Prevent initializing a realtime stream on a completed run

Author: ericallam

apps/webapp/app/routes/realtime.v1.streams.$runId.$target.$streamId.ts

@@ -68,9 +68,16 @@ const { action } = createActionApiRoute(
         },
         select: {
           realtimeStreamsVersion: true,
+          completedAt: true,
         },
       });
 
+      if (updatedRun.completedAt) {
+        return new Response("Cannot initialize a realtime stream on a completed run", {
+          status: 400,
+        });
+      }
+
       const realtimeStream = getRealtimeStreamInstance(
         authentication.environment,
         updatedRun.realtimeStreamsVersion