refactor(runtime): unify generation reset for direct hosts

Move canonical per-session teardown into one retryable Runtime transaction, reduce App reset to projection acknowledgements, and prove the same GameRuntime graph through deterministic no-window lifecycle, gameplay, portal, fault, reconnect, and isolation gates.\n\nCo-authored-by: Codex <noreply@openai.com>

src/AcDream.Runtime/Entities/RuntimeEntityObjectLifetime.cs

@@ -968,15 +968,55 @@ public sealed class RuntimeEntityObjectLifetime : IDisposable
 
         _sessionClearInProgress = true;
         Entities.BeginSessionClear();
-        RuntimeEntityRecord[] retired = Entities.ActiveRecords.ToArray();
-        foreach (RuntimeEntityRecord canonical in retired)
+        RuntimeEntityRecord[] active = Entities.ActiveRecords.ToArray();
+        foreach (RuntimeEntityRecord canonical in active)
         {
             if (!Entities.RemoveActive(canonical))
                 continue;
             Entities.RetainTeardown(canonical);
             PublishEntity(RuntimeEntityChange.Deleted, canonical);
         }
-        return retired;
+        return active;
+    }
+
+    public IReadOnlyList<RuntimeEntityRecord>
+        CaptureSessionClearRetirements()
+    {
+        EnsureNotDisposed();
+        if (!_sessionClearInProgress)
+        {
+            throw new InvalidOperationException(
+                "Session-clear retirements are only available while the "
+                + "canonical clear transaction is active.");
+        }
+        return Entities.TeardownRecords.ToArray();
+    }
+
+    /// <summary>
+    /// Completes one exact incarnation retained by
+    /// <see cref="BeginSessionClear"/> after the borrowed host has retired its
+    /// presentation projection. Failure keeps the tombstone and local
+    /// identity intact so the same transaction cursor can retry this exact
+    /// record without reconstructing the retirement set.
+    /// </summary>
+    public void CompleteSessionEntityRetirement(
+        RuntimeEntityRecord canonical)
+    {
+        EnsureNotDisposed();
+        ArgumentNullException.ThrowIfNull(canonical);
+        if (!_sessionClearInProgress
+            || !Entities.TryGetTeardown(
+                canonical.ServerGuid,
+                canonical.Incarnation,
+                out RuntimeEntityRecord retained)
+            || !ReferenceEquals(retained, canonical))
+        {
+            throw new InvalidOperationException(
+                $"Live entity 0x{canonical.ServerGuid:X8}/{canonical.Incarnation} is not retained by the active session-clear transaction.");
+        }
+
+        CompleteProjectionRetirement(canonical);
+        Entities.ReleaseTeardown(canonical);
     }
 
     public bool CompleteSessionClearIfConverged()