perf(ui): shared KPI cache, live-cache-backed alarm summary, coalesced debug renders

src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/Deployments.razor

@@ -236,13 +236,66 @@
         DeploymentStatusNotifier.StatusChanged += OnDeploymentStatusChanged;
     }
 
+    // ── Push coalescing (arch-review WP2.4) ───────────────────────────────────
+    // One reload = every deployment record + every instance, re-read and re-filtered.
+    // The notifier fires per status WRITE, so a site deploy of N instances produced
+    // 2N+ of those full reloads back to back, per circuit. The reload is now
+    // leading-edge debounced: the first push after an idle gap still reloads
+    // immediately (a single deployment stays as responsive as before), and every
+    // push inside the window is absorbed into ONE trailing reload.
+    private const int ReloadDebounceMs = 500;
+
+    private DateTimeOffset _lastReloadAt = DateTimeOffset.MinValue;
+
+    /// <summary>Coalescing timer for pushes arriving inside the debounce window. Disposed with the component.</summary>
+    private Timer? _coalesceTimer;
+
     private void OnDeploymentStatusChanged(ZB.MOM.WW.ScadaBridge.DeploymentManager.DeploymentStatusChange change)
     {
         // CentralUI-022: a callback racing disposal must not touch the component.
         if (_disposed || !_autoRefresh) return;
+
+        lock (_coalesceLock)
+        {
+            if (_disposed) return;
+
+            var sinceLast = DateTimeOffset.UtcNow - _lastReloadAt;
+            if (sinceLast >= TimeSpan.FromMilliseconds(ReloadDebounceMs))
+            {
+                // Idle — reload straight away (leading edge).
+                _lastReloadAt = DateTimeOffset.UtcNow;
+            }
+            else
+            {
+                // Inside the window: arm one trailing reload for the remainder, and
+                // let any further push in this window ride it.
+                if (_coalesceTimer is not null) return;
+
+                var delay = TimeSpan.FromMilliseconds(ReloadDebounceMs) - sinceLast;
+                _coalesceTimer = new Timer(_ => OnCoalesceElapsed(), null, delay, Timeout.InfiniteTimeSpan);
+                return;
+            }
+        }
+
         _ = DispatchReloadAsync();
     }
 
+    /// <summary>Trailing edge of the debounce: disarm, stamp, and run the one coalesced reload.</summary>
+    private void OnCoalesceElapsed()
+    {
+        lock (_coalesceLock)
+        {
+            _coalesceTimer?.Dispose();
+            _coalesceTimer = null;
+            if (_disposed) return;
+            _lastReloadAt = DateTimeOffset.UtcNow;
+        }
+
+        _ = DispatchReloadAsync();
+    }
+
+    private readonly object _coalesceLock = new();
+
     /// <summary>
     /// Reloads the deployment table on the renderer's dispatcher, guarded
     /// against the component being disposed mid-flight (CentralUI-022):
@@ -361,5 +414,10 @@
         // status change reaches this disposed component.
         _disposed = true;
         DeploymentStatusNotifier.StatusChanged -= OnDeploymentStatusChanged;
+        lock (_coalesceLock)
+        {
+            _coalesceTimer?.Dispose();
+            _coalesceTimer = null;
+        }
     }
 }