Resolve Worker.Tests-001 and Worker.Tests-002 code-review findings

Worker.Tests-001: StaMessagePump had no direct unit test. Added
Sta/StaMessagePumpTests.cs — 8 STA-thread facts covering WaitForWorkOrMessages
(wake-event signalled before/during the wait, timeout expiry, zero-timeout
fast path, the QS_ALLINPUT posted-message wake path) and PumpPendingMessages
drain counting.

Worker.Tests-002: no test drove a COM event through the integrated
sink -> mapper -> queue path. Added MxAccess/MxAccessBaseEventSinkTests.cs —
5 facts driving OnDataChange, OnWriteComplete, OperationComplete and
OnBufferedDataChange through a real MxAccessBaseEventSink + mapper + queue and
asserting the converted WorkerEvent lands in MxAccessEventQueue. The four COM
event handlers were widened private -> internal and InternalsVisibleTo for
MxGateway.Worker.Tests was added, mirroring MxAccessAlarmEventSink's existing
test seam; no worker behavior changes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/MxGateway.Worker/MxAccess/MxAccessBaseEventSink.cs

@@ -65,7 +65,14 @@ public sealed class MxAccessBaseEventSink : IMxAccessEventSink
         sessionId = string.Empty;
     }
 
-    private void OnDataChange(
+    /// <summary>
+    ///     Handles the MXAccess <c>OnDataChange</c> COM event: converts the
+    ///     event arguments to a protobuf <see cref="Proto.MxEvent"/> and enqueues
+    ///     it. Subscribed to the COM object's event in <see cref="Attach"/>.
+    ///     Exposed <c>internal</c> so unit tests can drive the integrated
+    ///     sink → mapper → queue path without a live MXAccess COM event source.
+    /// </summary>
+    internal void OnDataChange(
         int hLMXServerHandle,
         int phItemHandle,
         object pvItemValue,
@@ -84,7 +91,11 @@ public sealed class MxAccessBaseEventSink : IMxAccessEventSink
             statuses));
     }
 
-    private void OnWriteComplete(
+    /// <summary>
+    ///     Handles the MXAccess <c>OnWriteComplete</c> COM event. Exposed
+    ///     <c>internal</c> as a unit-test seam; see <see cref="OnDataChange"/>.
+    /// </summary>
+    internal void OnWriteComplete(
         int hLMXServerHandle,
         int phItemHandle,
         ref MXSTATUS_PROXY[] pVars)
@@ -97,7 +108,11 @@ public sealed class MxAccessBaseEventSink : IMxAccessEventSink
             statuses));
     }
 
-    private void OperationComplete(
+    /// <summary>
+    ///     Handles the MXAccess <c>OperationComplete</c> COM event. Exposed
+    ///     <c>internal</c> as a unit-test seam; see <see cref="OnDataChange"/>.
+    /// </summary>
+    internal void OperationComplete(
         int hLMXServerHandle,
         int phItemHandle,
         ref MXSTATUS_PROXY[] pVars)
@@ -110,7 +125,11 @@ public sealed class MxAccessBaseEventSink : IMxAccessEventSink
             statuses));
     }
 
-    private void OnBufferedDataChange(
+    /// <summary>
+    ///     Handles the MXAccess <c>OnBufferedDataChange</c> COM event. Exposed
+    ///     <c>internal</c> as a unit-test seam; see <see cref="OnDataChange"/>.
+    /// </summary>
+    internal void OnBufferedDataChange(
         int hLMXServerHandle,
         int phItemHandle,
         MxDataType dtDataType,

src/MxGateway.Worker/MxGateway.Worker.csproj

@@ -14,6 +14,10 @@
     <PackageReference Include="Polly.Core" Version="8.6.6" />
   </ItemGroup>
 
+  <ItemGroup>
+    <InternalsVisibleTo Include="MxGateway.Worker.Tests" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="..\MxGateway.Contracts\MxGateway.Contracts.csproj" />
   </ItemGroup>