fix(ui): disposal guard on Alarm Summary live callback, matching the DebugView pattern (plan R2-07 T9)

src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Monitoring/AlarmSummary.razor

@@ -382,15 +382,20 @@
         _liveSubscription = null;
     }
 
+    // N7: set BEFORE teardown so a live callback racing Dispose is dropped both
+    // before the InvokeAsync marshal and inside it (mirrors DebugView.razor).
+    private volatile bool _disposed;
+
     // Raised on the aggregator's thread — marshal onto the circuit before touching state.
     private void OnLiveAlarmsChanged(int siteId)
     {
+        if (_disposed) return;
         _ = InvokeAsync(() =>
         {
             // Drop stale callbacks for a site we've since navigated away from, and
             // let the poll drive until the aggregator has actually seeded (so we never
             // clobber a good poll snapshot with an empty pre-seed list).
-            if (_selectedSiteId != siteId || !LiveAlarmCache.IsLive(siteId))
+            if (_disposed || _selectedSiteId != siteId || !LiveAlarmCache.IsLive(siteId))
             {
                 return;
             }
@@ -525,6 +530,7 @@
 
     public void Dispose()
     {
+        _disposed = true;
         StopTimer();
         DisposeLiveSubscription();
     }

tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Monitoring/AlarmSummaryRenderTests.cs

@@ -278,6 +278,30 @@ public class AlarmSummaryRenderTests : BunitContext
         });
     }
 
+    // ── arch-review R2 N7: disposal guard on the live callback ─────────────────
+
+    [Fact]
+    public void LiveCallbackRacingDispose_IsDropped_NoRebuildNoThrow()
+    {
+        var cut = RenderWithSiteSelected();
+        _liveCache.PushAlarms(new List<AlarmStateChanged>
+        {
+            new("Gamma", "G-alarm", AlarmState.Active, 300, DateTimeOffset.UtcNow),
+        });
+        cut.WaitForAssertion(() => Assert.Equal("Gamma", FirstRowInstance(cut)));
+
+        // Snapshot the callback BEFORE disposal — this models a delta thread that
+        // already read the delegate when Dispose ran (arch-review R2 N7).
+        var inFlight = _liveCache.CapturedCallback!;
+        cut.Instance.Dispose();
+
+        _liveCache.PushAlarms(new List<AlarmStateChanged>()); // mutate the fake's snapshot
+        var ex = Record.Exception(inFlight);
+        Assert.Null(ex);
+        // The disposed page must not have re-applied the (now empty) live snapshot.
+        Assert.Equal("Gamma", FirstRowInstance(cut));
+    }
+
     /// <summary>
     /// Controllable in-memory fake of <see cref="ISiteAlarmLiveCache"/>: records
     /// subscribe/dispose counts and lets a test push a live snapshot (which flips
@@ -293,6 +317,7 @@ public class AlarmSummaryRenderTests : BunitContext
         public int SubscribeCount { get; private set; }
         public int DisposeCount { get; private set; }
         public int? LastSubscribedSite { get; private set; }
+        public Action? CapturedCallback => _onChanged;
 
         public IDisposable Subscribe(int siteId, Action onChanged)
         {