spv"] = "ed79461ab347bf17edaca714bbbbfabead8192e059c760578ca3a1a01409799e",
+            // Re-pinned 2026-08-27: portal-view clip slots now travel with
+            // deferred billboard particles, matching retail PortalList draws.
+            ["particle.vert.spv"] = "bf0f6b7b26a6b237e4abb2973b9959a38338868fd8304b3863f593ad56d61c35",
             ["particle_mesh.frag.spv"] = "7696b1dc0613b5a724c55df465173f613ae047da9675895b149b7c71b009cc7c",
-            ["particle_mesh.vert.spv"] = "f7fe8b203cadcd4d54af5cdbcfd9d5bf733146e10bafa78ca730fb6970db0479",
+            // Same contract for full-mesh particle geometry.
+            ["particle_mesh.vert.spv"] = "b5b3e0f583e00b78b56e297e60e5050013a26b3a74dbec64f6e5b286b751f0fa",
             ["portal_depth.frag.spv"] = "96755196d4d0da7be4792107557465778be2ebefb5584834cc75bf90ec55a6cc",
             ["portal_depth.vert.spv"] = "cd113860b7acd6afad3ebcc0a68dd7147f6baae729df51ab360c123588dc3ae2",
             // sky.frag re-pinned 2026-08-23: the dome's fog blend lost its

tests/AcDream.App.Tests/Rendering/ParticleBindlessInstanceTests.cs

@@ -14,11 +14,15 @@ public sealed class ParticleBindlessInstanceTests
         // one TextureIndex (a binding=9 handle-table slot, 4 bytes), so the
         // struct shrank by 4 bytes; TextureIndex keeps TextureHandleLow's
         // former offset (64 — right after the four vec4 fields).
-        Assert.Equal(68, Marshal.SizeOf<ParticleRenderer.BillboardGpuInstance>());
+        Assert.Equal(72, Marshal.SizeOf<ParticleRenderer.BillboardGpuInstance>());
         Assert.Equal(
             new IntPtr(64),
             Marshal.OffsetOf<ParticleRenderer.BillboardGpuInstance>(
                 nameof(ParticleRenderer.BillboardGpuInstance.TextureIndex)));
+        Assert.Equal(
+            new IntPtr(68),
+            Marshal.OffsetOf<ParticleRenderer.BillboardGpuInstance>(
+                nameof(ParticleRenderer.BillboardGpuInstance.ClipSlot)));
     }
 
     [Fact]
@@ -40,6 +44,8 @@ public sealed class ParticleBindlessInstanceTests
         // index rather than by a null handle, because Vulkan's descriptor array
         // cannot be asked whether an element was ever written.
         Assert.Contains("layout(location = 6) in uint aTextureIndex;", vertex);
+        Assert.Contains("layout(location = 7) in uint aClipSlot;", vertex);
+        Assert.Contains("clipRegions[aClipSlot]", vertex);
         Assert.Contains("flat out uint vTextureIndex;", vertex);
         Assert.Contains("vTextureIndex = aTextureIndex;", vertex);
         Assert.Contains("#extension GL_ARB_bindless_texture : require", fragment);

tests/AcDream.App.Tests/Rendering/RenderScenePViewFrameProductTests.cs

@@ -21,6 +21,10 @@ public sealed class RenderScenePViewFrameProductTests
         RenderProjectionRecord outdoor = Record(
             0x0100_0000_0000_0001,
             RenderProjectionClass.OutdoorStatic);
+        RenderProjectionRecord buildingShell = Record(
+            0x0100_0000_0000_0008,
+            RenderProjectionClass.OutdoorStatic,
+            isBuildingShell: true);
         RenderProjectionRecord hidden = Record(
             0x0100_0000_0000_0002,
             RenderProjectionClass.OutdoorStatic,
@@ -48,6 +52,7 @@ public sealed class RenderScenePViewFrameProductTests
         RenderProjectionRecord[] records =
         [
             outdoor,
+            buildingShell,
             hidden,
             withdrawn,
             shell,
@@ -90,7 +95,7 @@ public sealed class RenderScenePViewFrameProductTests
         try
         {
             Assert.Equal(
-                [outdoor.Id, hidden.Id],
+                [outdoor.Id, hidden.Id, buildingShell.Id],
                 view.OutdoorStaticCandidates.ToArray()
                     .Select(static item => item.Id));
             Assert.Equal(
@@ -101,28 +106,42 @@ public sealed class RenderScenePViewFrameProductTests
                 [outdoorDynamic.Id, cellDynamic.Id],
                 view.DynamicCandidates.ToArray()
                     .Select(static item => item.Id));
-            Assert.Equal(5, view.Transforms.Length);
-            Assert.Equal(5, view.RouteCandidates.Length);
+            Assert.Equal(6, view.Transforms.Length);
+            Assert.Equal(6, view.RouteCandidates.Length);
             Assert.Equal(3, view.RouteRanges.Length);
+            RenderFrameCandidateRange outdoorRange = Assert.Single(
+                view.RouteRanges.ToArray(),
+                range => range.Route
+                    == RenderFrameCandidateRoute.LandscapeOutdoorStatic);
+            Assert.Equal(3, outdoorRange.Count);
+            Assert.Contains(
+                view.RouteCandidates.Slice(
+                    outdoorRange.Offset,
+                    outdoorRange.Count).ToArray(),
+                item => item.Id == buildingShell.Id);
+            Assert.DoesNotContain(
+                view.RouteRanges.ToArray(),
+                range => range.Route
+                    == RenderFrameCandidateRoute.LandscapeBuildingShell);
             Assert.DoesNotContain(
                 view.RouteCandidates.ToArray(),
                 item => item.Id == withdrawn.Id || item.Id == shell.Id);
             Assert.Equal(
                 new RenderFrameDiagnosticCounts(
-                    OutdoorStaticCandidates: 2,
+                    OutdoorStaticCandidates: 3,
                     CellStaticCandidates: 1,
                     DynamicCandidates: 2,
-                    TransformCount: 5,
+                    TransformCount: 6,
                     OpaqueClassificationCount: 0,
                     AlphaClassificationCount: 0,
                     LightSetCount: 0,
                     SelectionPartCount: 0,
-                    RouteCandidateCount: 5,
-                    EntityCandidateCount: 5,
-                    MeshPartCount: 5),
+                    RouteCandidateCount: 6,
+                    EntityCandidateCount: 6,
+                    MeshPartCount: 6),
                 view.DiagnosticCounts);
-            Assert.Equal(5, view.EntityCandidates.Length);
-            Assert.Equal(5, view.MeshParts.Length);
+            Assert.Equal(6, view.EntityCandidates.Length);
+            Assert.Equal(6, view.MeshParts.Length);
             Assert.Same(portal, view.PortalFrame);
             Assert.Same(clip, view.ClipAssembly);
             Assert.Equal(digest, view.SourceDigest);
@@ -133,6 +152,178 @@ public sealed class RenderScenePViewFrameProductTests
         }
     }
 
