Skip attach E2E test at discovery time on Windows PowerShell

CanAttachScriptWithPathMappings wedges during the per-test InitializeAsync
(PSES debug-adapter server startup) on in-box Windows PowerShell since the
windows-2025-vs2026 runner image refresh, riding the job timeout in CI.

The prior in-body Skip.If(IsWindowsPowerShell) never fired because xUnit runs
IAsyncLifetime.InitializeAsync before the test body, and that setup is where
the hang occurs. Add a SkippableFact subclass that sets Skip in its
constructor so xUnit skips the test at discovery time, before it instantiates
the class or runs InitializeAsync. The SkippableFact discoverer is retained so
the runtime Constrained Language Mode skip still works off-Windows.

See #2323.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: andyleejordan

test/PowerShellEditorServices.Test.E2E/DebugAdapterProtocolMessageTests.cs

@@ -630,16 +630,16 @@ public async Task CanLaunchScriptWithNewChildAttachSessionAsJob()
             await terminatedTcs.Task;
         }
 
-        [SkippableFact(Timeout = 15000)]
+        // NOTE: This passes against PowerShell Core but hangs against in-box Windows
+        // PowerShell since the windows-2025-vs2026 runner image moved from 20260608 to
+        // 20260614, where it wedges during server setup and rides the job timeout. The
+        // skip must happen at discovery time (via the attribute) rather than with an
+        // in-body Skip.If, because xUnit runs InitializeAsync (which is where the hang
+        // occurs) before the test body. Skipped on Windows PowerShell pending a real
+        // fix; see https://github.com/PowerShell/PowerShellEditorServices/issues/2323.
+        [SkippableFactOnWindowsPowerShell(Timeout = 15000)]
         public async Task CanAttachScriptWithPathMappings()
         {
-            // This passes against PowerShell Core but hangs against in-box Windows
-            // PowerShell since the windows-2025-vs2026 runner image moved from
-            // 20260608 to 20260614: the cross-process Debug-Runspace attach wedges
-            // and rides the job timeout. Skipped pending a real fix; see #2323.
-            Skip.If(PsesStdioLanguageServerProcessHost.IsWindowsPowerShell,
-                "Attach wedges on Windows PowerShell since the 20260614 runner image; see #2323.");
-
             Skip.If(PsesStdioLanguageServerProcessHost.RunningInConstrainedLanguageMode,
                 "Breakpoints can't be set in Constrained Language Mode.");
 

test/PowerShellEditorServices.Test.E2E/Hosts/SkippableFactOnWindowsPowerShellAttribute.cs

@@ -0,0 +1,34 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+using Xunit;
+using Xunit.Sdk;
+
+namespace PowerShellEditorServices.Test.E2E;
+
+/// <summary>
+/// A <see cref="SkippableFactAttribute"/> that additionally skips the test at
+/// <em>discovery</em> time when running under in-box Windows PowerShell.
+/// </summary>
+/// <remarks>
+/// A runtime <see cref="Skip.If(bool, string)"/> in the test body cannot prevent
+/// the per-test <c>IAsyncLifetime.InitializeAsync</c> from running first, because
+/// xUnit invokes the lifetime setup (which starts the PSES server) before the
+/// method body. When the hang occurs during that setup, a body-level skip is never
+/// reached. Setting <see cref="FactAttribute.Skip"/> here makes xUnit treat the
+/// test as statically skipped, so it never instantiates the test class or runs
+/// <c>InitializeAsync</c>. The <see cref="SkippableFactAttribute"/> discoverer is
+/// retained so runtime <see cref="Skip"/> calls (e.g. for Constrained Language
+/// Mode) still work when the test is not skipped at discovery time.
+/// </remarks>
+[XunitTestCaseDiscoverer("Xunit.Sdk.SkippableFactDiscoverer", "Xunit.SkippableFact")]
+public sealed class SkippableFactOnWindowsPowerShellAttribute : SkippableFactAttribute
+{
+    public SkippableFactOnWindowsPowerShellAttribute()
+    {
+        if (PsesStdioLanguageServerProcessHost.IsWindowsPowerShell)
+        {
+            Skip = "Attach wedges during setup on Windows PowerShell since the 20260614 runner image; see https://github.com/PowerShell/PowerShellEditorServices/issues/2323.";
+        }
+    }
+}