Fix flaky CanRegisterAndInvokeCommandWithScriptBlock on PS 5.1 / net462 (#2307)

* Initial plan

* Fix CanRegisterAndInvokeCommandWithScriptBlock test reliability on PS 5.1

The test was asserting on $global:extensionValue after invoking a script
block command via Invoke-Command. In Windows PowerShell 5.1 / net462, the
global variable set inside the script block is not reliably visible in
subsequent command invocations, causing the test to fail intermittently.

Replace the global-variable assertion with a scope-independent check:
change the script block to Write-Output 10 and verify only that registration
completes successfully (via the CommandAdded event) and invocation completes
without error. The behavior being tested (script-block-backed commands can
be registered and invoked) is still fully covered."

* Restore value assertion in CanRegisterAndInvokeCommandWithScriptBlock

Instead of passing ScriptBlock.Create() from C#, register the command
using AddScript so the script block is created in PowerShell's own
session state. ScriptBlock.Create() binds to the C# module context,
causing $global: writes via Invoke-Command to land in an isolated scope
on PS 5.1, making the value invisible to subsequent commands.

With the script block created in PS session state, the $global:extensionValue
assertion is reliable across all supported frameworks and is restored.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

Author: Copilot

test/PowerShellEditorServices.Test/Extensions/ExtensionCommandTests.cs

@@ -93,23 +93,24 @@ public async Task CanRegisterAndInvokeCommandWithScriptBlock()
             const string commandName = "test.scriptblock";
             const string commandDisplayName = "ScriptBlock extension";
 
+            // Use AddScript so the script block is created in PowerShell's own session state
+            // rather than C#'s module context. ScriptBlock.Create() binds to the C# module,
+            // so $global: writes made via Invoke-Command land in an isolated scope on PS 5.1.
             await psesHost.ExecutePSCommandAsync(
                 new PSCommand()
-                    .AddCommand("Register-EditorCommand")
-                    .AddParameter("Name", commandName)
-                    .AddParameter("DisplayName", commandDisplayName)
-                    .AddParameter("ScriptBlock", ScriptBlock.Create("$global:extensionValue = 10")),
+                    .AddScript(
+                        $"Register-EditorCommand -Name '{commandName}' -DisplayName \"{commandDisplayName}\" " +
+                        "-ScriptBlock { $global:extensionValue = 10 }"),
                 CancellationToken.None);
 
             Assert.NotNull(commandAdded);
             Assert.Equal(commandName, commandAdded.Name);
             Assert.Equal(commandDisplayName, commandAdded.DisplayName);
 
             // Invoke the command.
-            // TODO: What task was this cancelling?
-            await extensionCommandService.InvokeCommandAsync("test.scriptblock", editorContext);
+            await extensionCommandService.InvokeCommandAsync(commandName, editorContext);
 
-            // Assert the expected value
+            // Assert the expected value.
             PSCommand psCommand = new PSCommand().AddScript("$global:extensionValue");
             IEnumerable<int> results = await psesHost.ExecutePSCommandAsync<int>(psCommand, CancellationToken.None);
             Assert.Equal(10, results.FirstOrDefault());