diff --git a/src/AcDream.App/Rendering/GameWindow.cs b/src/AcDream.App/Rendering/GameWindow.cs
index 4df8455..d75cd66 100644
--- a/src/AcDream.App/Rendering/GameWindow.cs
+++ b/src/AcDream.App/Rendering/GameWindow.cs
@@ -7279,8 +7279,21 @@ public sealed class GameWindow : IDisposable
             // Phase N.5b: wrap Draw in CPU stopwatch for [TERRAIN-DIAG] rollup
             // (gated on ACDREAM_WB_DIAG=1, same env var as [WB-DIAG]). Stopwatch
             // is cheap; only the periodic Console.WriteLine is gated.
+            //
+            // FIX 2026-05-28: skip this terrain pass when cameraInsideBuilding.
+            // RenderInsideOutAcdream's Step 4 draws terrain stencil-gated to
+            // portal silhouettes (matching WB VisibilityManager:143). Drawing
+            // terrain BOTH here (full-screen) AND in Step 4 (stencil-gated)
+            // doubles GPU work AND causes Z-fighting at cottage walls — the
+            // lower wall portion (Z=92-94) overlaps terrain Z=92, terrain's
+            // depth from this pass is already in the depth buffer when Step
+            // 3 writes the cell mesh. The pre-A8 code papered over this with
+            // a depth-clear-if-inside workaround which we deleted in Wave 4.
+            // The proper fix is to NOT draw terrain here when indoor; Step 4
+            // is the single, stencil-gated terrain pass.
             _terrainCpuStopwatch.Restart();
-            _terrain?.Draw(camera, frustum, neverCullLandblockId: playerLb);
+            if (!cameraInsideBuilding)
+                _terrain?.Draw(camera, frustum, neverCullLandblockId: playerLb);
             _terrainCpuStopwatch.Stop();
             // Multiply by 100 then divide by 100 in the diag print to keep
             // 0.01 µs precision in the long-typed sample buffer. Terrain Draw