diff --git a/src/AcDream.App/Rendering/RetailPViewRenderer.cs b/src/AcDream.App/Rendering/RetailPViewRenderer.cs
index c3eacb08..a8209b6c 100644
--- a/src/AcDream.App/Rendering/RetailPViewRenderer.cs
+++ b/src/AcDream.App/Rendering/RetailPViewRenderer.cs
@@ -71,6 +71,10 @@ public sealed class RetailPViewRenderer
     private readonly HashSet<uint> _cellParticleOwnerScratch = new();
     private readonly HashSet<uint> _dynamicParticleOwnerScratch = new();
 
+    // The walk's TRUE root flood as a set, rebuilt per frame for the
+    // DynamicLast stage gate (the stage-set split — synthesis plan step 4).
+    private readonly HashSet<uint> _rootFloodSetScratch = new();
+
     // MP-Alloc (2026-07-05): the frame's entity partition (ByCell/OutdoorStatic/
     // Dynamics), reused across frames instead of `new`ing a Result (a Dictionary
     // + 2 Lists, plus one List<WorldEntity> per visible cell) every DrawInside
@@ -507,6 +511,16 @@ public sealed class RetailPViewRenderer
             HashSet<uint> outsideStageFlood =
                 walkActive ? walkDriver!.VisitedCells : drawableCells;
 
+            // The stage-set split: the walk's TRUE root flood (never the
+            // visited union) keys which interior-parented dynamics may ride
+            // the last pass — see BuildOutsideDynamicRoutes' sibling gate.
+            _rootFloodSetScratch.Clear();
+            if (walkActive)
+            {
+                foreach (uint cellId in walkDriver!.InteriorFloodCells)
+                    _rootFloodSetScratch.Add(cellId);
+            }
+
             if (_sceneFrameProduct is not null)
             {
                 frameView = _sceneFrameProduct.BuildAndBorrow(
@@ -517,7 +531,11 @@ public sealed class RetailPViewRenderer
                     outsideStageFlood,
                     ctx.Cells,
                     ctx.AnimatedEntityIds,
-                    ctx.RootCell.IsOutdoorNode);
+                    ctx.RootCell.IsOutdoorNode,
+                    // Non-walk frames (diagnostic fakes / legacy fallback)
+                    // keep the pre-split admission: drawableCells WAS the
+                    // flood in the legacy meaning.
+                    walkActive ? _rootFloodSetScratch : drawableCells);
                 frameViewBorrowed = true;
                 frameEntityPasses!.BeginEntityFrame(in frameView);
                 entityFrameOpen = true;
diff --git a/src/AcDream.App/Rendering/Scene/RenderScenePViewFrameProduct.cs b/src/AcDream.App/Rendering/Scene/RenderScenePViewFrameProduct.cs
index b4495fbd..451a8b34 100644
--- a/src/AcDream.App/Rendering/Scene/RenderScenePViewFrameProduct.cs
+++ b/src/AcDream.App/Rendering/Scene/RenderScenePViewFrameProduct.cs
@@ -13,7 +13,8 @@ internal readonly record struct RenderScenePViewBuildInput(
     HashSet<uint> DrawableCells,
     IRetailPViewCellSource Cells,
     HashSet<uint>? AnimatedEntityIds,
-    bool RootIsOutdoor);
+    bool RootIsOutdoor,
+    IReadOnlySet<uint> RootFloodCells);
 
