Wait for busy guest readiness before measuring shutdown grace

cli/tests/host/core.rs

@@ -1015,6 +1015,7 @@ async fn stop_deadlines() {
 async fn shutdown_stops_busy_processes_in_parallel_after_five_seconds() {
     let w = TestWorld::new();
     let h = w.start().await;
+    let mut notifications = h.subscribe();
 
     let mut tasks = Vec::new();
     for _ in 0..2 {
@@ -1024,14 +1025,14 @@ async fn shutdown_stops_busy_processes_in_parallel_after_five_seconds() {
         }));
     }
     tokio::time::timeout(std::time::Duration::from_secs(20), async {
-        while h
-            .processes()
-            .values()
-            .filter(|p| p.plugin == "probe" && p.method == "busy")
-            .count()
-            != 2
-        {
-            tokio::task::yield_now().await;
+        // Admission precedes guest startup. Stopping at admission can close
+        // stdin before the guest receives its busy request, so there is then
+        // no busy work that needs the five-second kill budget.
+        let mut ready = 0;
+        while ready != tasks.len() {
+            if notifications.recv().await.unwrap()["params"]["name"] == "busy-ready" {
+                ready += 1;
+            }
         }
     })
     .await