diff --git a/src/AcDream.Core/Physics/TransitionTypes.cs b/src/AcDream.Core/Physics/TransitionTypes.cs
index 7364ec4..50dc718 100644
--- a/src/AcDream.Core/Physics/TransitionTypes.cs
+++ b/src/AcDream.Core/Physics/TransitionTypes.cs
@@ -1247,6 +1247,12 @@ public sealed class Transition
             this.SpherePath.WalkableAllowance = savedWalkableAllowance;
         }
 
+        // adjustedCenter (sphere slid onto polygon plane) is intentionally
+        // discarded — ValidateWalkable recomputes contact geometry from the
+        // world-space plane + foot position, consistent with the outdoor terrain
+        // path (SampleTerrainWalkable returns only plane + vertices, no adjusted
+        // sphere). The local is held only to satisfy the out param.
+
         if (!found || hitPoly is null) return false;
 
         // Transform hit polygon's plane + vertices to world space. Math is
diff --git a/tests/AcDream.Core.Tests/Physics/IndoorWalkablePlaneTests.cs b/tests/AcDream.Core.Tests/Physics/IndoorWalkablePlaneTests.cs
index 466c5d0..75f136e 100644
--- a/tests/AcDream.Core.Tests/Physics/IndoorWalkablePlaneTests.cs
+++ b/tests/AcDream.Core.Tests/Physics/IndoorWalkablePlaneTests.cs
@@ -167,6 +167,57 @@ public class IndoorWalkablePlaneTests
         Assert.False(found);
     }
 
+    [Fact]
+    public void TryFindIndoorWalkablePlane_WallPolyInBsp_ReturnsFalse()
+    {
+        // A polygon with a horizontal normal (Z = 0) is a wall, not a floor.
+        // walkable_hits_sphere rejects it: dp = dot(UnitZ, (0,1,0)) = 0 <= FloorZ.
+        // Regression coverage for the previous NoWalkablePolys_ReturnsFalse intent
+        // (the renamed NoBsp_ReturnsFalse only covers the null-BSP early-return).
+        Vector3[] wallVerts =
+        {
+            new Vector3(0f, 0f, 0f),
+            new Vector3(1f, 0f, 0f),
+            new Vector3(1f, 0f, 1f),
+            new Vector3(0f, 0f, 1f),
+        };
+        var resolved = new Dictionary<ushort, ResolvedPolygon>
+        {
+            [0] = new ResolvedPolygon
+            {
+                Vertices  = wallVerts,
+                Plane     = new Plane(new Vector3(0f, 1f, 0f), 0f),  // wall facing +Y
+                NumPoints = 4,
+                SidesType = CullMode.None,
+            },
+        };
+
+        var center = new Vector3(0.5f, 0f, 0.5f);
+        var bsp = BuildLeafBsp(new ushort[] { 0 }, center, 2f);
+
+        var cell = new CellPhysics
+        {
+            BSP                   = bsp,
+            WorldTransform        = Matrix4x4.Identity,
+            InverseWorldTransform = Matrix4x4.Identity,
+            Resolved              = resolved,
+        };
+
+        var transition = new Transition();
+        transition.SpherePath.WalkInterp = 1.0f;
+
+        // Foot sphere positioned to overlap the wall's plane (|Y - 0| = 0 < radius 0.48).
+        bool found = transition.TryFindIndoorWalkablePlane(
+            cell,
+            localFootCenter: new Vector3(0.5f, 0f, 0.5f),
+            sphereRadius: 0.48f,
+            out _,
+            out _,
+            out _);
+
+        Assert.False(found);
+    }
+
     [Fact]
     public void TryFindIndoorWalkablePlane_EmptyResolved_ReturnsFalse()
     {