test(mqtt): drive per-node snapshots in discovery integration tests — #898

After the per-node discovery change, discovery configs are published the
first time a snapshot for a node_id arrives (not eagerly at startup). The
two discovery integration tests (discovery_topics_appear_on_broker,
privacy_mode_suppresses_biometric_discovery) spawned the publisher with an
empty broadcast channel and never sent a snapshot, so they collected []
and failed ("missing presence discovery topic in []").

Drive snapshots for the test node_id throughout the capture window (same
pattern as state_messages_published_on_snapshot_broadcast) so the per-node
device's discovery lands. Verified against a local mosquitto: 3 passed.

v2/crates/wifi-densepose-sensing-server/tests/mqtt_integration.rs

@@ -171,12 +171,28 @@ async fn discovery_topics_appear_on_broker() {
     // Spawn the publisher.
     let cfg = make_cfg(port, false, "discovery");
     let builder = make_builder("inttest1");
-    let (_tx, rx) = broadcast::channel::<VitalsSnapshot>(32);
+    let (tx, rx) = broadcast::channel::<VitalsSnapshot>(32);
     let _handle = spawn(cfg, builder, rx);
 
+    // #898: discovery is now published per-node the first time a snapshot for
+    // that node_id arrives (not eagerly at startup). Drive snapshots for
+    // "inttest1" throughout the window so its device's discovery lands — same
+    // pattern as state_messages_published_on_snapshot_broadcast.
+    let tx_bg = tx.clone();
+    let drive = tokio::spawn(async move {
+        for _ in 0..60 {
+            let _ = tx_bg.send(VitalsSnapshot {
+                node_id: "inttest1".into(),
+                ..Default::default()
+            });
+            tokio::time::sleep(Duration::from_millis(200)).await;
+        }
+    });
+
     // Drain the subscriber for up to 6 s — enough for initial discovery
     // + first availability publication.
     let msgs = collect_published(&mut sub_loop, Duration::from_secs(6)).await;
+    drive.abort();
     let _ = sub.disconnect().await;
 
     // Assertions: at least the presence + heart_rate + fall discovery
@@ -221,10 +237,23 @@ async fn privacy_mode_suppresses_biometric_discovery() {
 
     let cfg = make_cfg(port, /* privacy_mode = */ true, "privacy");
     let builder = make_builder("inttest2");
-    let (_tx, rx) = broadcast::channel::<VitalsSnapshot>(32);
+    let (tx, rx) = broadcast::channel::<VitalsSnapshot>(32);
     let _handle = spawn(cfg, builder, rx);
 
+    // #898: per-node discovery is triggered by a snapshot for that node_id.
+    let tx_bg = tx.clone();
+    let drive = tokio::spawn(async move {
+        for _ in 0..60 {
+            let _ = tx_bg.send(VitalsSnapshot {
+                node_id: "inttest2".into(),
+                ..Default::default()
+            });
+            tokio::time::sleep(Duration::from_millis(200)).await;
+        }
+    });
+
     let msgs = collect_published(&mut sub_loop, Duration::from_secs(6)).await;
+    drive.abort();
     let _ = sub.disconnect().await;
 
     let topics: Vec<&str> = msgs.iter().map(|(t, _, _)| t.as_str()).collect();