+    [Fact]
+    public void Builder_OrdersMultiSliceBuildingShellsAfterLookIns()
+    {
+        using var scene = new ArchRenderScene(Generation);
+        RenderProjectionRecord outdoor = Record(
+            0x0100_0000_0000_0101,
+            RenderProjectionClass.OutdoorStatic);
+        RenderProjectionRecord buildingShell = Record(
+            0x0100_0000_0000_0102,
+            RenderProjectionClass.OutdoorStatic,
+            isBuildingShell: true,
+            buildingShellAnchorCellId: Cell);
+        RenderProjectionRecord lookInObject = Record(
+            0x0100_0000_0000_0103,
+            RenderProjectionClass.IndoorCellStatic,
+            parentCell: Cell);
+        scene.Apply(
+        [
+            RenderProjectionDelta.Register(Generation, 1, outdoor),
+            RenderProjectionDelta.Register(Generation, 2, buildingShell),
+            RenderProjectionDelta.Register(Generation, 3, lookInObject),
+        ]);
+
+        PortalVisibilityFrame portal = Portal(Cell);
+        PortalVisibilityFrame lookIn = Portal(Cell);
+        lookIn.SourceBuildingKey = 2u;
+        lookIn.SourceBuildingLandblockId = Cell & 0xFFFF0000u;
+        var anchorCell = new LoadedCell
+        {
+            CellId = Cell,
+            BuildingId = 2u,
+        };
+        ClipFrameAssembly clip = TwoSliceClip(Cell);
+        clip.LookInCellToViewSlices[new LookInClipCell(0, Cell)] =
+            [clip.CellIdToViewSlices[Cell][0]];
+        ViewconeCuller viewcone =
+            ViewconeCuller.Build(clip, Matrix4x4.Identity);
+        var exchange = new RenderFrameExchange();
+        var builder = new RenderScenePViewFrameBuilder();
+        RenderSceneDigest digest =
+            scene.BuildDigest(new RenderSceneDigestBuffer());
+        var input = new RenderScenePViewBuildInput(
+            scene.OpenQuery(),
+            digest,
+            portal,
+            clip,
+            viewcone,
+            [lookIn],
+            [Cell],
+            new DictionaryCellSource(anchorCell),
+            [],
+            RootIsOutdoor: true);
+
+        builder.Build(exchange, frameSequence: 1, in input);
+        RenderFrameView view = exchange.BorrowLatest(Generation, 1);
+        try
+        {
+            Assert.Equal(
+            [
+                (RenderFrameCandidateRoute.LandscapeOutdoorStatic, 0, 0u),
+                (RenderFrameCandidateRoute.LandscapeOutdoorStatic, 1, 0u),
+                (RenderFrameCandidateRoute.LookInObject, 0, Cell),
+                (RenderFrameCandidateRoute.LandscapeBuildingShell, 0, 0u),
+                (RenderFrameCandidateRoute.LandscapeBuildingShell, 1, 0u),
+                (RenderFrameCandidateRoute.CellStatic, 0, 0u),
+            ],
+                view.RouteRanges.ToArray().Select(static range =>
+                    (range.Route, range.RouteIndex, range.CellId)));
+        }
+        finally
+        {
+            exchange.Release(in view);
+        }
+    }
+
+    [Fact]
+    public void Builder_InterleavesEachLookInWithItsOwnPackedBuildingShellRoutes()
+    {
+        const uint secondCell = 0xA9B40180u;
+        using var scene = new ArchRenderScene(Generation);
+        RenderProjectionRecord firstShell = Record(
+            0x0100_0000_0000_0201,
+            RenderProjectionClass.OutdoorStatic,
+            isBuildingShell: true,
+            buildingShellAnchorCellId: Cell);
+        RenderProjectionRecord secondShell = Record(
+            0x0100_0000_0000_0202,
+            RenderProjectionClass.OutdoorStatic,
+            isBuildingShell: true,
+            buildingShellAnchorCellId: secondCell);
+        RenderProjectionRecord firstObject = Record(
+            0x0100_0000_0000_0203,
+            RenderProjectionClass.IndoorCellStatic,
+            parentCell: Cell);
+        RenderProjectionRecord secondObject = Record(
+            0x0100_0000_0000_0204,
+            RenderProjectionClass.IndoorCellStatic,
+            parentCell: secondCell);
+        scene.Apply(
+        [
+            RenderProjectionDelta.Register(Generation, 1, firstShell),
+            RenderProjectionDelta.Register(Generation, 2, secondShell),
