refactor(app): extract focused window lifetime

Move the exact retryable shutdown manifest, typed root snapshot, terminal reporting, and native-window-last release out of GameWindow. Keep session and GPU convergence as hard barriers while reporting persistent physical callback cleanup without stranding dependent owners.

Co-authored-by: Codex <codex@openai.com>

src/AcDream.App/UI/UiHost.cs

@@ -152,7 +152,9 @@ public sealed class UiHost : System.IDisposable
     }
 
     /// <summary>Physically removes every retained input edge after quiescence.</summary>
-    public void DeactivateInput()
+    public void DeactivateInput() => CompleteInputShutdown(reportFailures: true);
+
+    private void CompleteInputShutdown(bool reportFailures)
     {
         QuiesceInput();
 
@@ -164,11 +166,21 @@ public sealed class UiHost : System.IDisposable
                     .Reverse()
                     .Select((binding, index) => new ResourceShutdownOperation(
                         $"input binding {index}",
-                        binding.Dispose))
+                        binding.Dispose,
+                        ResourceShutdownOperationPolicy.ReportAndContinue))
                     .ToArray()));
         _inputShutdown.CompleteOrThrow();
-        if (_inputShutdown.IsComplete)
+        if (_inputShutdown.IsComplete && _inputShutdown.CleanupFailures.Count == 0)
             _inputBindings.Clear();
+        if (reportFailures && _inputShutdown.CleanupFailures.Count != 0)
+        {
+            throw new AggregateException(
+                "Retained UI input callback cleanup completed with failures.",
+                _inputShutdown.CleanupFailures.Select(static failure =>
+                    new InvalidOperationException(
+                        $"Retained UI operation '{failure.Operation}' failed in stage '{failure.Stage}'.",
+                        failure.Error)));
+        }
     }
 
     // ── Window manager forwarders (delegate to UiRoot) ─────────────────
@@ -205,7 +217,7 @@ public sealed class UiHost : System.IDisposable
 
         _disposeRequested = true;
         _shutdown ??= CreateShutdownTransaction(
-            [DeactivateInput],
+            [() => CompleteInputShutdown(reportFailures: false)],
             () => { },
             WindowManager.Dispose,
             TextRenderer.Dispose);