fix(render): outdoor look-in draws interior cells only through real doorway apertures (no see-through walls)

Cutover-flip follow-up: see-through buildings from outside. When the outdoor-node flood reaches a building, each interior cell is meant to draw clipped to its doorway aperture. But DrawEnvCellShells falls back to the no-clip slot 0 (full-screen) when a cell's aperture degenerates — screen-covering when you get close, or edge-on. Indoors that fallback is load-bearing (it seals the room the camera stands in; near walls hide the over-draw). From OUTSIDE it paints the building interior across the whole screen, depth-tested, so it shows wherever the solid exterior does not cover — the see-through walls, appearing 'past a threshold' exactly where the aperture degenerates.

Fix: for the outdoor-node root only, skip a flooded interior cell with no real plane-clip slot (HasRealClipSlot). From outside, 'no real aperture' means 'do not paint this interior', not 'paint it everywhere'. Interior roots keep the seal-everything slot-0 fallback unchanged. Applied to DrawEnvCellShells AND DrawCellObjectLists so a skipped cell shows neither walls nor furniture; the dead DrawPortal exterior look-in gets the same gate.

Root cause traced over the WB EnvCell render path: CellMesh.cs is physics-only; ObjectMeshManager.PrepareCellStructMeshData builds double-sided walls, so this was never a culling bug. App 216/0, build green. Visual gate pending.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/AcDream.App/Rendering/RetailPViewRenderer.cs

@@ -76,11 +76,18 @@ public sealed class RetailPViewRenderer
 
         ctx.EmitDiagnostics?.Invoke(result);
 
+        // Render unification: from the OUTDOOR-node root a flooded interior cell must draw ONLY within
+        // its real doorway aperture (a plane-clip slot). A cell whose aperture degenerates to the
+        // no-clip slot 0 (screen-covering / edge-on) would otherwise draw FULL-SCREEN and paint the
+        // building interior across the whole screen — the see-through-walls bug. Indoor roots keep the
+        // seal-everything slot-0 fallback (load-bearing: it seals the room the camera stands in).
+        bool outdoorRoot = ctx.RootCell.IsOutdoorNode;
+
         DrawLandscapeThroughOutsideView(ctx, clipAssembly, partition);
         UseIndoorMembershipOnlyRouting();
         DrawExitPortalMasks(ctx, pvFrame, clipAssembly, drawableCells);
-        DrawEnvCellShells(ctx, pvFrame, clipAssembly, drawableCells);
+        DrawEnvCellShells(ctx, pvFrame, clipAssembly, drawableCells, outdoorRoot);
-        DrawCellObjectLists(ctx, pvFrame, clipAssembly, drawableCells, partition);
+        DrawCellObjectLists(ctx, pvFrame, clipAssembly, drawableCells, partition, outdoorRoot);
 
         return result;
     }
@@ -128,8 +135,11 @@ public sealed class RetailPViewRenderer
         ctx.EmitDiagnostics?.Invoke(result);
 
         DrawExitPortalMasks(ctx, pvFrame, clipAssembly, drawableCells);
-        DrawEnvCellShells(ctx, pvFrame, clipAssembly, drawableCells);
+        // DrawPortal is the exterior look-in (camera outside, peering in) → same outdoor gate: an
-        DrawCellObjectLists(ctx, pvFrame, clipAssembly, drawableCells, partition);
+        // interior cell with no real doorway aperture must not draw full-screen. (This path is dead
+        // after the cutover flip; kept compiling until the Step-D deletion.)
+        DrawEnvCellShells(ctx, pvFrame, clipAssembly, drawableCells, outdoorRoot: true);
+        DrawCellObjectLists(ctx, pvFrame, clipAssembly, drawableCells, partition, outdoorRoot: true);
         RestoreNoClip(ctx.SetTerrainClipUbo);
 
         return result;
@@ -181,15 +191,19 @@ public sealed class RetailPViewRenderer
         IRetailPViewCellDrawCallbacks ctx,
         PortalVisibilityFrame pvFrame,
         ClipFrameAssembly clipAssembly,
-        HashSet<uint> drawableCells) // param kept this task; removed in Task 4
+        HashSet<uint> drawableCells, // param kept this task; removed in Task 4
+        bool outdoorRoot)
     {
         // Retail DrawCells Loop 2: every visible cell's shell, reverse cell_draw_list
-        // (far→near), per portal_view slice. No drawableCells filter — a cell without a
+        // (far→near), per portal_view slice. Indoors a cell without a clip-slot falls through
-        // clip-slot falls through GetCellSlicesOrNoClip to NoClipSlice and draws unclipped
+        // GetCellSlicesOrNoClip to NoClipSlice and draws unclipped (sealed — load-bearing R1 seal).
-        // (sealed; per-slice trim returns in Task 4).
+        // Outdoors (outdoor-node root) that same unclipped draw IS the see-through bug, so a cell with
+        // no real plane-clip aperture is skipped entirely (see DrawInside).
         foreach (var entry in IndoorDrawPlan.ShellPass(pvFrame))
         {
             uint cellId = entry.CellId;
+            if (outdoorRoot && !HasRealClipSlot(clipAssembly, cellId))
+                continue;
             _oneCell.Clear();
             _oneCell.Add(cellId);
 
@@ -207,7 +221,8 @@ public sealed class RetailPViewRenderer
         PortalVisibilityFrame pvFrame,
         ClipFrameAssembly clipAssembly,
         HashSet<uint> drawableCells,
-        InteriorEntityPartition.Result partition)
+        InteriorEntityPartition.Result partition,
+        bool outdoorRoot)
     {
         for (int i = pvFrame.OrderedVisibleCells.Count - 1; i >= 0; i--)
         {
@@ -215,6 +230,11 @@ public sealed class RetailPViewRenderer
             if (!drawableCells.Contains(cellId))
                 continue;
 
+            // Outdoor-node root: skip a cell with no real doorway aperture (would draw full-screen) —
+            // matches DrawEnvCellShells so a skipped interior cell shows neither walls nor furniture.
+            if (outdoorRoot && !HasRealClipSlot(clipAssembly, cellId))
+                continue;
+
             if (!partition.ByCell.TryGetValue(cellId, out var bucket) || bucket.Count == 0)
                 continue;
 
@@ -240,6 +260,24 @@ public sealed class RetailPViewRenderer
         return new[] { NoClipSlice };
     }
 
+    /// <summary>
+    /// True iff <paramref name="cellId"/> has at least one view slice backed by a real plane-clip
+    /// slot (slot != 0) in this frame's assembly — i.e. a genuine doorway aperture. A cell with no
+    /// entry, or only the no-clip slot 0 (screen-covering / degenerate aperture → scissor fallback),
+    /// returns false. Used by the outdoor-node root to refuse drawing an interior cell that would
+    /// otherwise paint full-screen (the see-through-walls bug). Slot 0 is reserved as no-clip
+    /// (<see cref="NoClipSlice"/>), so "real aperture" is precisely "some slot != 0".
+    /// </summary>
+    private static bool HasRealClipSlot(ClipFrameAssembly clipAssembly, uint cellId)
+    {
+        if (!clipAssembly.CellIdToViewSlices.TryGetValue(cellId, out var slices))
+            return false;
+        foreach (var slice in slices)
+            if (slice.Slot != 0)
+                return true;
+        return false;
+    }
+
     private void UseIndoorMembershipOnlyRouting()
     {
         // Retail's PView portal views decide which cells/objects are eligible,