+            RenderProjectionDelta.Register(Generation, 3, firstObject),
+            RenderProjectionDelta.Register(Generation, 4, secondObject),
+        ]);
+
+        PortalVisibilityFrame portal = Portal(Cell);
+        PortalVisibilityFrame firstLookIn = Portal(Cell);
+        firstLookIn.SourceBuildingKey = 2u;
+        firstLookIn.SourceBuildingLandblockId = Cell & 0xFFFF0000u;
+        PortalVisibilityFrame secondLookIn = Portal(secondCell);
+        secondLookIn.SourceBuildingKey = 3u;
+        secondLookIn.SourceBuildingLandblockId = secondCell & 0xFFFF0000u;
+        var firstAnchor = new LoadedCell
+        {
+            CellId = Cell,
+            BuildingId = 2u,
+        };
+        var secondAnchor = new LoadedCell
+        {
+            CellId = secondCell,
+            BuildingId = 3u,
+        };
+        ClipFrameAssembly clip = TwoSliceClip(Cell);
+        clip.LookInCellToViewSlices[new LookInClipCell(0, Cell)] =
+            [clip.CellIdToViewSlices[Cell][0]];
+        clip.LookInCellToViewSlices[new LookInClipCell(1, secondCell)] =
+            [clip.CellIdToViewSlices[Cell][0]];
+        ViewconeCuller viewcone =
+            ViewconeCuller.Build(clip, Matrix4x4.Identity);
+        var exchange = new RenderFrameExchange();
+        var builder = new RenderScenePViewFrameBuilder();
+        RenderSceneDigest digest =
+            scene.BuildDigest(new RenderSceneDigestBuffer());
+        var input = new RenderScenePViewBuildInput(
+            scene.OpenQuery(),
+            digest,
+            portal,
+            clip,
+            viewcone,
+            [firstLookIn, secondLookIn],
+            [Cell],
+            new DictionaryCellSource(firstAnchor, secondAnchor),
+            [],
+            RootIsOutdoor: true);
+
+        builder.Build(exchange, frameSequence: 1, in input);
+        RenderFrameView view = exchange.BorrowLatest(Generation, 1);
+        try
+        {
+            Assert.Equal(
+            [
+                (RenderFrameCandidateRoute.LookInObject, 0, Cell),
+                (RenderFrameCandidateRoute.LandscapeBuildingShell, 0, 0u),
+                (RenderFrameCandidateRoute.LandscapeBuildingShell, 1, 0u),
+                (RenderFrameCandidateRoute.LookInObject, 1, secondCell),
+                (RenderFrameCandidateRoute.LandscapeBuildingShell, 2, 0u),
+                (RenderFrameCandidateRoute.LandscapeBuildingShell, 3, 0u),
+            ],
+                view.RouteRanges.ToArray()
+                    .Where(static range =>
+                        range.Route is RenderFrameCandidateRoute.LookInObject
+                            or RenderFrameCandidateRoute.LandscapeBuildingShell)
+                    .Select(static range =>
+                        (range.Route, range.RouteIndex, range.CellId)));
+        }
+        finally
+        {
+            exchange.Release(in view);
+        }
+    }
+
     [Fact]
     public void Builder_ReusesOrderedIndicesWhileRefreshingDirtyRecords()
     {
@@ -501,7 +692,9 @@ public sealed class RenderScenePViewFrameProductTests
         uint? parentCell = null,
         RenderProjectionFlags flags =
             RenderProjectionFlags.Draw
-            | RenderProjectionFlags.SpatiallyResident)
+            | RenderProjectionFlags.SpatiallyResident,
+        bool isBuildingShell = false,
+        uint buildingShellAnchorCellId = 0)
     {
         uint fullCellId = parentCell ?? Landblock;
         Matrix4x4 transform = Matrix4x4.Identity;
@@ -531,14 +724,14 @@ public sealed class RenderScenePViewFrameProductTests
                 SourceId: 1,
                 ParentCellId: parentCell ?? 0,
                 EffectCellId: 0,
-                BuildingShellAnchorCellId: 0,
+                BuildingShellAnchorCellId: buildingShellAnchorCellId,
                 TransformFingerprint: default,
                 GeometryFingerprint: default,
                 AppearanceFingerprint: default),
             new RenderEntityPayload(
                 [new MeshRef((uint)id, Matrix4x4.Identity)],
                 PaletteOverride: null,
-                IsBuildingShell: false));
+                IsBuildingShell: isBuildingShell));
     }
 
