refactor(obs): migrate metrics runtime/schema and tighten migration guards (#2584)

crates/notify/src/global.rs

@@ -12,7 +12,10 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use crate::{BucketNotificationConfig, Event, EventArgs, LifecycleError, NotificationError, NotificationSystem};
+use crate::{
+    BucketNotificationConfig, Event, EventArgs, LifecycleError, NotificationError, NotificationMetricSnapshot,
+    NotificationSystem, NotificationTargetMetricSnapshot,
+};
 use rustfs_ecstore::config::Config;
 use rustfs_s3_common::EventName;
 use rustfs_targets::arn::TargetID;
@@ -41,6 +44,23 @@ pub fn notification_system() -> Option<Arc<NotificationSystem>> {
     NOTIFICATION_SYSTEM.get().cloned()
 }
 
+/// Returns aggregate notification delivery metrics for Prometheus collection.
+pub fn notification_metrics_snapshot() -> NotificationMetricSnapshot {
+    NOTIFICATION_SYSTEM
+        .get()
+        .map(|system| system.snapshot_metrics())
+        .unwrap_or_default()
+}
+
+/// Returns per-target notification delivery metrics for Prometheus collection.
+pub async fn notification_target_metrics() -> Vec<NotificationTargetMetricSnapshot> {
+    if let Some(system) = notification_system() {
+        system.snapshot_target_metrics().await
+    } else {
+        Vec::new()
+    }
+}
+
 /// Check if the notification system has been initialized.
 pub fn is_notification_system_initialized() -> bool {
     NOTIFICATION_SYSTEM.get().is_some()