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.

src/AcDream.Core/Physics/PhysicsObjUpdate.cs

@@ -45,6 +45,70 @@ public static class PhysicsObjUpdate
         body.calc_acceleration();
     }
 
+    /// <summary>
+    /// Commits the contact/walkable/collision-response tail of retail
+    /// <c>CPhysicsObj::SetPositionInternal</c> (<c>0x00515330</c>) in its
+    /// original order. The pre-transition flags are explicit because a
+    /// deferred placement may temporarily park the body without contact while
+    /// still needing the source edge when its destination cell becomes ready.
+    /// </summary>
+    /// <remarks>
+    /// Retail writes Contact and recalculates acceleration, calls
+    /// <c>set_on_walkable</c> (which invokes HitGround/LeaveGround), then calls
+    /// <c>handle_all_collisions</c> at <c>0x005154FE</c>. Collision response
+    /// must therefore observe any velocity change made by the movement
+    /// callback; moving that callback after reflection changes the result.
+    /// </remarks>
+    public static void CommitSetPositionTransition(
+        PhysicsBody body,
+        bool inContact,
+        bool onWalkable,
+        bool collisionNormalValid,
+        Vector3 collisionNormal,
+        bool previousContact,
+        bool previousOnWalkable,
+        Action? hitGround = null,
+        Action? leaveGround = null)
+    {
+        ArgumentNullException.ThrowIfNull(body);
+
+        // SetPositionInternal replaces Contact first but retains the source
+        // OnWalkable bit through its first calc_acceleration call. A deferred
+        // teleport may have parked the live body with both bits cleared, so
+        // restore the captured source bit explicitly before reproducing that
+        // ordering.
+        if (previousOnWalkable)
+            body.TransientState |= TransientStateFlags.OnWalkable;
+        else
+            body.TransientState &= ~TransientStateFlags.OnWalkable;
+
+        if (inContact)
+            body.TransientState |= TransientStateFlags.Contact;
+        else
+            body.TransientState &= ~TransientStateFlags.Contact;
+        body.calc_acceleration();
+
+        bool finalOnWalkable = inContact && onWalkable;
+        if (finalOnWalkable)
+            body.TransientState |= TransientStateFlags.OnWalkable;
+        else
+            body.TransientState &= ~TransientStateFlags.OnWalkable;
+
+        if (!previousOnWalkable && finalOnWalkable)
+            hitGround?.Invoke();
+        else if (previousOnWalkable && !finalOnWalkable)
+            leaveGround?.Invoke();
+        body.calc_acceleration();
+
+        HandleAllCollisions(
+            body,
+            collisionNormalValid,
+            collisionNormal,
+            previousContact,
+            previousOnWalkable,
+            finalOnWalkable);
+    }
+
     /// <summary>
     /// retail <c>handle_all_collisions</c> (0x00514780). Reflects or zeros the body's
     /// <see cref="PhysicsBody.Velocity"/> (retail m_velocityVector) based on