     private static WorldEntity Entity(
@@ -578,6 +771,22 @@ public sealed class RenderScenePViewFrameProductTests
         return assembly;
     }
 
+    private static ClipFrameAssembly TwoSliceClip(uint cellId)
+    {
+        var first = new ClipViewSlice(
+            Slot: 0,
+            NdcAabb: new Vector4(-1, -1, 0, 1),
+            Planes: []);
+        var second = new ClipViewSlice(
+            Slot: 1,
+            NdcAabb: new Vector4(0, -1, 1, 1),
+            Planes: []);
+        var assembly = new ClipFrameAssembly();
+        assembly.SetOutsideViewSlices([first, second]);
+        assembly.CellIdToViewSlices[cellId] = [first];
+        return assembly;
+    }
+
     private static (
         uint LandblockId,
         Vector3 AabbMin,
@@ -602,4 +811,15 @@ public sealed class RenderScenePViewFrameProductTests
 
         public LoadedCell? Find(uint cellId) => null;
     }
+
+    private sealed class DictionaryCellSource : IRetailPViewCellSource
+    {
+        private readonly Dictionary<uint, LoadedCell> _cells;
+
+        public DictionaryCellSource(params LoadedCell[] cells) =>
+            _cells = cells.ToDictionary(static cell => cell.CellId);
+
+        public LoadedCell? Find(uint cellId) =>
+            _cells.TryGetValue(cellId, out LoadedCell? cell) ? cell : null;
+    }
 }

tests/AcDream.App.Tests/Rendering/RetailPViewPassExecutorTests.cs

@@ -23,6 +23,7 @@ public sealed class RetailPViewPassExecutorTests
             [
                 "begin",
                 "assemble",
+                "append-look-in-clips",
                 "prepare-clip:3",
                 "indoor-routing",
                 "prepare-cells",
@@ -33,6 +34,7 @@ public sealed class RetailPViewPassExecutorTests
                 "terrain-clip",
                 "clear-routing",
                 "landscape-late",
+                "unattached-particles",
                 "landscape-alpha",
                 "indoor-routing",
                 "indoor-routing",
@@ -272,6 +274,88 @@ public sealed class RetailPViewPassExecutorTests
             executor);
 
         Assert.Contains("look-in-punch", executor.Operations);
+        AssertAppearsInOrder(
+            string.Join('|', executor.Operations),
+            "landscape-early",
+            "unattached-particles",
+            "landscape-static-particles",
+            "landscape-alpha",
+            "look-in-punch",
+            "landscape-late",
+            "landscape-alpha",
+            "interior-depth-clear");
+    }
+
+    [Fact]
+    public void DrawInside_repaints_the_exterior_building_shell_after_its_look_in()
+    {
+        var renderer = new RetailPViewRenderer();
+        using var executor = new RecordingExecutor();
+        LoadedCell root = InteriorWithExit(0xA9B40100u);
+        root.BuildingId = 1u;
+        LoadedCell[] building = NearbyTwoCellBuilding();
+        WorldEntity exteriorShell = Entity(
+            0x700u,
+            isBuildingShell: true,
+            buildingShellAnchorCellId: building[0].CellId);
+
+        renderer.DrawInside(
+            Frame(
+                root,
+                [exteriorShell],
+                nearbyBuildingCells: building,
+                additionalCells: building),
+            executor);
+
+        AssertAppearsInOrder(
+            string.Join('|', executor.Operations),
+            "landscape-early",
+            "look-in-punch",
+            "landscape-building-shell",
+            "landscape-late");
+    }
+
+    [Fact]
+    public void DrawInside_pairs_each_look_in_with_only_its_own_shell_and_alpha_barrier()
+    {
+        var renderer = new RetailPViewRenderer();
+        using var executor = new RecordingExecutor();
+        LoadedCell root = InteriorWithExit(0xA9B40100u);
+        root.BuildingId = 1u;
+        LoadedCell[] first = NearbyTwoCellBuilding();
+        LoadedCell[] second = NearbyTwoCellBuilding(
+            0xA9B40172u,
+            0xA9B40173u,
+            buildingId: 3u);
+        LoadedCell[] buildings = [.. first, .. second];
+        WorldEntity[] shells =
+        [
+            Entity(
+                0x700u,
+                isBuildingShell: true,
+                buildingShellAnchorCellId: first[0].CellId),
+            Entity(
+                0x701u,
+                isBuildingShell: true,
+                buildingShellAnchorCellId: second[0].CellId),
+        ];
+
+        renderer.DrawInside(
+            Frame(
+                root,
+                shells,
+                nearbyBuildingCells: buildings,
+                additionalCells: buildings),
+            executor);
+
+        AssertAppearsInOrder(
+            string.Join('|', executor.Operations),
+            "look-in-punch",
+            "landscape-building-shell",
+            "landscape-static-particles",
+            "landscape-alpha",
+            "look-in-punch",
+            "landscape-building-shell");
     }
 
     [Fact]
@@ -429,20 +513,21 @@ public sealed class RetailPViewPassExecutorTests
         return cell;
     }
 
