Resolve Worker-001, Worker-002, Worker-003 code-review findings

Worker-001: WnWrapAlarmConsumer armed a System.Threading.Timer whose OnPoll
callback ran GetXmlCurrentAlarms2 on a thread-pool thread against the
Apartment-threaded wnwrap COM object, which can deadlock on cross-apartment
marshaling. Removed the pollTimer/pollIntervalMs fields, OnPoll, the
poll-interval constructor parameter, and the timer arm/disposal. Polls are
driven externally by the STA via StaRuntime.InvokeAsync(PollOnce).

Worker-002: RunHeartbeatLoopAsync delayed a full HeartbeatInterval before
the first heartbeat. Restructured so the first beat is sent immediately on
entering the loop and the delay applies only between subsequent beats.

Worker-003: ProcessCommandAsync silently returned without a reply when
_state was not a command-serving state after dispatch. Both drop sites now
log a WorkerCommandResultDropped diagnostic with correlation_id via
IWorkerLogger; _state is now volatile.

Three pre-existing tests that asserted strict frame ordering were updated to
tolerate an interleaved first heartbeat (Worker-002 consequence).

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

src/MxGateway.Worker.Tests/Ipc/WorkerPipeClientTests.cs

@@ -77,7 +77,9 @@ public sealed class WorkerPipeClientTests
             },
         });
 
-        WorkerEnvelope shutdownAck = await reader.ReadAsync();
+        WorkerEnvelope shutdownAck = await ReadUntilAsync(
+            reader,
+            WorkerEnvelope.BodyOneofCase.WorkerShutdownAck);
         Assert.Equal(WorkerEnvelope.BodyOneofCase.WorkerShutdownAck, shutdownAck.BodyCase);
         await clientTask;
     }
@@ -120,7 +122,9 @@ public sealed class WorkerPipeClientTests
         Assert.Equal(WorkerEnvelope.BodyOneofCase.WorkerReady, (await reader.ReadAsync()).BodyCase);
         await writer.WriteAsync(CreateShutdown());
 
-        Assert.Equal(WorkerEnvelope.BodyOneofCase.WorkerShutdownAck, (await reader.ReadAsync()).BodyCase);
+        Assert.Equal(
+            WorkerEnvelope.BodyOneofCase.WorkerShutdownAck,
+            (await ReadUntilAsync(reader, WorkerEnvelope.BodyOneofCase.WorkerShutdownAck)).BodyCase);
         await clientTask;
     }
 
@@ -143,6 +147,25 @@ public sealed class WorkerPipeClientTests
         await Assert.ThrowsAsync<TimeoutException>(async () => await client.RunAsync(workerOptions));
     }
 
+    /// <summary>
+    ///     Reads frames until one matching the expected body case is found,
+    ///     skipping interleaved heartbeats (the first heartbeat is emitted
+    ///     immediately on entering the heartbeat loop — see Worker-002).
+    /// </summary>
+    private static async Task<WorkerEnvelope> ReadUntilAsync(
+        WorkerFrameReader reader,
+        WorkerEnvelope.BodyOneofCase expectedBody)
+    {
+        while (true)
+        {
+            WorkerEnvelope envelope = await reader.ReadAsync();
+            if (envelope.BodyCase == expectedBody)
+            {
+                return envelope;
+            }
+        }
+    }
+
     private static WorkerPipeSession CreateSession(
         Stream stream,
         WorkerFrameProtocolOptions options)