test(e2e): deflake webhook redelivery target registration (#4848)

Register the webhook target while its endpoint is reachable, then drop
the listener before the PUT: registering against a dead endpoint stalls
behind the reachability probe timeout and flaked the ARN wait on the
rustfs#4821 merge run. Also widen the registration wait to 20s.

crates/e2e_test/src/notification_webhook_test.rs

@@ -308,7 +308,7 @@ async fn configure_webhook_target(env: &RustFSTestEnvironment, target_name: &str
 async fn wait_for_target_registered(env: &RustFSTestEnvironment, target_name: &str) -> TestResult {
     let suffix = format!(":{target_name}:webhook");
     let url = format!("{}/rustfs/admin/v3/target/arns", env.url);
-    for _ in 0..40 {
+    for _ in 0..80 {
         let response = signed_admin_request(env, http::Method::GET, &url, None).await?;
         if response.status() == StatusCode::OK {
             let arns: Vec<String> = serde_json::from_slice(&response.bytes().await?)?;
@@ -537,16 +537,28 @@ async fn test_webhook_redelivers_event_after_target_recovers() -> TestResult {
     let client = env.create_s3_client();
     client.create_bucket().bucket(bucket).send().await?;
 
-    // Reserve a port but leave it unbound: the webhook endpoint is
-    // unreachable (connection refused -> retryable NotConnected), so the first
-    // delivery attempts fail and the event is persisted to the queue store.
-    let port = RustFSTestEnvironment::find_available_port().await?;
+    // Configure the target while its endpoint is reachable so activation and
+    // ARN registration complete deterministically. Registering against a dead
+    // endpoint stalls behind the reachability probe's timeout and flakes the
+    // registration wait on loaded runners (observed on the merge run of
+    // rustfs#4821).
+    let listener = TcpListener::bind("0.0.0.0:0").await?;
+    let port = listener.local_addr()?.port();
     let endpoint_ip = local_ip()?;
     let endpoint = format!("http://{endpoint_ip}.nip.io:{port}/events");
+    let (setup_tx, _setup_rx) = mpsc::unbounded_channel();
+    let setup_handle = serve_event_collector(listener, setup_tx);
+
     configure_webhook_target(&env, target, &endpoint).await?;
     wait_for_target_registered(&env, target).await?;
     put_notification_config(&client, bucket, target, "uploads/", ".dat").await?;
 
+    // Take the endpoint down (drops the listener, so connections are refused —
+    // a retryable NotConnected), then PUT: the event cannot be delivered and
+    // must survive on the durable queue store.
+    setup_handle.abort();
+    let _ = setup_handle.await;
+
     let key = "uploads/redeliver.dat";
     client
         .put_object()
@@ -556,7 +568,12 @@ async fn test_webhook_redelivers_event_after_target_recovers() -> TestResult {
         .send()
         .await?;
 
-    // Bring the endpoint up on the reserved port; the replay worker retries with
+    // Hold the endpoint down long enough for at least one replay attempt to
+    // fail (the replay worker scans the store every 500ms), so recovery below
+    // exercises real redelivery rather than a first-attempt success.
+    tokio::time::sleep(Duration::from_secs(2)).await;
+
+    // Bring the endpoint back on the same port; the replay worker retries with
     // exponential backoff and delivers the queued event.
     let listener = TcpListener::bind(("0.0.0.0", port)).await?;
     let (tx, mut rx) = mpsc::unbounded_channel();