diff --git a/src/AcDream.App/Rendering/GameWindow.cs b/src/AcDream.App/Rendering/GameWindow.cs
index f68e8c3..d0be1cf 100644
--- a/src/AcDream.App/Rendering/GameWindow.cs
+++ b/src/AcDream.App/Rendering/GameWindow.cs
@@ -11176,20 +11176,31 @@ public sealed class GameWindow : IDisposable
             set: AcDream.App.Rendering.Wb.WbDrawDispatcher.EntitySet.OutdoorScenery);
         _a8PerfLastStaticStats = _wbDrawDispatcher.LastDrawStats;
 
-        // Step 5: per-other-building 3-bit stencil pipeline.
-        // WB VisibilityManager.cs:157-232
+        // Step 5: per-other-building 3-bit stencil pipeline (cross-building
+        // visibility — wire-in #3). WB VisibilityManager.cs:157-232.
         //
-        // GATED OFF BY DEFAULT. Current acdream does not yet have WB's
-        // portal-manager visibility/occlusion lifecycle; feeding this loop
-        // directly from all loaded building registries causes unrelated
-        // buildings' EnvCells to overwrite exterior walls through stale or
-        // over-broad portal masks. Keep the apparatus, but require an explicit
-        // opt-in until the portal list is proven equivalent to WB's
-        // _visibleBuildingPortals.
-        bool step5Enabled = string.Equals(
-            Environment.GetEnvironmentVariable("ACDREAM_A8_STEP5"), "1",
-            StringComparison.Ordinal);
-        if (step5Enabled && didInsideStencil && otherBuildings.Count > 0)
+        // Phase A8.F (Task 8, 2026-05-28): UNGATED. Previously gated behind
+        // ACDREAM_A8_STEP5 because bit 1 was the old flat all-exit-portals
+        // mask — feeding the cross-building pass from that over-broad mask let
+        // unrelated buildings' EnvCells overwrite exterior walls. That risk is
+        // gone now: bit 1 is the recursively-CLIPPED OutsideView written by
+        // MarkAndPunchNdc above (Task 6). Step 5a marks bit 2 only WHERE bit 1
+        // is set (StencilFunc Equal,3,0x01), so building B's cells render only
+        // where B's portals overlap our correctly-clipped opening (stencil==3 =
+        // bit1 AND bit2). In a cellar the stairwell-clipped OutsideView is tiny,
+        // so stencil==3 is essentially empty and Step 5 does ~nothing → no
+        // cellar artifacts. Non-overlapping buildings likewise produce empty
+        // stencil==3, so the frustum/radius-culled `otherBuildings` list is safe
+        // either way.
+        //
+        // The builder's CrossBuildingViews field is intentionally UNUSED:
+        // cross-building visibility is exit-portal screen-overlap, handled
+        // entirely by this loop reading the clipped bit 1. (CrossBuildingViews
+        // is dead output, slated for cleanup in a later task.)
+        //
+        // Runs whenever we're inside with a non-empty clipped OutsideView
+        // (didInsideStencil) and there is at least one other visible building.
+        if (didInsideStencil && otherBuildings.Count > 0)
         {
             gl.Enable(EnableCap.StencilTest);
             gl.ColorMask(false, false, false, false);
@@ -11262,9 +11273,10 @@ public sealed class GameWindow : IDisposable
             // anything that relies on alpha-to-coverage writing alpha). Restore
             // full ColorMask before returning to the outer render frame.
             //
-            // Step 5's iteration loop (when ACDREAM_A8_STEP5=1) leaves
-            // DepthMask=false / CullFace=disabled / ColorMask=(f,f,f,f) on
-            // its last iteration. Restore to acdream-default before returning.
+            // Step 5's iteration loop (now always-on when inside + other
+            // buildings overlap) leaves DepthMask=false / CullFace=disabled /
+            // ColorMask=(f,f,f,f) on its last iteration. Restore to
+            // acdream-default before returning.
             gl.ColorMask(true, true, true, true);
             gl.DepthMask(true);
             gl.DepthFunc(DepthFunction.Less);
@@ -11297,7 +11309,8 @@ public sealed class GameWindow : IDisposable
     //   - [envcells] cells>=1 tris>=1 filterCnt>=1 for at least one indoor frame
     //   - [stencil] op=mark verts>0 fires per camera-building
     //   - [draworder] shows steps 1 → 2 → 3 → 4 per indoor frame
-    //     (and 5{a,b,c,d} only when ACDREAM_A8_STEP5=1)
+    //     (and 5{a,b,c,d} whenever inside + a visible other building's
+    //      portals overlap the clipped bit-1 OutsideView)
 
     private int _phaseA8DrawOrderFrame = 0;