 internal readonly record struct RenderFrameProductComparisonSnapshot(
     bool Enabled,
@@ -188,7 +189,8 @@ internal sealed class RenderScenePViewFrameProductController :
         HashSet<uint> drawableCells,
         IRetailPViewCellSource cells,
         HashSet<uint>? animatedEntityIds,
-        bool rootIsOutdoor)
+        bool rootIsOutdoor,
+        IReadOnlySet<uint> rootFloodCells)
     {
         ArgumentNullException.ThrowIfNull(portalFrame);
         ArgumentNullException.ThrowIfNull(clipAssembly);
@@ -215,7 +217,8 @@ internal sealed class RenderScenePViewFrameProductController :
             drawableCells,
             cells,
             animatedEntityIds,
-            rootIsOutdoor);
+            rootIsOutdoor,
+            rootFloodCells);
         _builder.Build(_exchange, frameSequence, in input);
         return _exchange.BorrowLatest(
             scene.Generation,
@@ -235,8 +238,12 @@ internal sealed class RenderScenePViewFrameProductController :
         HashSet<uint>? animatedEntityIds,
         uint tupleLandblockId,
         bool rootIsOutdoor,
-        Vector3 cameraWorldPosition = default)
+        Vector3 cameraWorldPosition = default,
+        IReadOnlySet<uint>? rootFloodCells = null)
     {
+        // Comparison/diagnostic path: absent an explicit walk root flood,
+        // drawableCells keeps the pre-stage-split admission (drawableCells
+        // WAS the flood in the legacy meaning these fixtures pin).
         RenderFrameView view = BuildAndBorrow(
             portalFrame,
             clipAssembly,
@@ -245,7 +252,8 @@ internal sealed class RenderScenePViewFrameProductController :
             drawableCells,
             cells,
             animatedEntityIds,
-            rootIsOutdoor);
+            rootIsOutdoor,
+            rootFloodCells ?? drawableCells);
         try
         {
             Compare(
@@ -1417,6 +1425,33 @@ internal sealed class RenderScenePViewFrameBuilder
                 continue;
             }
 
+            // The stage-set split (synthesis plan step 4, [dyn-route]-pinned
+            // 2026-08-30): an interior-parented dynamic rides the LAST pass
+            // ONLY when its parent cell is in THE WALK'S OWN ROOT FLOOD.
+            // Retail draws a look-in cell's occupants inside the landscape
+            // stage through the composed portal chain, and an unreachable
+            // cell's occupants not at all — the legacy visibility builder
+            // invents cross-building cell views at the cathedral (real
+            // 3-5-plane cones for 0xF4180112 from roots with no sightline),
+            // which let a remote player draw post-clear/post-world through
+            // opaque walls. The walk's flood is oracle-trace-conformant;
+            // key the route on it.
+            if (indoor && !input.RootFloodCells.Contains(parentCellId!.Value))
+            {
+                if (AcDream.Core.Rendering.RenderingDiagnostics.ProbeWalkRootEnabled)
+                {
+                    string state = $"parent={parentCellId.Value:x8} rootflood-excluded";
+                    if (!_probeDynRouteStates.TryGetValue(record.Source.LocalEntityId, out string? prev)
+                        || prev != state)
+                    {
+                        _probeDynRouteStates[record.Source.LocalEntityId] = state;
+                        Console.WriteLine(
+                            $"[dyn-route] id={record.Source.LocalEntityId:x} {state}");
+                    }
+                }
+                continue;
+            }
+
             Sphere(in record, out Vector3 center, out float radius);
             bool visible = indoor
                 ? input.Viewcone.SphereVisibleInCell(
diff --git a/tests/AcDream.App.Tests/Rendering/RenderScenePViewFrameProductTests.cs b/tests/AcDream.App.Tests/Rendering/RenderScenePViewFrameProductTests.cs
index 86b08063..eba4ea90 100644
--- a/tests/AcDream.App.Tests/Rendering/RenderScenePViewFrameProductTests.cs
+++ b/tests/AcDream.App.Tests/Rendering/RenderScenePViewFrameProductTests.cs
@@ -162,7 +162,8 @@ public sealed class RenderScenePViewFrameProductTests
                 [Cell],
                 EmptyCellSource.Instance,
                 [],
-                RootIsOutdoor: true);
+                RootIsOutdoor: true,
+                RootFloodCells: new HashSet<uint> { Cell });
             builder.Build(exchange, frameSequence, in input);
         }
     }