Set IsDebuggingRemoteRunspace sooner for attach (#1815)

Since we're not setting `DebugContext.IsActive` sooner, we also need to
set `IsDebuggingRemoteRunspace` early as well. Otherwise `DoOneRepl`
sees `IsActive`, but not in a breakpoint, and stops debugging.

Author: SeeminglyScience

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

@@ -216,6 +216,26 @@ public async Task<LaunchResponse> Handle(PsesLaunchRequestArguments request, Can
         }
 
         public async Task<AttachResponse> Handle(PsesAttachRequestArguments request, CancellationToken cancellationToken)
+        {
+            // We want to set this as early as possible to avoid an early `StopDebugging` call in
+            // DoOneRepl. There's too many places to reset this if it fails so we're wrapping the
+            // entire method in a try here to reset it if failed.
+            //
+            // TODO: Ideally DoOneRepl would be paused until the attach is fully initialized, though
+            //       the current architecture makes that challenging.
+            _debugService.IsDebuggingRemoteRunspace = true;
+            try
+            {
+                return await HandleImpl(request, cancellationToken).ConfigureAwait(false);
+            }
+            catch
+            {
+                _debugService.IsDebuggingRemoteRunspace = false;
+                throw;
+            }
+        }
+
+        private async Task<AttachResponse> HandleImpl(PsesAttachRequestArguments request, CancellationToken cancellationToken)
         {
             // The debugger has officially started. We use this to later check if we should stop it.
             ((PsesInternalHost)_executionService).DebugContext.IsActive = true;
@@ -413,7 +433,6 @@ await _executionService.ExecutePSCommandAsync(
             // Clear any existing breakpoints before proceeding
             await _breakpointService.RemoveAllBreakpointsAsync().ConfigureAwait(continueOnCapturedContext: false);
 
-            _debugService.IsDebuggingRemoteRunspace = true;
             _debugStateService.WaitingForAttach = true;
             Task nonAwaitedTask = _executionService
                 .ExecutePSCommandAsync(debugRunspaceCmd, CancellationToken.None, PowerShellExecutionOptions.ImmediateInteractive)