test(historian): justify/tighten the shutdown watch window; single read of RemoveCallCount per poll

tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Historian/ContinuousHistorizationRecorderTests.cs

@@ -609,12 +609,22 @@ public sealed class ContinuousHistorizationRecorderTests : TestKit
         // the queued count moving off 2. Either fires the moment the unfixed recorder books the failure and
         // truncates, so a regression fails in milliseconds rather than after a fixed sleep; only the passing
         // case pays the full window.
+        //
+        // 1s is the window, and it is already generous headroom rather than a guess: everything it waits on
+        // is prompt on this fixture — the cancellation of the writer's `Task.Delay(Timeout.Infinite, ct)` is
+        // essentially synchronous (and `writer.Cancelled` above has already fired), the fold that would
+        // truncate runs immediately behind it, and the recorder's own cadence here is a 20ms drain interval
+        // with a 20-50ms backoff. The unfixed recorder trips this in ~150ms including startup, so the
+        // remaining ~6x is CI-load slack, not mechanism.
         var watch = Stopwatch.StartNew();
-        while (watch.Elapsed < TimeSpan.FromSeconds(2))
+        while (watch.Elapsed < TimeSpan.FromSeconds(1))
         {
+            // Read once per iteration: the condition and its failure message must report the SAME
+            // observation, or a red run names a count that is not the one that tripped.
+            int removeCalls = outbox.RemoveCallCount;
             Assert.True(
-                outbox.RemoveCallCount == 0,
-                $"the cancelled pass acked: RemoveAsync ran {outbox.RemoveCallCount}x, truncating the queue");
+                removeCalls == 0,
+                $"the cancelled pass acked: RemoveAsync ran {removeCalls}x, truncating the queue");
             int queued = await outbox.CountAsync(default);
             Assert.True(queued == 2, $"the cancelled pass changed the queue depth: expected 2, saw {queued}");
             await Task.Delay(25);