Fix ThreadsHandler to use singular pipeline thread

Author: rjmholt

src/PowerShellEditorServices/Services/DebugAdapter/Handlers/ThreadsHandler.cs

@@ -7,17 +7,26 @@
 using System.Threading.Tasks;
 using OmniSharp.Extensions.DebugAdapter.Protocol.Models;
 using OmniSharp.Extensions.DebugAdapter.Protocol.Requests;
+using Thread = OmniSharp.Extensions.DebugAdapter.Protocol.Models.Thread;
 
 namespace Microsoft.PowerShell.EditorServices.Handlers
 {
     internal class ThreadsHandler : IThreadsHandler
     {
+        internal static Thread PipelineThread { get; } =
+            new Thread { Id = 1, Name = "PowerShell Pipeline Thread" };
+
         public Task<ThreadsResponse> Handle(ThreadsArguments request, CancellationToken cancellationToken)
         {
             return Task.FromResult(new ThreadsResponse
             {
-                // TODO: This is an empty container of threads...do we need to make a thread?
-                Threads = new Container<System.Threading.Thread>()
+                // TODO: OmniSharp supports multithreaded debugging (where
+                // multiple threads can be debugged at once), but we don't. This
+                // means we always need to set AllThreadsStoppped and
+                // AllThreadsContinued in our events. But if we one day support
+                // multithreaded debugging, we'd need a way to associate
+                // debugged runspaces with .NET threads in a consistent way.
+                Threads = new Container<Thread>(PipelineThread)
             });
         }
     }