[Runtime Async] do not hold to continuation state when completing reusable valuetask sources

src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Sources/ManualResetValueTaskSourceCore.cs

@@ -221,28 +221,30 @@ private void SignalCompletion()
 
             if (continuation is not null)
             {
-                Debug.Assert(continuation is not null, $"{nameof(continuation)} is null");
-
+                object? state = _continuationState;
+                _continuationState = null;
                 object? context = _capturedContext;
+                _capturedContext = null;
+
                 if (context is null)
                 {
                     if (_runContinuationsAsynchronously)
                     {
-                        ThreadPool.UnsafeQueueUserWorkItem(continuation, _continuationState, preferLocal: true);
+                        ThreadPool.UnsafeQueueUserWorkItem(continuation, state, preferLocal: true);
                     }
                     else
                     {
-                        continuation(_continuationState);
+                        continuation(state);
                     }
                 }
                 else if (context is ExecutionContext or CapturedSchedulerAndExecutionContext)
                 {
-                    ManualResetValueTaskSourceCoreShared.InvokeContinuationWithContext(context, continuation, _continuationState, _runContinuationsAsynchronously);
+                    ManualResetValueTaskSourceCoreShared.InvokeContinuationWithContext(context, continuation, state, _runContinuationsAsynchronously);
                 }
                 else
                 {
                     Debug.Assert(context is TaskScheduler or SynchronizationContext, $"context is {context}");
-                    ManualResetValueTaskSourceCoreShared.ScheduleCapturedContext(context, continuation, _continuationState);
+                    ManualResetValueTaskSourceCoreShared.ScheduleCapturedContext(context, continuation, state);
                 }
             }
         }

src/libraries/System.Threading.Channels/src/System/Threading/Channels/AsyncOperation.cs

@@ -266,11 +266,14 @@ private void SetCompletionAndInvokeContinuation()
                 ctx as ExecutionContext ??
                 (ctx as CapturedSchedulerAndExecutionContext)?._executionContext;
 
+            _capturedContext = null;
             if (ec is null)
             {
                 Action<object?> c = _continuation!;
                 _continuation = s_completedSentinel;
-                c(_continuationState);
+                object? state = _continuationState;
+                _continuationState = null;
+                c(state);
             }
             else
             {
@@ -279,7 +282,9 @@ ctx as ExecutionContext ??
                     var thisRef = (AsyncOperation)s!;
                     Action<object?> c = thisRef._continuation!;
                     thisRef._continuation = s_completedSentinel;
-                    c(thisRef._continuationState);
+                    object? state = thisRef._continuationState;
+                    thisRef._continuationState = null;
+                    c(state);
                 }, this);
             }
         }