test: measure broken-output shutdown after readiness (Refs #529)

Establish a bounded info exchange before closing the same stdout pipe, so startup is not charged to the unchanged one-second shutdown deadline. Explicitly terminate and bounded-join the readiness helper on setup failure.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: karthiknadig

crates/pet/tests/jsonrpc_server_test.rs

@@ -585,7 +585,31 @@ fn truncated_input_exits_unsuccessfully_without_an_error_flood() {
 #[test]
 fn closed_output_exits_without_waiting_for_stdin_eof() {
     let mut fixture = ShutdownFixture::spawn();
-    drop(fixture.child.stdout.take());
+    let mut stdout = BufReader::new(fixture.child.stdout.take().unwrap());
+    let (sender, receiver) = mpsc::sync_channel(1);
+    let reader = thread::spawn(move || {
+        let response = jsonrpc_client::read_message(&mut stdout);
+        let _ = sender.send((stdout, response));
+    });
+    fixture.send(br#"{"jsonrpc":"2.0","id":"ready","method":"info"}"#);
+    let (stdout, response) = match receiver.recv_timeout(Duration::from_secs(10)) {
+        Ok(result) => result,
+        Err(error) => {
+            drop(receiver);
+            fixture.child.stdin.take();
+            let shutdown =
+                jsonrpc_client::shutdown_fixture(&mut fixture.child, Duration::from_secs(4));
+            let joined = jsonrpc_client::join_reader(reader, Duration::from_secs(4));
+            panic!("server readiness failed: {error}; shutdown: {shutdown:?}; reader: {joined:?}");
+        }
+    };
+    jsonrpc_client::join_reader(reader, Duration::from_secs(1)).unwrap();
+    let response = response
+        .unwrap()
+        .expect("ready server must respond to info");
+    assert_eq!(response["id"], "ready");
+    drop(stdout);
+
     let started = Instant::now();
     fixture.send(br#"{"jsonrpc":"2.0","id":1,"method":"info"}"#);
     let status = jsonrpc_client::wait_for_exit(&mut fixture.child, Duration::from_secs(1)).unwrap();