-    private static LoadedCell[] NearbyTwoCellBuilding()
+    private static LoadedCell[] NearbyTwoCellBuilding(
+        uint vestibuleId = 0xA9B40170u,
+        uint roomId = 0xA9B40171u,
+        uint buildingId = 2u)
     {
-        const uint vestibuleId = 0xA9B40170u;
-        const uint roomId = 0xA9B40171u;
         var vestibule = new LoadedCell
         {
             CellId = vestibuleId,
-            BuildingId = 2u,
+            BuildingId = buildingId,
             WorldTransform = Matrix4x4.Identity,
             InverseWorldTransform = Matrix4x4.Identity,
             Portals =
             [
                 new CellPortalInfo(0xFFFF, 0, 0, 0),
-                new CellPortalInfo(0x0171, 1, 0, 0),
+                new CellPortalInfo((ushort)(roomId & 0xFFFFu), 1, 0, 0),
             ],
             ClipPlanes =
             [
@@ -472,10 +557,17 @@ public sealed class RetailPViewPassExecutorTests
         var room = new LoadedCell
         {
             CellId = roomId,
-            BuildingId = 2u,
+            BuildingId = buildingId,
             WorldTransform = Matrix4x4.Identity,
             InverseWorldTransform = Matrix4x4.Identity,
-            Portals = [new CellPortalInfo(0x0170, 0, 0, 1)],
+            Portals =
+            [
+                new CellPortalInfo(
+                    (ushort)(vestibuleId & 0xFFFFu),
+                    0,
+                    0,
+                    1),
+            ],
         };
         room.PortalPolygons.Add(
         [
@@ -490,7 +582,9 @@ public sealed class RetailPViewPassExecutorTests
     private static WorldEntity Entity(
         uint id,
         uint serverGuid = 0,
-        uint? parentCellId = null) => new()
+        uint? parentCellId = null,
+        bool isBuildingShell = false,
+        uint? buildingShellAnchorCellId = null) => new()
         {
             Id = id,
             ServerGuid = serverGuid,
@@ -499,6 +593,8 @@ public sealed class RetailPViewPassExecutorTests
             Rotation = Quaternion.Identity,
             MeshRefs = [new MeshRef(1u, Matrix4x4.Identity)],
             ParentCellId = parentCellId,
+            IsBuildingShell = isBuildingShell,
+            BuildingShellAnchorCellId = buildingShellAnchorCellId,
         };
 
     private static void AssertAppearsInOrder(string source, params string[] needles)
@@ -566,6 +662,17 @@ public sealed class RetailPViewPassExecutorTests
             return ClipFrameAssembler.Assemble(_clipFrame, portalFrame, reuseAssembly);
         }
 
+        public void AppendLookInClipFrames(
+            IReadOnlyList<PortalVisibilityFrame> lookInFrames,
+            ClipFrameAssembly assembly)
+        {
+            Operations.Add("append-look-in-clips");
+            ClipFrameAssembler.AppendLookInFrames(
+                _clipFrame,
+                lookInFrames,
+                assembly);
+        }
+
         public void PrepareClipFrame(int terrainUploadCount) =>
             Operations.Add($"prepare-clip:{terrainUploadCount}");
 
@@ -574,6 +681,8 @@ public sealed class RetailPViewPassExecutorTests
 
         public void ClearClipRouting() => Operations.Add("clear-routing");
         public void UseIndoorMembershipOnlyRouting() => Operations.Add("indoor-routing");
+        public void UseCellPortalViewRouting(uint cellId, ClipViewSlice slice) =>
+            Operations.Add($"cell-portal-routing:{cellId:X8}:{slice.Slot}");
         public void PrepareCellBatches(RetailPViewFrameInput frame, HashSet<uint> visibleCellIds) =>
             Operations.Add("prepare-cells");
         public void DrawOpaqueCellShells(HashSet<uint> cellIds) => Operations.Add("opaque-shells");
@@ -624,10 +733,37 @@ public sealed class RetailPViewPassExecutorTests
                     request.TupleLandblockId);
             }
         }
+
+        public void DrawLandscapeStaticParticles(
+            RetailPViewFrameInput frame,
+            RetailPViewLandscapeStaticParticleContext context) =>
+            Operations.Add("landscape-static-particles");
+        public void DrawLandscapeBuildingShellSlice(
+            RetailPViewFrameInput frame,
+            RetailPViewLandscapeBuildingShellSliceContext context)
+        {
+            Operations.Add("landscape-building-shell");
+            if (context.EntityDraw is RenderFrameEntityDrawRequest request)
+            {
+                RenderFrameView view = request.View;
+                DrawEntityRoute(
+                    frame.Camera,
+                    in view,
+                    request.Route,
+                    request.RouteIndex,
+                    request.CellId,
+                    request.TupleLandblockId);
+            }
+        }
         public void ClearInteriorDepth() => Operations.Add("interior-depth-clear");
         public void DrawExitPortalMask(RetailPViewFrameInput frame, RetailPViewCellSliceContext context) => Operations.Add("exit-mask");
-        public void DrawLookInPortalPunch(RetailPViewFrameInput frame, RetailPViewCellSliceContext context) => Operations.Add("look-in-punch");
-        public void DrawUnattachedSceneParticles(RetailPViewFrameInput frame) => Operations.Add("unattached-particles");
+        public void DrawLookInPortalPunch(
+            RetailPViewFrameInput frame,
+            RetailPViewCellSliceContext context,
+            int portalIndex) => Operations.Add("look-in-punch");
+        public void DrawUnattachedSceneParticles(
+            RetailPViewFrameInput frame,
+            ClipViewSlice slice) => Operations.Add("unattached-particles");
         public void FlushLandscapeAlpha() => Operations.Add("landscape-alpha");
         public void DrawCellParticles(RetailPViewFrameInput frame, RetailPViewCellSliceContext context) => Operations.Add("cell-particles");
         public void DrawDynamicsParticles(

