going back to what was working...

src/PSParallelPipeline/Commands/InvokeParallelCommand.cs

@@ -91,12 +91,12 @@ protected override void ProcessRecord()
         catch (Exception _) when (_ is PipelineStoppedException or FlowControlException)
         {
             _worker.Cancel();
-            _worker.Wait();
+            _worker.WaitOnCancel();
             throw;
         }
         catch (OperationCanceledException exception)
         {
-            _worker.Wait();
+            _worker.WaitOnCancel();
             exception.WriteTimeoutError(this);
         }
         catch (Exception exception)
@@ -121,12 +121,12 @@ protected override void EndProcessing()
         catch (Exception _) when (_ is PipelineStoppedException or FlowControlException)
         {
             _worker.Cancel();
-            _worker.Wait();
+            _worker.WaitOnCancel();
             throw;
         }
         catch (OperationCanceledException exception)
         {
-            _worker.Wait();
+            _worker.WaitOnCancel();
             exception.WriteTimeoutError(this);
         }
         catch (Exception exception)

src/PSParallelPipeline/RunspacePool.cs

@@ -69,6 +69,7 @@ private async Task<Runspace> GetRunspaceAsync()
         {
             return runspace;
         }
+
         return CreateRunspace();
     }
 

src/PSParallelPipeline/Worker.cs

@@ -37,6 +37,12 @@ internal Worker(PoolSettings settings)
 
     internal void Wait() => _worker?.Wait();
 
+    internal void WaitOnCancel() => _worker?
+        .ContinueWith(
+            _ => { _runspacePool.WaitOnCancel(); },
+            TaskContinuationOptions.NotOnRanToCompletion)
+        .Wait();
+
     internal void Cancel() => _cts.Cancel();
 
     internal void CancelAfter(TimeSpan span) => _cts.CancelAfter(span);
@@ -64,32 +70,24 @@ internal IEnumerable<PSOutputData> GetConsumingEnumerable() =>
 
     private async Task Start()
     {
-        try
+        while (!_inputQueue.IsCompleted)
         {
-            while (!_inputQueue.IsCompleted)
+            if (_inputQueue.TryTake(out PSTask ps, 0, Token))
             {
-                if (_inputQueue.TryTake(out PSTask ps, 0, Token))
-                {
-                    await _runspacePool.EnqueueAsync(ps);
-                }
+                await _runspacePool.EnqueueAsync(ps);
             }
-
-            await _runspacePool.ProcessAllAsync();
-            OutputPipe.CompleteAdding();
-        }
-        catch (OperationCanceledException)
-        {
-            _runspacePool.WaitOnCancel();
-            _runspacePool.Dispose();
         }
+
+        await _runspacePool.ProcessAllAsync();
+        OutputPipe.CompleteAdding();
     }
 
     public void Dispose()
     {
         _inputQueue.Dispose();
         OutputStreams.Dispose();
-        _runspacePool.Dispose();
         _cts.Dispose();
+        _runspacePool.Dispose();
         GC.SuppressFinalize(this);
     }
 }