Stress fixes: Cluster F poll, leak baseline timeout bump (#399)

Two independent stress-flake fixes per INVESTIGATION.md session 4
follow-up to PR #397:

Cluster F (4/1000 hits in run 26351376710) — FloatingTitleBar_PaneBodyVisible
asserted body TextBlock visibility after a single Harness.Render()
following DockFloatingWindow.Open. Chrome (TabView, TitleBar absence,
TabStripFooter) materializes on that first pump, but the inner pane
content lags one or two pumps behind on a loaded CI runner. Same
realization-race family as Cluster C; apply the same poll pattern
(2s budget, 50ms between pumps) and annotate the check name with the
observed body count for future-hit diagnostics.

Cluster T-new (2/1000 hits) — EventSubscriptionLeakBaseline timing out
at its 30s override. Local timing measurement across 3 fresh-process
runs: 14.5 / 15.6 / 15.4 s (avg 15.2s) on a dev box. The fixture is
100 mount/unmount cycles x 2 Harness.Render() = 200 renders + 200
reconcile passes; the work itself is substantial. CI VMs under load
have been measured at 2-4x slowdown elsewhere in the doc, easily
overshooting the 30s budget. Not a hang — just budget vs CI variance.
Bump FixtureTimeout to 60s (~4x local baseline) with a comment block
explaining the math.

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

Author: codemonkeychris

tests/Reactor.AppTests.Host/SelfTest/Fixtures/NativeDockingReliabilityFixture.cs

@@ -523,7 +523,12 @@ public override async Task RunAsync()
     /// </summary>
     internal class EventSubscriptionLeakBaseline(Harness h) : SelfTestFixtureBase(h)
     {
-        public override TimeSpan FixtureTimeout => TimeSpan.FromSeconds(30);
+        // 100 mount/unmount cycles × 2 Harness.Render() each = 200 renders + 200
+        // reconcile passes. Locally this runs ~15s; CI VMs under contention have
+        // been measured at 2-4× slower per INVESTIGATION.md Cluster T, easily
+        // overshooting the prior 30s budget on a heavy iteration. The cap exists
+        // to catch a hung fixture, not to set a perf target.
+        public override TimeSpan FixtureTimeout => TimeSpan.FromSeconds(60);
 
         public override async Task RunAsync()
         {

tests/Reactor.AppTests.Host/SelfTest/Fixtures/NativeDockingSmokeFixture.cs

@@ -1652,9 +1652,18 @@ public override async Task RunAsync()
                 H.Check("FloatingTitleBar_TabViewHasStripFooter",
                     tabViews.Count == 1 && tabViews[0].TabStripFooter is not null);
 
-                // Pane body must be reachable.
+                // Pane body must be reachable. Chrome (TabView etc.) materializes on
+                // the first render pump after Open(), but on a loaded CI runner the
+                // inner content TextBlock can lag one or two pumps behind. Poll for
+                // up to 2s — see INVESTIGATION.md Cluster F.
                 var bodyTexts = FindAllInTree<TextBlock>(content, t => t.Text == "floating-tb-body");
-                H.Check("FloatingTitleBar_PaneBodyVisible", bodyTexts.Count >= 1);
+                var deadline = Environment.TickCount64 + 2_000;
+                while (bodyTexts.Count < 1 && Environment.TickCount64 < deadline)
+                {
+                    await Harness.Render(50);
+                    bodyTexts = FindAllInTree<TextBlock>(content, t => t.Text == "floating-tb-body");
+                }
+                H.Check($"FloatingTitleBar_PaneBodyVisible (bodies={bodyTexts.Count})", bodyTexts.Count >= 1);
 
                 floatingWindow.Close();
                 await Harness.Render();