tests/AcDream.App.Tests/Rendering/RhiVertexLayoutStrideTests.cs

@@ -105,10 +105,9 @@ public class RhiVertexLayoutStrideTests
             layout.StrideOf(0));
         Assert.Equal(GpuVertexInputRate.Vertex, layout.InputRateOf(0));
 
-        // Binding 1 is a mat4 model plus an RGBA colour, written as loose floats
-        // by WriteMeshGpuInstance.
+        // Binding 1 is the exact mesh-particle record: model, RGBA, clip slot.
         Assert.Equal(
-            (uint)(ParticleRenderer.MeshInstanceFloats * sizeof(float)),
+            (uint)Unsafe.SizeOf<ParticleRenderer.MeshParticleGpuInstance>(),
             layout.StrideOf(1));
         Assert.Equal(GpuVertexInputRate.Instance, layout.InputRateOf(1));
     }

tests/AcDream.App.Tests/Rendering/SanctuaryPortalSeamTests.cs

@@ -0,0 +1,226 @@
+using System.Collections.Generic;
+using System.Numerics;
+using AcDream.App.Rendering;
+using DatReaderWriter;
+using DatReaderWriter.DBObjs;
+using DatReaderWriter.Options;
+using Xunit;
+
+namespace AcDream.App.Tests.Rendering;
+
+/// <summary>
+/// Sanctuary cathedral seam captured 2026-08-27. The stationary player is in
+/// F4180104 while chase-camera zoom crosses the coincident outside portals at
+/// world Y=48 and the viewer root switches between two separate buildings:
+/// B3={0103,0104,0105} and B4={0106..0111}. The opposite cathedral half must
+/// remain available through the interior-root building look-in on both sides.
+/// </summary>
+[Trait("Lane", "InstalledDat")]
+public sealed class SanctuaryPortalSeamTests
+{
+    private const uint Landblock = 0xF4180000u;
+    private const uint Cell0104 = Landblock | 0x0104u;
+    private const uint Cell0106 = Landblock | 0x0106u;
+
+    private static Matrix4x4 ViewProjection(Vector3 eye)
+    {
+        // Derived from the two exact flap-sweep points. Extending their zoom
+        // ray reaches the stable chase target at the player's head.
+        var target = new Vector3(36.033f, 49.638f, 171.353f);
+        var view = Matrix4x4.CreateLookAt(eye, target, Vector3.UnitZ);
+        var projection = Matrix4x4.CreatePerspectiveFieldOfView(
+            1.2f, 893f / 522f, 1f, 5000f);
+        return view * projection;
+    }
+
+    private static IReadOnlyList<LoadedCell> Cells(
+        Dictionary<uint, LoadedCell> cells,
+        uint firstLow,
+        uint lastLow)
+    {
+        var result = new List<LoadedCell>();
+        for (uint low = firstLow; low <= lastLow; low++)
+            result.Add(cells[Landblock | low]);
+        return result;
+    }
+
+    [Fact]
+    public void CapturedZoomHandoff_BothRootsBuildTheExactOppositeCathedralSeed()
+    {
+        string? datDir = CornerFloodReplayTests.ResolveDatDir();
+        if (datDir is null)
+        {
+            Assert.Fail("Lane=InstalledDat requires an installed retail DAT directory; see docs/release-gate.md.");
+        }
+
+        using var dats = new DatCollection(datDir, DatAccessType.Read);
+        LandBlockInfo info = Assert.IsType<LandBlockInfo>(dats.Get<LandBlockInfo>(Landblock | 0xfffeu));
+        Dictionary<uint, LoadedCell> cells =
+            Issue120ReciprocalPingPongTests.LoadAllInteriorCells(dats, Landblock);
+        LoadedCell? Lookup(uint id) => cells.TryGetValue(id, out LoadedCell? cell) ? cell : null;
+
+        IReadOnlyList<LoadedCell> building3 = Cells(cells, 0x0103u, 0x0105u);
+        IReadOnlyList<LoadedCell> building4 = Cells(cells, 0x0106u, 0x0111u);
+        Assert.Equal(0x01001FB2u, info.Buildings[3].ModelId);
+        Assert.Equal(0x01001FB3u, info.Buildings[4].ModelId);
+
+        var captures = new[]
+        {
+            new
+            {
+                Name = "near/root0104",
+                Eye = new Vector3(32.742317f, 48.034306f, 172.447845f),
+                Root = cells[Cell0104],
+                Opposite = building4,
+                ExpectedOppositeCell = Cell0106,
+                ExpectedSeedPortal = 2,
+                OppositeBuildingIndex = 4,
+            },
+            new
+            {
+                Name = "far/root0106",
+                Eye = new Vector3(32.308865f, 47.823200f, 172.592255f),
+                Root = cells[Cell0106],
+                Opposite = building3,
+                ExpectedOppositeCell = Cell0104,
+                ExpectedSeedPortal = 0,
+                OppositeBuildingIndex = 3,
+            },
+        };
+
+        foreach (var capture in captures)
+        {
+            Matrix4x4 viewProjection = ViewProjection(capture.Eye);
+            PortalVisibilityFrame main = PortalVisibilityBuilder.Build(
+                capture.Root, capture.Eye, Lookup, viewProjection);
+            PortalVisibilityFrame lookIn = PortalVisibilityBuilder.ConstructViewBuilding(
+                capture.Opposite,
+                capture.Eye,
+                Lookup,
+                viewProjection,
+                maxSeedDistance: float.PositiveInfinity,
+                seedRegion: main.OutsideView.Polygons);
+
+            Assert.Contains(capture.ExpectedOppositeCell, lookIn.OrderedVisibleCells);
+            Assert.True(
+                lookIn.CellViews.TryGetValue(capture.ExpectedOppositeCell, out CellView? view)
+                && view.Polygons.Count > 0,
+                $"{capture.Name} must retain a clipped aperture for the opposite cathedral half");
+            ExteriorPortalSeed seed = Assert.Single(lookIn.ExteriorSeedPortals);
+            Assert.Equal(capture.ExpectedOppositeCell, seed.CellId);
+            Assert.Equal(capture.ExpectedSeedPortal, seed.PortalIndex);
+            Assert.NotEmpty(seed.View.Polygons);
+
