diff --git a/src/AcDream.Core/Physics/PhysicsEngine.cs b/src/AcDream.Core/Physics/PhysicsEngine.cs
index 4f2b8dd..f36b704 100644
--- a/src/AcDream.Core/Physics/PhysicsEngine.cs
+++ b/src/AcDream.Core/Physics/PhysicsEngine.cs
@@ -128,24 +128,21 @@ public sealed class PhysicsEngine
             targetZ = terrainZ;
             targetCellId = physics.Terrain.ComputeOutdoorCellId(localCandX, localCandY);
         }
-        else if (!currentlyIndoor && bestCellZ is not null
-                 && MathF.Abs(bestCellZ.Value - currentPos.Z) < stepUpHeight + 2f
-                 && bestCellZ.Value < terrainZ - 1f)
+#pragma warning disable CS0162
+        else if (false)  // Phase B.2 MVP: outdoor→indoor transition DISABLED.
         {
-            // Walked into an indoor cell from outdoor — transition to indoor.
-            // The extra guard `bestCellZ < terrainZ - 1` prevents transitioning
-            // into cells whose floor is AT or ABOVE terrain level — those are
-            // typically roofs, upper floors, or building footprints that overlap
-            // the outdoor terrain. A genuine indoor transition is into a cell
-            // whose floor is BELOW the terrain surface (basements, ground floors
-            // of buildings that sit on elevated terrain). Without this guard,
-            // standing near any building with a floor polygon covering the
-            // player's XY triggers an indoor transition and snaps Z to the
-            // cell's floor — which for multi-story buildings can be 30+ units
-            // below the outdoor terrain.
-            targetZ = bestCellZ.Value;
+            // The CellSurface floor polygons are too aggressive — building
+            // footprints, roofs, and upper floors all have physics polygons
+            // that cover wide XY areas at various Z levels. Any outdoor
+            // position near a building matches a cell floor, and the engine
+            // snaps into it regardless of how far below the terrain the
+            // floor actually is. Proper indoor transition requires portal
+            // detection (CellPortal boundary crossing), not floor-polygon
+            // containment. Disabled until Phase E implements that.
+            targetZ = bestCellZ!.Value;
             targetCellId = bestCell!.CellId & 0xFFFFu;
         }
+#pragma warning restore CS0162
         else
         {
             // Stay outdoors on terrain.