diff --git a/code-reviews/Driver.Calculation/findings.md b/code-reviews/Driver.Calculation/findings.md
index 3269936f..0f9ec50c 100644
--- a/code-reviews/Driver.Calculation/findings.md
+++ b/code-reviews/Driver.Calculation/findings.md
@@ -262,11 +262,15 @@ run so a tag dropped mid-evaluation discards its result rather than publishing i
 
 RED first, two tests, both failing against the pre-fix code:
 `A_dependency_arrival_does_not_run_the_script_on_the_callers_thread` (the publish — which can only happen
-after the script ran — landed on the caller's own thread id) and
+after the script ran — landed on the caller's own stack, inside the callback) and
 `A_slow_script_blocks_neither_the_dependency_callback_nor_a_concurrent_read` (a 600 ms busy-wait script:
 the callback took 1.21 s, and `ReadAsync`, which needs the same state lock, was stuck behind it). Both
 carry a positive control asserting the value still computes and publishes, so neither can pass against a
-driver that simply evaluates nothing.
+driver that simply evaluates nothing. ⚠️ The first test's original form compared the publish's **thread id**
+against the caller's and was itself flaky (1 failure in 6 runs): the pump is free to reuse the pooled thread
+the test released while awaiting, so an id match means nothing. It asserts on a thread-local flag set for
+exactly the callback window instead — which is exact, and was re-falsified by making `SchedulePump` run the
+pump synchronously (red immediately, then reverted).
 
 Known trade, documented rather than hidden: the pending queue is unbounded. Under sustained arrival
 pressure the previous inline path applied backpressure by blocking the mux actor — which is the defect —
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation.Tests/CalculationDriverTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation.Tests/CalculationDriverTests.cs
index 5f9a9160..35945878 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation.Tests/CalculationDriverTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation.Tests/CalculationDriverTests.cs
@@ -118,28 +118,33 @@ public sealed class CalculationDriverTests
     ///     <c>DependencyConsumerMuxAdapter.OnDependencyValueChanged</c> — i.e. on an Akka actor's own
     ///     dispatcher thread. Evaluating there means a script run (bounded only by <c>RunTimeout</c>,
     ///     default 2 s) occupies that thread, so the callback must queue the work and return instead.
-    ///     <para>The publish is the observable: it can only happen after the script ran, so a publish on
-    ///     the caller's own thread proves the script ran inline. The value assertion is the positive
-    ///     control — without it this would pass just as happily against a driver that evaluates nothing.</para>
+    ///     <para>The publish is the observable: it can only happen after the script ran, so a publish that
+    ///     lands on the caller's stack <em>between</em> entering and leaving the callback proves the script
+    ///     ran inline. A thread-local flag set for exactly that window is the exact test — comparing thread
+    ///     <i>ids</i> is not, because the pump is free to reuse the pooled thread the test released while
+    ///     waiting, which makes an id match mean nothing. The value assertion is the positive control:
+    ///     without it this would pass just as happily against a driver that evaluates nothing at all.</para>
     /// </summary>
     [Fact]
     public async Task A_dependency_arrival_does_not_run_the_script_on_the_callers_thread()
     {
         var (driver, published, _) = Build(
             CalcTag("calc/e/dbl", "return (double)ctx.GetTag(\"src/a\").Value * 2.0;"));
-        var publishThreadId = 0;
-        driver.OnDataChange += (_, _) => publishThreadId = Environment.CurrentManagedThreadId;
+        using var insideCallback = new ThreadLocal<bool>();
+        var publishedInline = false;
+        driver.OnDataChange += (_, _) => { if (insideCallback.Value) publishedInline = true; };
         await driver.InitializeAsync("{}", TestContext.Current.CancellationToken);
 
-        var callerThreadId = Environment.CurrentManagedThreadId;
+        insideCallback.Value = true;
         driver.OnDependencyValue("src/a", 5.0, StatusGood, DateTime.UtcNow);
+        insideCallback.Value = false;
 
-        (await WaitUntil(() => !published.IsEmpty, TimeSpan.FromSeconds(5)))
+        (await WaitUntil(() => !published.IsEmpty, TimeSpan.FromSeconds(10)))
             .ShouldBeTrue("the queued evaluation must still compute and publish the value");
         published.TryDequeue(out var e).ShouldBeTrue();
         e!.Snapshot.Value.ShouldBe(10.0);
 
-        publishThreadId.ShouldNotBe(callerThreadId,
+        publishedInline.ShouldBeFalse(
             "the calc script must run on the driver's own evaluation pump, never on the mux callback thread");
     }