Serialize references to errors in the error priority queue

It doesn't make sense to emit references to future values at higher pri
than the value that they're referencing.

This ensures that we don't emit hard forward references to values that
don't yet exist.

Author: sebmarkbage

packages/react-client/src/ReactFlightClient.js

@@ -312,6 +312,11 @@ export function parseModelString(
       } else {
         const id = parseInt(value.substring(1), 16);
         const chunk = getChunk(response, id);
+        if (chunk.status === PENDING) {
+          throw new Error(
+            "We didn't expect to see a forward reference. This is a bug in the React Server.",
+          );
+        }
         return readChunk(chunk);
       }
     }

packages/react-server/src/ReactFlightServer.js

@@ -902,7 +902,7 @@ function abortTask(task: Task, request: Request, errorId: number): void {
   // has a single value referencing the error.
   const ref = serializeByValueID(errorId);
   const processedChunk = processReferenceChunk(request, task.id, ref);
-  request.completedJSONChunks.push(processedChunk);
+  request.completedErrorChunks.push(processedChunk);
 }
 
 function flushCompletedChunks(