fix(health-monitoring): resolve HealthMonitoring-004,006,010,011,012 — heartbeat-doc accuracy, testable sequence seeding, logged failures, dead-code removal

tests/ScadaLink.HealthMonitoring.Tests/CentralHealthReportLoopTests.cs

@@ -110,6 +110,29 @@ public class CentralHealthReportLoopTests
         }
     }
 
+    /// <summary>
+    /// HealthMonitoring-006 regression: the central loop's sequence-number seed
+    /// must be derived from the injected <see cref="TimeProvider"/> (Unix-ms),
+    /// not from <c>DateTimeOffset.UtcNow</c> read at field initialization, so the
+    /// seeding strategy is deterministically testable.
+    /// </summary>
+    [Fact]
+    public void SequenceNumberSeed_UsesInjectedTimeProvider()
+    {
+        var fixedInstant = new DateTimeOffset(2026, 5, 16, 12, 0, 0, TimeSpan.Zero);
+        var timeProvider = new TestTimeProvider(fixedInstant);
+
+        var loop = new CentralHealthReportLoop(
+            new SiteHealthCollector(),
+            new RecordingAggregator(),
+            new FakeClusterNodeProvider { SelfIsPrimary = true },
+            Options.Create(new HealthMonitoringOptions()),
+            NullLogger<CentralHealthReportLoop>.Instance,
+            timeProvider);
+
+        Assert.Equal(fixedInstant.ToUnixTimeMilliseconds(), loop.CurrentSequenceNumber);
+    }
+
     [Fact]
     public async Task SetsActiveNodeFlag_EvenWhenNotPrimary()
     {