fix(abcip,focas): collapse alarm projection to a single poll loop (no reconnect leak)

The owning DriverInstanceActor re-subscribes alarms on every Connected
entry (DetachAlarmSource nulls its cached handle on Connected->Reconnecting
without calling UnsubscribeAlarmsAsync), and the driver object + its alarm
projection are reused across every in-place reconnect. Each SubscribeAsync
started a fresh, never-cancelled Task.Run poll loop and added it to _subs,
so N reconnects leaked N concurrent loops all polling the device and all
firing the same raise/clear transitions => duplicate alarm events + CPU/mem
growth.

Mirrors the Galaxy #399 fix (Clear-before-Add) but for live poll loops the
collapse must also CANCEL the superseded loops, not just drop references.
SubscribeAsync now snapshots existing subs under _subsLock, clears _subs,
adds the new sub, starts its loop, then retires each stale sub out-of-band
(RetireAsync: Cancel + await loop + Dispose CTS, fire-and-forget so the new
subscription's return isn't blocked on a poll interval). Snapshot+clear under
the same lock DisposeAsync uses guarantees no double-own / double-dispose.

There is exactly one consumer per driver instance (factory-per-actor), so
retiring all prior subscriptions before starting the new one is faithful.

Regression tests (TDD, fail->pass): subscribe twice then drive one device
raise; assert OnAlarmEvent fires exactly once (was twice with two leaked
loops).

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/AbCipAlarmProjectionTests.cs

@@ -119,6 +119,68 @@ public sealed class AbCipAlarmProjectionTests
         await drv.ShutdownAsync(CancellationToken.None);
     }
 
+    /// <summary>
+    ///     Regression for the reconnect poll-loop leak (#399 sibling): the owning
+    ///     DriverInstanceActor re-subscribes alarms on every Connected entry without first calling
+    ///     Unsubscribe, and the driver object (and its projection) survives the in-place reconnect.
+    ///     Each SubscribeAsync used to start a fresh, never-cancelled poll loop — so after N
+    ///     reconnects there were N live loops all polling the device and all firing the same
+    ///     raise/clear transition, producing DUPLICATE alarm events.
+    ///
+    ///     This simulates two re-subscribes (one reconnect) against the same source, then drives
+    ///     ONE 0->1 device transition. After the collapse-to-single-loop fix exactly one loop is
+    ///     alive so the raise fires exactly once; before the fix both loops fire it ⇒ two events.
+    /// </summary>
+    [Fact]
+    public async Task Resubscribe_Collapses_To_Single_Loop_No_Duplicate_Raise()
+    {
+        var factory = new FakeAbCipTagFactory();
+        var opts = new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions(Device)],
+            Tags = [AlmdTag("HighTemp")],
+            EnableAlarmProjection = true,
+            AlarmPollInterval = TimeSpan.FromMilliseconds(20),
+            EnableDeclarationOnlyUdtGrouping = true,
+        };
+        var drv = new AbCipDriver(opts, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var raises = new List<AlarmEventArgs>();
+        drv.OnAlarmEvent += (_, e) =>
+        {
+            if (e.Message.Contains("raised")) lock (raises) raises.Add(e);
+        };
+
+        // First subscribe creates + starts polling the HighTemp runtime. Seed InFaulted=false +
+        // a severity so the loop's baseline settles on "not faulted".
+        var sub1 = await drv.SubscribeAlarmsAsync(["HighTemp"], CancellationToken.None);
+        await WaitForTagCreation(factory, "HighTemp");
+        factory.Tags["HighTemp"].ValuesByOffset[0] = 0;   // InFaulted=false at offset 0
+        factory.Tags["HighTemp"].ValuesByOffset[8] = 500; // Severity at offset 8
+        await Task.Delay(80); // let sub1's loop seed its "last-seen false" baseline
+
+        // Second subscribe = the actor re-subscribing across a reconnect. Its loop reads the same
+        // shared HighTemp runtime; give it time to seed its own "last-seen false" baseline too.
+        var sub2 = await drv.SubscribeAlarmsAsync(["HighTemp"], CancellationToken.None);
+        await Task.Delay(80);
+
+        factory.Tags["HighTemp"].ValuesByOffset[0] = 1; // one 0->1 transition
+        // Wait past several 20ms poll intervals so any leaked second loop has ample time to also
+        // fire its duplicate raise before we assert.
+        await Task.Delay(250);
+
+        await drv.UnsubscribeAlarmsAsync(sub1, CancellationToken.None);
+        await drv.UnsubscribeAlarmsAsync(sub2, CancellationToken.None);
+        await drv.ShutdownAsync(CancellationToken.None);
+
+        lock (raises)
+        {
+            raises.Count.ShouldBe(1,
+                "exactly one poll loop must survive a re-subscribe; a leaked loop fires a duplicate raise");
+        }
+    }
+
     /// <summary>Verifies that alarm clear event fires on 1-to-0 transition.</summary>
     [Fact]
     public async Task Clear_Event_Fires_On_1_to_0_Transition()

