fix(selftest): pump-until guard for GotFocus_FiresOnA (#182)

The fixed two-pump guard added in #152 (and the same shape applied in
#139/#149 for TabView/RadioButtons/PasswordBox) still flaked at ~0.3%
across a 1000x sweep — 2 hits in 651 runs, both on `GotFocus_FiresOnA`.
The number of dispatcher ticks before programmatic Focus() raises
GotFocus isn't bounded, so any fixed pump count is a guess.

Replace the fixed pumps with a pump-until-counter-updates loop, capped
at 10 iterations (~200ms) to fail fast if the event genuinely never
fires. Applied to both focus transitions in the fixture.

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

Author: codemonkeychris

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

@@ -127,16 +127,17 @@ public override async Task RunAsync()
             H.Check("GotLostFocus_ControlsFound", tbA is not null && tbB is not null);
 
             tbA?.Focus(FocusState.Programmatic);
-            // GotFocus can be raised via the dispatcher rather than synchronously
-            // in Focus() (same shape as the TabView/RadioButtons/PasswordBox flake
-            // fixed in #139/#149). Pump twice so the queued event lands.
-            await Harness.Render();
-            await Harness.Render();
+            // GotFocus is raised via the dispatcher, and the number of ticks
+            // before it lands isn't bounded — a fixed two-pump guard (#152)
+            // still flaked at ~0.3% across a 1000x sweep. Pump until the
+            // counter updates instead of guessing a count.
+            for (int i = 0; i < 10 && gotA == 0; i++)
+                await Harness.Render();
             H.Check("GotFocus_FiresOnA", gotA == 1 && lostA == 0);
 
             tbB?.Focus(FocusState.Programmatic);
-            await Harness.Render();
-            await Harness.Render();
+            for (int i = 0; i < 10 && gotB == 0; i++)
+                await Harness.Render();
             H.Check("LostFocus_FiresOnA", lostA == 1);
             H.Check("GotFocus_FiresOnB", gotB == 1);
         }