+            using ClipFrame clipFrame = ClipFrame.NoClip();
+            ClipFrameAssembly assembly = ClipFrameAssembler.Assemble(
+                clipFrame,
+                main);
+            ClipFrameAssembler.AppendLookInFrames(
+                clipFrame,
+                [lookIn],
+                assembly);
+            ClipViewSlice[] nestedSlices =
+                assembly.LookInCellToViewSlices[
+                    new LookInClipCell(0, capture.ExpectedOppositeCell)];
+            Assert.Equal(view.Polygons.Count, nestedSlices.Length);
+            Assert.All(nestedSlices, slice => Assert.True(slice.Slot > 0));
+
+            Assert.Contains(
+                info.Buildings[capture.OppositeBuildingIndex].Portals,
+                portal => portal.OtherCellId == (capture.ExpectedOppositeCell & 0xffffu)
+                    && portal.OtherPortalId == capture.ExpectedSeedPortal);
+        }
+    }
+
+    [Fact]
+    public void ReportedLateralTransition_BothRootsKeepTheOppositeFacadePortal()
+    {
+        string? datDir = CornerFloodReplayTests.ResolveDatDir();
+        if (datDir is null)
+            Assert.Fail("Lane=InstalledDat requires an installed retail DAT directory.");
+
+        using var dats = new DatCollection(datDir, DatAccessType.Read);
+        Dictionary<uint, LoadedCell> cells =
+            Issue120ReciprocalPingPongTests.LoadAllInteriorCells(dats, Landblock);
+        LoadedCell? Lookup(uint id) => cells.TryGetValue(id, out LoadedCell? cell) ? cell : null;
+
+        static (PortalVisibilityFrame Main, PortalVisibilityFrame LookIn) Build(
+            Vector3 eye,
+            Vector3 target,
+            LoadedCell root,
+            IReadOnlyList<LoadedCell> opposite,
+            Func<uint, LoadedCell?> lookup)
+        {
+            Matrix4x4 viewProjection = Matrix4x4.CreateLookAt(eye, target, Vector3.UnitZ)
+                * Matrix4x4.CreatePerspectiveFieldOfView(MathF.PI / 3f, 1.6f, 0.1f, 5000f);
+            PortalVisibilityFrame main = PortalVisibilityBuilder.Build(
+                root, eye, lookup, viewProjection);
+            PortalVisibilityFrame lookIn = PortalVisibilityBuilder.ConstructViewBuilding(
+                opposite, eye, lookup, viewProjection, seedRegion: main.OutsideView.Polygons);
+            return (main, lookIn);
+        }
+
+        (PortalVisibilityFrame Main, PortalVisibilityFrame LookIn) from0106 = Build(
+                new Vector3(31.189594f, 46.280170f, 171.783646f),
+                new Vector3(32.787731f, 46.275948f, 171.354993f),
+                cells[Cell0106],
+                Cells(cells, 0x0103u, 0x0105u),
+                Lookup);
+        (PortalVisibilityFrame Main, PortalVisibilityFrame LookIn) from0104 = Build(
+                new Vector3(31.198704f, 49.733287f, 171.783646f),
+                new Vector3(32.796841f, 49.729065f, 171.354993f),
+                cells[Cell0104],
+                Cells(cells, 0x0106u, 0x0111u),
+                Lookup);
+
+        Assert.Equal([Cell0106, Landblock | 0x010Fu], from0106.Main.OrderedVisibleCells);
+        Assert.Equal([Cell0104], from0106.LookIn.OrderedVisibleCells);
+        ExteriorPortalSeed seed0104 = Assert.Single(from0106.LookIn.ExteriorSeedPortals);
+        Assert.Equal(Cell0104, seed0104.CellId);
+        Assert.Equal(0, seed0104.PortalIndex);
+        Assert.NotEmpty(seed0104.View.Polygons);
+
+        Assert.Equal([Cell0104], from0104.Main.OrderedVisibleCells);
+        Assert.Equal([Cell0106, Landblock | 0x010Fu], from0104.LookIn.OrderedVisibleCells);
+        ExteriorPortalSeed seed0106 = Assert.Single(from0104.LookIn.ExteriorSeedPortals);
+        Assert.Equal(Cell0106, seed0106.CellId);
+        Assert.Equal(2, seed0106.PortalIndex);
+        Assert.NotEmpty(seed0106.View.Polygons);
+    }
+
+    [Fact]
+    public void ReportedExactSteamSeam_Root0104KeepsTheOppositeCathedralPortal()
+    {
+        string? datDir = CornerFloodReplayTests.ResolveDatDir();
+        if (datDir is null)
+            Assert.Fail("Lane=InstalledDat requires an installed retail DAT directory.");
+
+        using var dats = new DatCollection(datDir, DatAccessType.Read);
+        Dictionary<uint, LoadedCell> cells =
+            Issue120ReciprocalPingPongTests.LoadAllInteriorCells(dats, Landblock);
+        LoadedCell? Lookup(uint id) => cells.TryGetValue(id, out LoadedCell? cell) ? cell : null;
+
+        // Live ACDREAM_PROBE_CELL capture for the user-reported stationary
+        // frame at player [32.792290, 48.000618, 169.804993]. The chase eye is
+        // only ~4 mm across the coincident 0104/0106 exterior portal plane.
+        var eye = new Vector3(31.189665f, 48.004852f, 171.784988f);
+        var target = new Vector3(32.792290f, 48.000618f, 171.354993f);
+        Matrix4x4 viewProjection = Matrix4x4.CreateLookAt(eye, target, Vector3.UnitZ)
+            * Matrix4x4.CreatePerspectiveFieldOfView(1.2f, 1555f / 1019f, 1f, 5000f);
+
+        PortalVisibilityFrame main = PortalVisibilityBuilder.Build(
+            cells[Cell0104], eye, Lookup, viewProjection);
+        PortalVisibilityFrame lookIn = PortalVisibilityBuilder.ConstructViewBuilding(
+            Cells(cells, 0x0106u, 0x0111u),
+            eye,
+            Lookup,
+            viewProjection,
+            seedRegion: main.OutsideView.Polygons);
+
+        Assert.Contains(Cell0106, lookIn.OrderedVisibleCells);
+        ExteriorPortalSeed seed = Assert.Single(lookIn.ExteriorSeedPortals);
+        Assert.Equal(Cell0106, seed.CellId);
+        Assert.Equal(2, seed.PortalIndex);
+        Assert.NotEmpty(seed.View.Polygons);
+    }
+}

