Fix unit stress flakes in JumpList and QueryCache threading tests

tests/Reactor.Tests/Core/QueryCacheThreadingTests.cs

@@ -19,8 +19,11 @@ public class QueryCacheThreadingTests
     // tests finish in milliseconds; on shared CI runners (virtualized cores,
     // bursty scheduling) flushing the Task scheduler after cancellation can
     // stretch unpredictably. A generous ceiling kills flakes without weakening
-    // the deadlock guarantee.
-    private static readonly TimeSpan DrainTimeout = TimeSpan.FromSeconds(60);
+    // the deadlock guarantee. Bumped 60s→120s after a 1-in-1000 stress hit on
+    // Concurrent_Subscribe_Unsubscribe_Converges_To_Zero where the workload is
+    // pure lock-bound bookkeeping (no eviction is reachable in 60s given the
+    // 5-minute default CacheTime) — i.e. the timeout was scheduler-induced.
+    private static readonly TimeSpan DrainTimeout = TimeSpan.FromSeconds(120);
 
     // ════════════════════════════════════════════════════════════════
     //  Concurrent Set + TryGet — no torn reads

tests/Reactor.Tests/JumpListItemTests.cs

@@ -182,6 +182,7 @@ public void TryResolve_Throws_On_Null_Map()
 /// Spec 036 §11.3 — JumpList static state. We don't exercise the live shell
 /// here (that's a selftest fixture); only the public state surface.
 /// </summary>
+[Collection("JumpListGlobals")]
 public class JumpListStateTests
 {
     [Fact]

tests/Reactor.Tests/JumpListUpdateValidationTests.cs

@@ -12,8 +12,12 @@ namespace Microsoft.UI.Reactor.Tests;
 /// caller-error gates that run synchronously before any platform call.
 ///
 /// Each test uses <c>JumpList.ResetForTests()</c> to isolate the static
-/// state.
+/// state. The <c>JumpListGlobals</c> collection serializes these tests
+/// with <see cref="JumpListStateTests"/> so the shared static
+/// <c>JumpList.AppUserModelId</c> is not clobbered by a concurrent
+/// <c>ResetForTests()</c> in another class.
 /// </summary>
+[Collection("JumpListGlobals")]
 public class JumpListUpdateValidationTests : IDisposable
 {
     public JumpListUpdateValidationTests() => JumpList.ResetForTests();