diff --git a/src/AcDream.Core/Physics/TransitionTypes.cs b/src/AcDream.Core/Physics/TransitionTypes.cs
index 9749fdf..297edbf 100644
--- a/src/AcDream.Core/Physics/TransitionTypes.cs
+++ b/src/AcDream.Core/Physics/TransitionTypes.cs
@@ -2308,6 +2308,19 @@ public sealed class Transition
                 // the same 6-path dispatcher. For now we keep the swept-sphere
                 // cylinder test which matches the retail CylSphere behavior.
                 result = CylinderCollision(obj, sp);
+
+                // A6.P4 door investigation (2026-05-24): log every Cylinder
+                // shadow tested. Tells us whether the broadphase returned
+                // the door AND what CylinderCollision decided. Greppable
+                // alongside [entity-source] (which logs the door's radius
+                // / height at registration). Gated on ProbeBuildingEnabled.
+                if (PhysicsDiagnostics.ProbeBuildingEnabled)
+                {
+                    Vector3 dxy = obj.Position - sp.GlobalCurrCenter[0].Origin;
+                    float distXY = MathF.Sqrt(dxy.X * dxy.X + dxy.Y * dxy.Y);
+                    Console.WriteLine(System.FormattableString.Invariant(
+                        $"[cyl-test] obj=0x{obj.EntityId:X8} state=0x{obj.State:X8} radius={obj.Radius:F3} height={obj.CylHeight:F3} pos=({obj.Position.X:F2},{obj.Position.Y:F2},{obj.Position.Z:F2}) distXY={distXY:F3} result={result}"));
+                }
             }
 
             // L.2a slice 3: attribute the collision (if any) to this entity.