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasAlarmProjectionTests.cs

@@ -69,6 +69,64 @@ public sealed class FocasAlarmProjectionTests
         events[0].SourceNodeId.ShouldBe(Host);
     }
 
+    /// <summary>
+    ///     Regression for the reconnect poll-loop leak (#399 sibling): the owning
+    ///     DriverInstanceActor re-subscribes alarms on every Connected entry without first
+    ///     calling Unsubscribe, and the driver object (and its projection) survives the in-place
+    ///     reconnect. Each SubscribeAlarmsAsync used to start a fresh, never-cancelled poll loop —
+    ///     so after N reconnects there were N live loops all polling the device and all firing the
+    ///     same raise/clear transition, producing DUPLICATE alarm events.
+    ///
+    ///     This test simulates two re-subscribes (one reconnect) against the same source, then
+    ///     drives ONE device raise. After the collapse-to-single-loop fix exactly one loop is alive
+    ///     so the raise must fire exactly once. Before the fix both loops fire it ⇒ two events.
+    /// </summary>
+    [Fact]
+    public async Task Resubscribe_collapses_to_single_loop_no_duplicate_raise()
+    {
+        var (drv, factory) = NewDriver(alarmsEnabled: true);
+        factory.Customise = () => new FakeFocasClient();
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var raises = new List<AlarmEventArgs>();
+        drv.OnAlarmEvent += (_, e) =>
+        {
+            // Count only the raise (the initial 0->1) — clears wrap the message in "(cleared)".
+            if (!e.Message.Contains("cleared")) lock (raises) raises.Add(e);
+        };
+
+        // First subscribe creates + connects the per-device client and starts polling. Wait for
+        // it + a couple empty-list ticks so the loop's LastByDevice baseline is seeded empty.
+        var sub1 = await drv.SubscribeAlarmsAsync([], CancellationToken.None);
+        await WaitFor(() => factory.Clients.Count > 0, TimeSpan.FromSeconds(3));
+        await Task.Delay(120);
+
+        // Second subscribe = the actor re-subscribing across a reconnect. Its loop reuses the same
+        // connected DeviceState.Client (EnsureConnectedAsync), so it polls the same alarm list.
+        var sub2 = await drv.SubscribeAlarmsAsync([], CancellationToken.None);
+        await Task.Delay(120); // let sub2's loop seed its own empty LastByDevice baseline
+
+        // One device raise transition. Add to every created client so that whichever instance the
+        // live loop(s) poll, the raise is observed (EnsureConnectedAsync may have churned clients).
+        foreach (var c in factory.Clients)
+            c.Alarms.Add(new FocasActiveAlarm(500, FocasAlarmType.Overtravel, 1, "Axis 1 overtravel"));
+
+        // Wait until at least one raise is observed, then give any leaked second loop ample time
+        // (well past several 30ms poll intervals) to ALSO fire its duplicate before we assert.
+        await WaitFor(() => { lock (raises) return raises.Count > 0; }, TimeSpan.FromSeconds(3));
+        await Task.Delay(200);
+
+        await drv.UnsubscribeAlarmsAsync(sub1, CancellationToken.None);
+        await drv.UnsubscribeAlarmsAsync(sub2, CancellationToken.None);
+        await drv.ShutdownAsync(CancellationToken.None);
+
+        lock (raises)
+        {
+            raises.Count.ShouldBe(1,
+                "exactly one poll loop must survive a re-subscribe; a leaked loop fires a duplicate raise");
+        }
+    }
+
     /// <summary>Verifies that tick diffs raises and clears without polling loop.</summary>
     [Fact]
     public async Task Tick_diffs_raises_and_clears_without_polling_loop()