diff --git a/nestsClient/tests/hang-interop/hang-listen/src/main.rs b/nestsClient/tests/hang-interop/hang-listen/src/main.rs
index 2964cc712d..761335e5d2 100644
--- a/nestsClient/tests/hang-interop/hang-listen/src/main.rs
+++ b/nestsClient/tests/hang-interop/hang-listen/src/main.rs
@@ -165,6 +165,30 @@ async fn listen(
     let broadcast = broadcast.ok_or_else(|| anyhow!("broadcast unannounced: {path}"))?;
     tracing::info!(%path, "broadcast announced");
 
+    // Give the relay 250 ms to fully prime its per-broadcast
+    // upstream-subscribe pump before we subscribe. moq-rs 0.10.x's
+    // `Origin::announced()` returns as soon as the broadcast lands
+    // in the relay's origin map — which is BEFORE the relay's
+    // upstream subscribe-pump (the machinery that forwards a
+    // downstream listener's SUBSCRIBE to the speaker) is fully
+    // alive. Speaker-side stderr from a failing run shows the
+    // ANNOUNCE Please/Active handshake completes but no subsequent
+    // SUBSCRIBE inbound for the entire 10 s catalog-read window —
+    // the relay accepts the listener's SUBSCRIBE but silently
+    // drops it because the upstream pump isn't ready yet.
+    //
+    // The Kotlin↔Kotlin diagnostic test does NOT hit this race
+    // because its listener takes longer to set up (multiple
+    // session-level coroutines launched before the actual
+    // SUBSCRIBE), giving the relay's pump natural breathing room.
+    // Hang-listen's tighter pipeline reaches `subscribe_track`
+    // within microseconds of `announced()` returning, racing the
+    // relay's pump setup.
+    //
+    // 250 ms covers observed setup latency in sweep runs without
+    // measurably extending the suite wallclock.
+    tokio::time::sleep(Duration::from_millis(250)).await;
+
     // Subscribe to the catalog and read the first published
     // version. The naïve "subscribe → next() with timeout → on
     // timeout resubscribe" pattern is broken on moq-rs 0.10.x: