feat(runtime): own initial create residence transaction

src/AcDream.Core/Physics/PhysicsTimestampGate.cs

@@ -102,6 +102,25 @@ public sealed class PhysicsTimestampGate
         return CreateObjectTimestampDisposition.ExistingGeneration;
     }
 
+    /// <summary>
+    /// Classifies an incoming CreateObject generation without consuming any
+    /// channel timestamp. Runtime uses this to preflight only admissions which
+    /// can create or replace a canonical incarnation; equal/stale packets must
+    /// still reach the normal per-channel retail gates unchanged.
+    /// </summary>
+    public CreateObjectTimestampDisposition PreviewCreateObject(
+        ushort instance)
+    {
+        if (!_seeded)
+            return CreateObjectTimestampDisposition.InitialGeneration;
+        ushort currentInstance = _timestamps[Instance];
+        if (IsNewer(currentInstance, instance))
+            return CreateObjectTimestampDisposition.NewGeneration;
+        if (IsNewer(instance, currentInstance))
+            return CreateObjectTimestampDisposition.StaleGeneration;
+        return CreateObjectTimestampDisposition.ExistingGeneration;
+    }
+
     public bool TryAcceptMovementEvent(
         ushort instance,
         ushort movement,