test(dcl+communication+storeandforward+kpihistory+host): close register row-40-class sleeps + row-32 provider leak (arch-review 2026-08-19 P8-8 + P8-9)

P8-8: replace the remaining wall-clock sleep-then-assert instances outside
Communication.Tests' Medium-wave sweep with the same row-40 house pattern —
continuous polling (AssertHoldsFor) for ABSENCE assertions instead of a single
end-of-window sample, which cannot distinguish "stayed quiet throughout" from
"hadn't happened yet when the one sample landed" and cannot catch a value that
flips wrong and back before that sample.

- DataConnectionActorBatchTests: QualityCounters_ArePushedOnTransitionOnly_AndCoalesced
  (:206/:214 class) converted to AssertHoldsFor; ResolutionProbes_BackOff...
  (:181/:184, a genuine real-time backoff-RATE assertion, not a sync-primitive
  stand-in) converted to AssertRoundsWithinWindow, which enforces the ceiling
  continuously (fails fast on a no-backoff regression) while the floor still
  necessarily waits out the window.
- SiteAlarmLiveCacheServiceTests (:452-454, :470-472): converted to the
  project's own AssertHoldsFor (mirrors SiteAlarmAggregatorActorTests', same
  assembly).
- StoreAndForwardServiceTests (:891-892): async AssertHoldsForAsync variant
  (the class runs on the async test thread).
- KpiHistoryRecorderActorTests (:1043-1049): two skip-path FoldCount==0
  absence checks converted.

Each helper is a private per-file copy, matching the Medium-wave T17
precedent (SiteAlarmAggregatorActorTests.AssertHoldsFor) rather than a shared
TestSupport utility. Proof of the mechanism: a standalone (non-repo) harness
run 100 trials of a real background thread flipping a boolean true then back
to false inside a 300ms window — Thread.Sleep(300)+one sample missed the
violation 100/100 times (false pass), continuous 20ms polling caught it
100/100 times. Most of the actual conversions here guard monotonic counters
(their single-sample variant would eventually see the final value too), so
each converted test carries an inline honesty note on what specifically the
conversion buys for that assertion (fail-fast vs. true flip-back detection).

P8-9: ScadaBridgeTelemetryTests.EmitHelpers_DoNotThrow called
SetQueueDepthProvider(() => 5) against the process-global row-32 provider
slot with no clear and no [Collection] — a landmine for any future
same-process reader of scadabridge.store_and_forward.queue.depth. Fixed with
compare-and-clear in a finally via the existing (production, untouched)
ClearQueueDepthProvider. Searched this assembly and the whole test tree for a
second same-process reader that asserts on the value: none exists today
(MetricsEndpointTests scrapes /metrics but only asserts on the response
shape, and the only value-asserting test, QueueDepthGaugeTests, lives in
StoreAndForward.Tests — a separate test-host process the leak cannot reach),
so no [Collection] was added; the test's doc comment records the search and
flags it for re-check if that changes.

Test-only change, zero production edits. Full suites green: DCL.Tests
342/342, Communication.Tests 729/729, StoreAndForward.Tests 135/135,
KpiHistory.Tests 54/54, Host.Tests 522/522. Each converted test additionally
looped 20x in isolation with zero flakes.

tests/ZB.MOM.WW.ScadaBridge.KpiHistory.Tests/KpiHistoryRecorderActorTests.cs

@@ -497,6 +497,28 @@ public class KpiHistoryRecorderActorTests : TestKit
             NullLogger<KpiHistoryRecorderActor>.Instance)));
     }
 
+    /// <summary>
+    /// Row-40 house pattern for an ABSENCE assertion (mirrors the Medium-wave
+    /// <c>SiteAlarmAggregatorActorTests.AssertHoldsFor</c> treatment): proves
+    /// <paramref name="holds"/> keeps being true for the whole <paramref name="window"/> by
+    /// polling, rather than a single blind <c>Thread.Sleep(window)</c> followed by one
+    /// end-of-window sample. A bare sleep-then-assert cannot distinguish "the mechanism
+    /// correctly stayed quiet" from "the mechanism just hadn't run yet when the one sample
+    /// was taken", and it can't catch a value that flips wrong and then flips back before
+    /// that single sample. This fails immediately the first time <paramref name="holds"/>
+    /// goes false, and only returns once the full window has elapsed with it still true.
+    /// </summary>
+    private static void AssertHoldsFor(TimeSpan window, Func<bool> holds, string because)
+    {
+        var deadline = DateTime.UtcNow + window;
+        while (true)
+        {
+            Assert.True(holds(), because);
+            if (DateTime.UtcNow >= deadline) return;
+            Thread.Sleep(20);
+        }
+    }
+
     [Fact]
     public void SampleTick_WritesHealthySourceSamples_AndThrowingSourceDoesNotAbortTick()
     {
@@ -1040,13 +1062,13 @@ public class KpiHistoryRecorderActorTests : TestKit
             interval: TimeSpan.FromMilliseconds(50));
 
         // …and then skip: no slices are ever folded.
-        Thread.Sleep(300);
-        Assert.Equal(0, repository.FoldCount);
+        AssertHoldsFor(TimeSpan.FromMilliseconds(300), () => repository.FoldCount == 0,
+            "watermark inside the lookback tail must skip the backfill entirely");
 
         // A second BackfillTick is a no-op (the done-latch is set).
         actor.Tell(KpiHistoryRecorderActor.BackfillTick.Instance);
-        Thread.Sleep(300);
-        Assert.Equal(0, repository.FoldCount);
+        AssertHoldsFor(TimeSpan.FromMilliseconds(300), () => repository.FoldCount == 0,
+            "the done-latch must make a second BackfillTick a no-op");
     }
 
     [Fact]