Merge #602 stability: FOCAS/AbLegacy loop joins on shutdown, Postgres untyped string binds, MTConnect pump generation, MQTT birth-typed writes + QoS1 plain writes + claim backoff

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/AbLegacyDriver.cs

@@ -229,7 +229,7 @@ public sealed class AbLegacyDriver : IDriver, IReadable, IWritable, ITagDiscover
                 {
                     state.ProbeCts = new CancellationTokenSource();
                     var ct = state.ProbeCts.Token;
-                    _ = Task.Run(() => ProbeLoopAsync(state, ct), ct);
+                    state.ProbeTask = Task.Run(() => ProbeLoopAsync(state, ct), ct);
                 }
             }
             _health = new DriverHealth(DriverState.Healthy, DateTime.UtcNow, null);
@@ -245,10 +245,13 @@ public sealed class AbLegacyDriver : IDriver, IReadable, IWritable, ITagDiscover
             // handles alive. Mirrors the body of ShutdownAsync without awaiting the poll engine
             // (nothing has been subscribed yet at init time).
             foreach (var state in _devices.Values)
-            {
                 try { state.ProbeCts?.Cancel(); } catch { }
+            JoinProbeLoopsSync();
+            foreach (var state in _devices.Values)
+            {
                 state.ProbeCts?.Dispose();
                 state.ProbeCts = null;
+                state.ProbeTask = null;
                 state.DisposeRuntimes();
             }
             _devices.Clear();
@@ -266,15 +269,45 @@ public sealed class AbLegacyDriver : IDriver, IReadable, IWritable, ITagDiscover
         await InitializeAsync(driverConfigJson, cancellationToken).ConfigureAwait(false);
     }
 
+    /// <summary>Upper bound on how long shutdown waits for the probe loops to observe cancellation.</summary>
+    internal static readonly TimeSpan LoopJoinTimeout = TimeSpan.FromSeconds(5);
+
+    /// <summary>
+    ///     Synchronous bounded join of the (already-cancelled) probe loops for the sync teardown paths.
+    ///     The loop body uses <c>ConfigureAwait(false)</c> throughout, so blocking here cannot deadlock.
+    /// </summary>
+    private void JoinProbeLoopsSync()
+    {
+        var loops = _devices.Values.Select(d => d.ProbeTask).OfType<Task>().ToArray();
+        if (loops.Length == 0) return;
+        try { Task.WaitAll(loops, LoopJoinTimeout); }
+        catch (AggregateException) { /* loops observe cancellation; a fault is not actionable at teardown */ }
+    }
+
     /// <inheritdoc />
     public async Task ShutdownAsync(CancellationToken cancellationToken)
     {
         await _poll.DisposeAsync().ConfigureAwait(false);
+        // STAB-6: cancel the probe loops, JOIN them (bounded), then dispose the CTSs and runtimes.
+        // The loop used to be fire-and-forget, so one parked in a probe-runtime create/read could
+        // outlive shutdown and keep a libplctag handle alive past DisposeRuntimes.
+        foreach (var state in _devices.Values)
+            try { state.ProbeCts?.Cancel(); } catch { }
+        var loops = _devices.Values.Select(d => d.ProbeTask).OfType<Task>().ToList();
+        if (loops.Count > 0)
+        {
+            var all = Task.WhenAll(loops);
+            var finished = await Task.WhenAny(all, Task.Delay(LoopJoinTimeout, CancellationToken.None)).ConfigureAwait(false);
+            if (finished != all)
+                _logger.LogWarning(
+                    "AbLegacy shutdown: {Count} probe loop(s) did not stop within {Timeout}; proceeding with teardown. Driver={DriverInstanceId}",
+                    loops.Count, LoopJoinTimeout, _driverInstanceId);
+        }
         foreach (var state in _devices.Values)
         {
-            try { state.ProbeCts?.Cancel(); } catch { }
             state.ProbeCts?.Dispose();
             state.ProbeCts = null;
+            state.ProbeTask = null;
             state.DisposeRuntimes();
         }
         _devices.Clear();
@@ -908,10 +941,13 @@ public sealed class AbLegacyDriver : IDriver, IReadable, IWritable, ITagDiscover
         // can't poison the rest of the disposal chain.
         try { _poll.DisposeAsync().ConfigureAwait(false).GetAwaiter().GetResult(); } catch { }
         foreach (var state in _devices.Values)
-        {
             try { state.ProbeCts?.Cancel(); } catch { }
+        JoinProbeLoopsSync();
+        foreach (var state in _devices.Values)
+        {
             state.ProbeCts?.Dispose();
             state.ProbeCts = null;
+            state.ProbeTask = null;
             state.DisposeRuntimes();
         }
         _devices.Clear();
@@ -1037,6 +1073,11 @@ public sealed class AbLegacyDriver : IDriver, IReadable, IWritable, ITagDiscover
         /// </summary>
         public CancellationTokenSource? ProbeCts { get; set; }
 
+        /// <summary>
+        ///     Gets or sets the probe loop task, retained so shutdown can join it (STAB-6).
+        /// </summary>
+        public Task? ProbeTask { get; set; }
+
         /// <summary>
         ///     Gets or sets a value indicating whether the probe has been initialized.
         /// </summary>