diff --git a/src/AcDream.App/Rendering/GameWindow.cs b/src/AcDream.App/Rendering/GameWindow.cs
index 1bfce28..6227452 100644
--- a/src/AcDream.App/Rendering/GameWindow.cs
+++ b/src/AcDream.App/Rendering/GameWindow.cs
@@ -3090,41 +3090,60 @@ public sealed class GameWindow : IDisposable
             return;
 
         float entScale = spawn.ObjScale ?? 1.0f;
-        float radius;
-        float height;
 
-        if (hasCyl)
+        // A6.P4 door fix (2026-05-24): build the multi-part shape list.
+        // ShadowShapeBuilder emits one entry per CylSphere, one per Sphere
+        // (only when no CylSpheres), and one per Part with a non-null
+        // PhysicsBSP. Retail-faithful per CTransition::find_obj_collisions
+        // → CPartArray::FindObjCollisions
+        // (acclient_2013_pseudo_c.txt:286236). Pre-fix doors registered
+        // ONE small Cylinder via setup.Radius / Sphere — too narrow to
+        // span the doorway gap, so the player could walk through. With
+        // this change the door also registers the part-0 BSP slab
+        // (1.9 × 0.26 × 2.5 m) that retail uses for the real block.
+        var raw = AcDream.Core.Physics.ShadowShapeBuilder.FromSetup(
+            setup, entScale,
+            id => _physicsDataCache.GetGfxObj(id)?.BSP?.Root is not null);
+
+        // Substitute the real bounding-sphere radius for BSP shapes —
+        // the pure builder's 2.0 placeholder works for typical doors
+        // (BS radius ≈ 1.975 m) but is loose for larger entities and
+        // tight for smaller ones. Mirrors the landblock-static path's
+        // pattern of pulling the real radius from PhysicsDataCache.
+        var shapes = new List<AcDream.Core.Physics.ShadowShape>(raw.Count);
+        foreach (var s in raw)
         {
-            // Pick the largest CylSphere as the body cylinder. Retail
-            // tests every CylSphere in turn (276891) but for collision
-            // BLOCKING the largest is sufficient — the player will stop
-            // at the body's outer radius.
-            var sph = setup.CylSpheres[0];
-            for (int i = 1; i < setup.CylSpheres.Count; i++)
+            if (s.CollisionType == AcDream.Core.Physics.ShadowCollisionType.BSP)
             {
-                if (setup.CylSpheres[i].Radius > sph.Radius) sph = setup.CylSpheres[i];
+                var phys = _physicsDataCache.GetGfxObj(s.GfxObjId);
+                float bspR = (phys?.BoundingSphere?.Radius ?? 2f) * entScale;
+                shapes.Add(s with { Radius = bspR });
             }
-            radius = sph.Radius * entScale;
-            height = (sph.Height > 0 ? sph.Height : sph.Radius * 4f) * entScale;
-        }
-        else if (hasRadius)
-        {
-            radius = setup.Radius * entScale;
-            height = (setup.Height > 0 ? setup.Height : setup.Radius * 2f) * entScale;
-        }
-        else
-        {
-            // Sphere-only: largest sphere as a Cylinder approximation.
-            var sph = setup.Spheres[0];
-            for (int i = 1; i < setup.Spheres.Count; i++)
+            else
             {
-                if (setup.Spheres[i].Radius > sph.Radius) sph = setup.Spheres[i];
+                shapes.Add(s);
             }
-            radius = sph.Radius * entScale;
-            height = sph.Radius * 2f * entScale;
         }
 
-        if (radius <= 0f) return;
+        // setup.Radius fallback: the builder doesn't emit a Radius-only
+        // shape (it only walks CylSpheres / Spheres / Parts). For entities
+        // with no CylSpheres / Spheres / BSP-bearing Parts but a non-zero
+        // Radius (rare — simple decorative props), preserve the prior
+        // behavior of registering a setup.Radius cylinder so we don't
+        // silently regress those entities' collision.
+        if (shapes.Count == 0 && hasRadius)
+        {
+            shapes.Add(new AcDream.Core.Physics.ShadowShape(
+                GfxObjId:      0u,
+                LocalPosition: System.Numerics.Vector3.Zero,
+                LocalRotation: System.Numerics.Quaternion.Identity,
+                Scale:         entScale,
+                CollisionType: AcDream.Core.Physics.ShadowCollisionType.Cylinder,
+                Radius:        setup.Radius * entScale,
+                CylHeight:     (setup.Height > 0 ? setup.Height : setup.Radius * 2f) * entScale));
+        }
+
+        if (shapes.Count == 0) return;
 
         // Decode PvP / Player / Impenetrable from PWD._bitfield.
         // IsCreature comes from the spawn's ItemType (server-known type).
@@ -3136,17 +3155,31 @@ public sealed class GameWindow : IDisposable
 
         uint state = spawn.PhysicsState ?? 0u;
 
-        _physicsEngine.ShadowObjects.Register(
-            entity.Id, entity.SourceGfxObjOrSetupId,
-            entity.Position, entity.Rotation, radius,
-            origin.X, origin.Y, spawn.Position.Value.LandblockId,
-            AcDream.Core.Physics.ShadowCollisionType.Cylinder,
-            cylHeight: height, scale: 1.0f,
-            state: state, flags: flags);
+        _physicsEngine.ShadowObjects.RegisterMultiPart(
+            entityId:        entity.Id,
+            entityWorldPos:  entity.Position,
+            entityWorldRot:  entity.Rotation,
+            shapes:          shapes,
+            state:           state,
+            flags:           flags,
+            worldOffsetX:    origin.X,
+            worldOffsetY:    origin.Y,
+            landblockId:     spawn.Position.Value.LandblockId);
+
         // L.2d slice 1 (2026-05-13): [entity-source] greppable from [resolve-bldg].
+        // Per-shape detail appears in [resolve-bldg] when collisions fire;
+        // this entity-level line keeps the spawn-time identification.
         if (AcDream.Core.Physics.PhysicsDiagnostics.ProbeBuildingEnabled)
+        {
+            int nCyl = 0, nBsp = 0;
+            foreach (var s in shapes)
+            {
+                if (s.CollisionType == AcDream.Core.Physics.ShadowCollisionType.Cylinder) nCyl++;
+                else nBsp++;
+            }
             Console.WriteLine(System.FormattableString.Invariant(
-                $"[entity-source] id=0x{entity.Id:X8} entityId=0x{entity.Id:X8} src=0x{entity.SourceGfxObjOrSetupId:X8} gfxObj=0x{entity.SourceGfxObjOrSetupId:X8} lb=0x{spawn.Position.Value.LandblockId:X8} type=Cylinder note=server-spawn-root state=0x{state:X8} flags={flags}"));
+                $"[entity-source] id=0x{entity.Id:X8} entityId=0x{entity.Id:X8} src=0x{entity.SourceGfxObjOrSetupId:X8} gfxObj=0x{entity.SourceGfxObjOrSetupId:X8} lb=0x{spawn.Position.Value.LandblockId:X8} shapes=cyl{nCyl}+bsp{nBsp} note=server-spawn-root state=0x{state:X8} flags={flags}"));
+        }
     }
 
     private bool RemoveLiveEntityByServerGuid(uint serverGuid, bool logDelete)