diff --git a/packages/syntax-playground/src/echo-server-syndicate-js.js b/packages/syntax-playground/src/echo-server-syndicate-js.js
index 284204a..9f18755 100644
--- a/packages/syntax-playground/src/echo-server-syndicate-js.js
+++ b/packages/syntax-playground/src/echo-server-syndicate-js.js
@@ -1,10 +1,14 @@
 const S = activate require("@syndicate-lang/driver-streams-node");
 
+assertion type ConnectionActive();
+
 spawn named 'echoserver' {
   on asserted S.Stream($id, S.Incoming(S.TcpListener(5999))) {
     spawn {
+      assert ConnectionActive();
       stop on retracted S.Stream(id, S.Duplex());
       on message S.Stream(id, S.Data($bs)) send S.Stream(id, S.Push(bs, false));
     }
   }
+  stop on retracted ConnectionActive();
 }