fix(health): evict deleted sites from the aggregator on the periodic site refresh

tests/ZB.MOM.WW.ScadaBridge.HealthMonitoring.Tests/CentralHealthAggregatorTests.cs

@@ -473,6 +473,27 @@ public class CentralHealthAggregatorTests
         Assert.False(aggregator.GetSiteState("site-a")!.IsMetricsStale);
     }
 
+    /// <summary>
+    /// Review 01 [Low]: <c>_siteStates</c> only ever grew — a site deleted from
+    /// configuration remained a permanently-offline dashboard tile (and a KPI
+    /// sample source) forever. Pruning against the known-site set evicts it; the
+    /// synthetic central id is always retained.
+    /// </summary>
+    [Fact]
+    public void PruneUnknownSites_RemovesDeletedSites_KeepsKnownAndCentral()
+    {
+        var (aggregator, _) = NewAggregator();
+        aggregator.ProcessReport(MakeReport("site-a", 1));
+        aggregator.ProcessReport(MakeReport("site-b", 1));
+        aggregator.ProcessReport(MakeReport(CentralHealthReportLoop.CentralSiteId, 1));
+
+        aggregator.PruneUnknownSites(new[] { "site-a" });
+
+        Assert.NotNull(aggregator.GetSiteState("site-a"));
+        Assert.Null(aggregator.GetSiteState("site-b"));
+        Assert.NotNull(aggregator.GetSiteState(CentralHealthReportLoop.CentralSiteId)); // synthetic id always kept
+    }
+
     /// <summary>
     /// Review 01 underdeveloped #7: "when did the site drop" was unanswerable.
     /// Every online↔offline flip stamps <see cref="SiteHealthState.LastStatusChangeAt"/>.

tests/ZB.MOM.WW.ScadaBridge.HealthMonitoring.Tests/CentralHealthReportLoopTests.cs

@@ -27,6 +27,7 @@ public class CentralHealthReportLoopTests
         public IReadOnlyDictionary<string, SiteHealthState> GetAllSiteStates() =>
             new Dictionary<string, SiteHealthState>();
         public SiteHealthState? GetSiteState(string siteId) => null;
+        public void PruneUnknownSites(IReadOnlyCollection<string> knownSiteIds) { }
     }
 
     /// <summary>
@@ -256,6 +257,7 @@ public class CentralHealthReportLoopTests
         public IReadOnlyDictionary<string, SiteHealthState> GetAllSiteStates() =>
             new Dictionary<string, SiteHealthState>();
         public SiteHealthState? GetSiteState(string siteId) => null;
+        public void PruneUnknownSites(IReadOnlyCollection<string> knownSiteIds) { }
     }
 
     [Fact]

tests/ZB.MOM.WW.ScadaBridge.HealthMonitoring.Tests/Kpi/SiteHealthKpiSampleSourceTests.cs

@@ -166,5 +166,8 @@ public class SiteHealthKpiSampleSourceTests
 
         public void MarkHeartbeat(string siteId, DateTimeOffset receivedAt) =>
             throw new NotSupportedException();
+
+        public void PruneUnknownSites(IReadOnlyCollection<string> knownSiteIds) =>
+            throw new NotSupportedException();
     }
 }