fix(worker): classify ack interop failures at the COM call; ignore late completions

Address review of the #164-#166 fixes:

- The HRESULT check could not tell interop from programming errors
  (a managed ArgumentException already defaults to 0x80070057). Wrap each
  MXAccess call (AuthenticateUser, AddItem, Advise, Write) in a narrow
  filter that converts an interop failure to a private marker exception,
  and catch only that marker, so exceptions from the writer's own code
  (argument checks, caching, the pump) propagate.
- A late OnWriteComplete for a dropped handle recreated the cache entry
  that DropItem removed. The writer now records completions only for item
  handles it holds on its live registration.
- The item-handle-reuse probe now asserts that handles within one
  registration strictly increase, so a rerun is a regression check.

Refs #164, #165, #166

Claude-Session: https://claude.ai/code/session_016J6isfcgqy4SB2RK3ZvFvT

src/ZB.MOM.WW.MxGateway.Worker.Tests/Probes/ItemHandleReuseProbeTests.cs

@@ -46,6 +46,9 @@ public sealed class ItemHandleReuseProbeTests
     private readonly ITestOutputHelper output;
     private readonly List<string> log = new List<string>();
 
+    // Item handles returned on the first registration, in the order they were handed out.
+    private readonly List<int> firstRegistrationHandles = new List<int>();
+
     /// <summary>Initializes a new instance of the <see cref="ItemHandleReuseProbeTests"/> class.</summary>
     /// <param name="output">Test output helper for logging.</param>
     public ItemHandleReuseProbeTests(ITestOutputHelper output)
@@ -76,6 +79,16 @@ public sealed class ItemHandleReuseProbeTests
         {
             throw new InvalidOperationException("Probe failed: " + threadException.Message, threadException);
         }
+
+        // The ack writer's drop-and-re-add mitigation depends on this: within one
+        // registration a handle number is never handed out twice.
+        Assert.Equal((2 * Rounds) + 5, firstRegistrationHandles.Count);
+        for (int i = 1; i < firstRegistrationHandles.Count; i++)
+        {
+            Assert.True(
+                firstRegistrationHandles[i] > firstRegistrationHandles[i - 1],
+                $"Item handle {firstRegistrationHandles[i]} did not increase past {firstRegistrationHandles[i - 1]}; MXAccess reused or reordered item handles within one registration.");
+        }
     }
 
     private void RunProbe()
@@ -90,7 +103,7 @@ public sealed class ItemHandleReuseProbeTests
             // A: the AlarmAckWriter drop path (Advise, then UnAdvise + RemoveItem).
             for (int i = 0; i < Rounds; i++)
             {
-                int h = mx.AddItem(server, AckItem);
+                int h = Held(mx.AddItem(server, AckItem));
                 mx.Advise(server, h);
                 Log($"A{i}: AddItem+Advise {AckItem} -> {h}");
                 mx.UnAdvise(server, h);
@@ -101,28 +114,28 @@ public sealed class ItemHandleReuseProbeTests
             // B: RemoveItem without Advise.
             for (int i = 0; i < Rounds; i++)
             {
-                int h = mx.AddItem(server, AckItem);
+                int h = Held(mx.AddItem(server, AckItem));
                 Log($"B{i}: AddItem {AckItem} -> {h}");
                 mx.RemoveItem(server, h);
                 Log($"B{i}: RemoveItem {h}");
             }
 
             // C: interleave another item to see whether a freed number is handed to any item.
-            int c1 = mx.AddItem(server, AckItem);
+            int c1 = Held(mx.AddItem(server, AckItem));
             Log($"C: AddItem {AckItem} -> {c1}");
             mx.RemoveItem(server, c1);
             Log($"C: RemoveItem {c1}");
-            int c2 = mx.AddItem(server, OtherItem);
+            int c2 = Held(mx.AddItem(server, OtherItem));
             Log($"C: AddItem {OtherItem} -> {c2}");
-            int c3 = mx.AddItem(server, AckItem);
+            int c3 = Held(mx.AddItem(server, AckItem));
             Log($"C: AddItem {AckItem} -> {c3}");
             mx.RemoveItem(server, c2);
             mx.RemoveItem(server, c3);
             Log($"C: RemoveItem {c2}, {c3}");
 
             // D: the same item added twice while the first is still held.
-            int d1 = mx.AddItem(server, AckItem);
-            int d2 = mx.AddItem(server, AckItem);
+            int d1 = Held(mx.AddItem(server, AckItem));
+            int d2 = Held(mx.AddItem(server, AckItem));
             Log($"D: AddItem {AckItem} twice while held -> {d1}, {d2}");
             mx.RemoveItem(server, d1);
             mx.RemoveItem(server, d2);
@@ -159,6 +172,12 @@ public sealed class ItemHandleReuseProbeTests
         }
     }
 
+    private int Held(int itemHandle)
+    {
+        firstRegistrationHandles.Add(itemHandle);
+        return itemHandle;
+    }
+
     private void Log(string line)
     {
         log.Add(DateTime.Now.ToString("HH:mm:ss.fff") + " " + line);