test(twincat): failing repro for STAB-16 silent replay failure

archreview/plans/R2-09-driver-fleet-batch-plan.md.tasks.json

@@ -186,7 +186,7 @@
     {
       "id": "B6.1",
       "subject": "B6: failing ReplayFailure_EmitsBadQuality_AndDegradesHealth in TwinCATReconnectReplayTests \u2014 STAB-16 repro",
-      "status": "pending",
+      "status": "completed",
       "blockedBy": []
     },
     {

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/TwinCATReconnectReplayTests.cs

@@ -170,6 +170,59 @@ public sealed class TwinCATReconnectReplayTests
         await drv.ShutdownAsync(TestContext.Current.CancellationToken);
     }
 
+    // ---- STAB-16 / STAB-17 / STAB-12 replay hardening ----
+
+    /// <summary>
+    ///     STAB-16: a replay failure must not be silent — the registration is marked dead, a Bad
+    ///     snapshot is pushed to subscribers (instead of the frozen-Good-stale value), and health
+    ///     degrades preserving the last successful read.
+    /// </summary>
+    [Fact]
+    public async Task ReplayFailure_EmitsBadQuality_AndDegradesHealth()
+    {
+        var build = 0;
+        var factory = new FakeTwinCATClientFactory
+        {
+            // client1 normal; client2 (the reconnect target) fails AddNotification (replay) + reads.
+            Customise = () => new FakeTwinCATClient
+            {
+                ThrowOnAddNotification = ++build >= 2,
+                ThrowOnRead = build >= 2,
+                Exception = new InvalidOperationException("ADS notification quota exceeded"),
+            },
+        };
+        var drv = new TwinCATDriver(new TwinCATDriverOptions
+        {
+            Devices = [new TwinCATDeviceOptions(Host)],
+            Tags = [new TwinCATTagDefinition("Speed", Host, "MAIN.Speed", TwinCATDataType.DInt)],
+            Probe = new TwinCATProbeOptions { Enabled = false },
+            UseNativeNotifications = true,
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", TestContext.Current.CancellationToken);
+
+        var events = new ConcurrentQueue<DataChangeEventArgs>();
+        drv.OnDataChange += (_, e) => events.Enqueue(e);
+
+        _ = await drv.SubscribeAsync(["Speed"], TimeSpan.FromMilliseconds(250), TestContext.Current.CancellationToken);
+        // Establish a last-successful-read on the healthy client1.
+        _ = await drv.ReadAsync(["Speed"], TestContext.Current.CancellationToken);
+        var lastGoodRead = drv.GetHealth().LastSuccessfulRead;
+        lastGoodRead.ShouldNotBeNull();
+
+        // Drop the wire; the next read reconnects onto client2, whose replay AddNotification fails.
+        factory.Clients[0].SimulateWireDrop();
+        _ = await drv.ReadAsync(["Speed"], TestContext.Current.CancellationToken);
+
+        // STAB-16: subscribers see the tag go Bad (not frozen Good), and health degraded while
+        // preserving the last successful read.
+        var bad = events.SingleOrDefault(e => e.FullReference == "Speed"
+                                              && e.Snapshot.StatusCode == TwinCATStatusMapper.BadCommunicationError);
+        bad.ShouldNotBeNull("a failed replay must publish a Bad snapshot for the affected reference");
+        var health = drv.GetHealth();
+        health.State.ShouldBe(DriverState.Degraded);
+        health.LastSuccessfulRead.ShouldBe(lastGoodRead);
+    }
+
     private static async Task WaitForAsync(Func<bool> condition, TimeSpan timeout)
     {
         var deadline = DateTime.UtcNow + timeout;