tests/AcDream.App.Tests/Rendering/WorldRenderFrameBuilderTests.cs

@@ -213,6 +213,9 @@ public sealed class WorldRenderFrameBuilderTests
             Assert.False(result.PlayerSeenOutside);
             Assert.True(result.RootSeenOutside);
             Assert.True(result.RenderSky);
+            Assert.False(result.CameraInsideEnclosedCell);
+            Assert.True(result.PlayerOrCameraInsideEnclosedCell);
+            Assert.True(result.IsAtmosphericallyOutdoor);
             Assert.Equal(playerCellId, result.PlayerCellId);
             Assert.Equal(viewerCellId, result.ViewerCellId);
             Assert.Equal(camera.Position, result.ViewerEyePosition);
@@ -245,6 +248,9 @@ public sealed class WorldRenderFrameBuilderTests
         Assert.False(result.PlayerInsideCell);
         Assert.False(result.CameraInsideCell);
         Assert.True(result.RenderSky);
+        Assert.False(result.CameraInsideEnclosedCell);
+        Assert.False(result.PlayerOrCameraInsideEnclosedCell);
+        Assert.True(result.IsAtmosphericallyOutdoor);
     }
 
     [Fact]

tests/AcDream.App.Tests/Rendering/WorldSceneRendererTests.cs

@@ -290,7 +290,7 @@ public sealed class WorldSceneRendererTests
         WorldRenderFrameOutcome result = rig.Renderer.Render(default);
 
         Assert.True(result.NormalWorldDrawn);
-        Assert.Contains("particles:pviewScoped+unattached", rig.Calls);
+        Assert.Contains("particles:pviewScoped", rig.Calls);
         Assert.Same(rig.PView.OutdoorSceneParticleEntityIds, rig.Passes.ParticleOwners);
         Assert.Equal([0xCAFEu], rig.Passes.ParticleOwners);
         Assert.DoesNotContain("flat:weather", rig.Calls);
@@ -809,9 +809,7 @@ public sealed class WorldSceneRendererTests
             string kind = clipRoot switch
             {
                 null => "global",
-                { IsOutdoorNode: true } => currentSignature == "none"
-                    ? "unattached"
-                    : currentSignature + "+unattached",
+                { IsOutdoorNode: true } => currentSignature,
                 _ => currentSignature,
             };
             calls.Add($"particles:{kind}");