feat(vfx): port retail hidden and teleport presentation

Preserve canonical live-object ownership across Hidden transitions and remote teleport placement so effects, collision, streaming, and targeting remain synchronized.

tests/AcDream.Core.Tests/Physics/HandleAllCollisionsTests.cs

@@ -145,4 +145,62 @@ public class HandleAllCollisionsTests
         // dot = -5 < 0 → k = -(-5*1.05) = 5.25 → v.z = -5 + 5.25 = 0.25 (tiny bounce)
         Assert.Equal(0.25f, b.Velocity.Z, precision: 3);
     }
+
+    [Fact]
+    public void SetPositionTransition_HiddenLandingCallbackRunsBeforeCollisionResponse()
+    {
+        var body = Airborne(Vector3.Zero);
+        int hitGroundCalls = 0;
+
+        PhysicsObjUpdate.CommitSetPositionTransition(
+            body,
+            inContact: true,
+            onWalkable: true,
+            collisionNormalValid: true,
+            collisionNormal: Vector3.UnitZ,
+            previousContact: false,
+            previousOnWalkable: false,
+            hitGround: () =>
+            {
+                hitGroundCalls++;
+                body.Velocity = new Vector3(0f, 0f, -4f);
+            });
+
+        Assert.Equal(1, hitGroundCalls);
+        Assert.True(body.InContact);
+        Assert.True(body.OnWalkable);
+        // Callback -4 then retail elasticity 0.05 reflection => +0.2.
+        // Running the callback after collision response would leave -4.
+        Assert.Equal(0.2f, body.Velocity.Z, precision: 3);
+    }
+
+    [Fact]
+    public void SetPositionTransition_HiddenWalkOffCallbackRunsBeforeCollisionResponse()
+    {
+        var body = Airborne(Vector3.Zero);
+        body.TransientState = TransientStateFlags.Contact
+                            | TransientStateFlags.OnWalkable;
+        int leaveGroundCalls = 0;
+
+        PhysicsObjUpdate.CommitSetPositionTransition(
+            body,
+            inContact: false,
+            onWalkable: false,
+            collisionNormalValid: true,
+            collisionNormal: -Vector3.UnitX,
+            previousContact: true,
+            previousOnWalkable: true,
+            leaveGround: () =>
+            {
+                leaveGroundCalls++;
+                body.Velocity = new Vector3(3f, 0f, 0f);
+            });
+
+        Assert.Equal(1, leaveGroundCalls);
+        Assert.False(body.InContact);
+        Assert.False(body.OnWalkable);
+        // Callback +3 into a -X normal then reflection => -0.15.
+        // Running the callback after response would leave +3.
+        Assert.Equal(-0.15f, body.Velocity.X, precision: 3);
+    }
 }