diff --git a/src/AcDream.App/Rendering/GameWindow.cs b/src/AcDream.App/Rendering/GameWindow.cs
index 1c1db412..c96ad05f 100644
--- a/src/AcDream.App/Rendering/GameWindow.cs
+++ b/src/AcDream.App/Rendering/GameWindow.cs
@@ -5630,25 +5630,46 @@ public sealed class GameWindow : IDisposable
                     // as WorldEntity records below — they have real GfxObj MeshRefs that work
                     // fine; EnvCellRenderer.RegisterCell receives an empty staticObjects list.
                     var cellSubMeshes = AcDream.Core.Meshing.CellMesh.Build(envCell, cellStruct, _dats);
+
+                    // The cell transforms and the physics + visibility hydration are
+                    // INDEPENDENT of whether the cell has drawable geometry. Retail
+                    // couples neither collision nor portal visibility to a render mesh.
+                    // Keep the small render lift out of physics; retail BSP contact
+                    // planes use the EnvCell origin verbatim. The lift constant is
+                    // shared with every draw-space consumer of portal polygons
+                    // (OutsideView gate, seal/punch fans) — see
+                    // PortalVisibilityBuilder.ShellDrawLiftZ (#130).
+                    var physicsCellOrigin = envCell.Position.Origin + lbOffset;
+                    var cellOrigin = physicsCellOrigin + new System.Numerics.Vector3(
+                        0f, 0f, AcDream.App.Rendering.PortalVisibilityBuilder.ShellDrawLiftZ);
+                    var cellTransform =
+                        System.Numerics.Matrix4x4.CreateFromQuaternion(envCell.Position.Orientation) *
+                        System.Numerics.Matrix4x4.CreateTranslation(cellOrigin);
+                    var physicsCellTransform =
+                        System.Numerics.Matrix4x4.CreateFromQuaternion(envCell.Position.Orientation) *
+                        System.Numerics.Matrix4x4.CreateTranslation(physicsCellOrigin);
+
+                    // G.3a (#133) hydration decouple: BuildLoadedCell + CacheCellStruct
+                    // were previously gated behind `cellSubMeshes.Count > 0`, which
+                    // silently dropped collision (CellTransit.GetCellStruct -> null ->
+                    // fall through floor) and the visibility node for any geometry-less
+                    // collision cell. CacheCellStruct self-gates on a null PhysicsBSP
+                    // (PhysicsDataCache), so this is safe for cells with no physics.
+                    //
+                    // BuildLoadedCell uses the PHYSICS (unlifted) transform. The +0.02 m
+                    // render lift above is a DRAW concern (shell z-fighting vs terrain);
+                    // feeding it into the visibility graph shifted every HORIZONTAL portal
+                    // plane 2 cm up, side-culling decks/landings (#119-residual,
+                    // TowerAscentReplayTests.CapturedTopOfStairs_*). Vertical doorways were
+                    // immune (the lift slides their planes along themselves).
+                    BuildLoadedCell(envCellId, envCell, cellStruct, physicsCellOrigin, physicsCellTransform);
+                    _physicsDataCache.CacheCellStruct(envCellId, envCell, cellStruct, physicsCellTransform);
+
+                    // Render registration only when the cell actually has drawable submeshes.
                     if (cellSubMeshes.Count > 0)
                     {
                         _pendingCellMeshes[envCellId] = cellSubMeshes;
 
-                        // Keep the small render lift out of physics; retail BSP
-                        // contact planes use the EnvCell origin verbatim. The lift
-                        // constant is shared with every draw-space consumer of
-                        // portal polygons (OutsideView gate, seal/punch fans) —
-                        // see PortalVisibilityBuilder.ShellDrawLiftZ (#130).
-                        var physicsCellOrigin = envCell.Position.Origin + lbOffset;
-                        var cellOrigin = physicsCellOrigin + new System.Numerics.Vector3(
-                            0f, 0f, AcDream.App.Rendering.PortalVisibilityBuilder.ShellDrawLiftZ);
-                        var cellTransform =
-                            System.Numerics.Matrix4x4.CreateFromQuaternion(envCell.Position.Orientation) *
-                            System.Numerics.Matrix4x4.CreateTranslation(cellOrigin);
-                        var physicsCellTransform =
-                            System.Numerics.Matrix4x4.CreateFromQuaternion(envCell.Position.Orientation) *
-                            System.Numerics.Matrix4x4.CreateTranslation(physicsCellOrigin);
-
                         // Phase A8: register the cell with EnvCellRenderer for rendering.
                         // staticObjects is empty — cell stabs continue as separate WorldEntity
                         // records via the dispatcher (see lines below for the unchanged stab path).
@@ -5661,25 +5682,6 @@ public sealed class GameWindow : IDisposable
                             cellWorldPosition: cellOrigin,
                             cellRotation:      envCell.Position.Orientation,
                             staticObjects:     System.Array.Empty<(uint, System.Numerics.Vector3, System.Numerics.Quaternion, bool, System.Numerics.Matrix4x4)>());
-
-                        // Step 4: build LoadedCell for portal visibility — with the
-                        // PHYSICS (unlifted) transform. The +0.02 m render lift above
-                        // is a DRAW concern (shell z-fighting vs terrain); feeding it
-                        // into the visibility graph shifted every HORIZONTAL portal
-                        // plane 2 cm up, putting an eye standing on a deck/landing
-                        // 10–20 mm BELOW the lifted plane — outside the side test's
-                        // ±10 mm in-plane window — so the cell behind the portal was
-                        // side-culled: the tower-top staircase vanish + roof flap
-                        // (#119-residual; captured live at eye z=126.803 vs the
-                        // 010A→0107 plane at 126.80, reproduced ONLY with the lift in
-                        // TowerAscentReplayTests.CapturedTopOfStairs_*). Vertical
-                        // doorways were immune (the lift slides their planes along
-                        // themselves), which is why this hit exactly stairs, decks,
-                        // and cellar mouths.
-                        BuildLoadedCell(envCellId, envCell, cellStruct, physicsCellOrigin, physicsCellTransform);
-
-                        // Cache CellStruct physics BSP for indoor collision (UNCHANGED).
-                        _physicsDataCache.CacheCellStruct(envCellId, envCell, cellStruct, physicsCellTransform);
                     }
                 }
             }