feat(app): project canonical runtime placements

src/AcDream.Runtime/World/RuntimeWorldTransitState.cs

@@ -1,4 +1,5 @@
 using System.Globalization;
+using AcDream.Runtime.Physics;
 
 namespace AcDream.Runtime.World;
 
@@ -247,6 +248,32 @@ public sealed class RuntimeWorldTransitState
         return false;
     }
 
+    /// <summary>
+    /// Validates the portal suffix carried by a canonical SetPosition
+    /// projection receipt against this instance's live transit ownership.
+    /// Shape equality alone is insufficient: a superseded, cancelled, or
+    /// completed host token can remain structurally valid after it has lost
+    /// authority to reveal the destination.
+    /// </summary>
+    public bool IsCurrentPlacementAuthority(
+        in RuntimePortalPlacementAuthority authority,
+        uint exactCellId)
+    {
+        if (!authority.Present)
+            return authority.IsEmpty;
+
+        return authority.IsValid
+            && authority.Projection.DestinationCell == exactCellId
+            && IsCurrentPortalDestination(
+                authority.RevealGeneration,
+                authority.TeleportSequence,
+                exactCellId)
+            && TryGetHostProjection(
+                authority.Projection,
+                out RuntimeWorldHostProjectionSnapshot host)
+            && !host.IsSuperseding;
+    }
+
     /// <summary>
     /// Marks the graphical reservation-release callback as due before the
     /// host executes it. A thrown callback therefore leaves an exact pending