test(site-runtime): HandshakeResetEchoTests — label the legacy pin as permanent behaviour (#36 review)

Claude-Session: https://claude.ai/code/session_01XPsuy2ZZ5Gbyfpt8PrK5BV

tests/ZB.MOM.WW.ScadaBridge.SiteRuntime.Tests/Actors/HandshakeResetEchoTests.cs

@@ -84,7 +84,12 @@ public class HandshakeResetEchoTests : TestKit, IDisposable
     private static IReadOnlyDictionary<string, string?> Values(int batchId)
         => new Dictionary<string, string?> { ["MoveOutBatchID"] = AttributeValueCodec.Encode(batchId) };
 
-    /// <summary>The defect, as documentation: the legacy overload answers from the stale cache.</summary>
+    /// <summary>
+    /// Pins the PERMANENT legacy behaviour, not a bug awaiting a fix: the six-argument overload is
+    /// deliberately unchanged (deployed scripts keep their semantics) and answers from the stale
+    /// cache — callers migrate to the reset-aware overload instead. Never "fix" the fast-path in
+    /// place; delete this test only if the legacy overload itself is removed.
+    /// </summary>
     [Fact]
     public async Task LegacyOverload_FastPathsOnThePreviousRunsCachedTrue()
     {
@@ -127,11 +132,13 @@ public class HandshakeResetEchoTests : TestKit, IDisposable
         // Only now the batch + trigger.
         var batch = dcl.ExpectMsg<WriteTagBatchRequest>(TimeSpan.FromSeconds(5));
         Assert.Equal(TriggerTag, batch.TriggerTagPath);
+        // TriggerValue may arrive boxed as bool or as its already-encoded string; normalise both sides.
         Assert.Equal(AttributeValueCodec.Encode(true), AttributeValueCodec.Encode(batch.TriggerValue));
         Assert.True(batch.Values.ContainsKey(BatchTag));
         dcl.Reply(new WriteTagBatchResponse(batch.CorrelationId, true, null, DateTimeOffset.UtcNow));
 
-        // Still pending: the cache now holds False.
+        // Still pending: the cache now holds False, and nothing can complete the call until the
+        // TagValueUpdate below is sent — no race here, only a documented intermediate state.
         Assert.False(call.IsCompleted);
 
         // The device completes THIS request.