fix(scanner): recover usage floor from fenced backups

Co-Authored-By: heihutu <heihutu@gmail.com>

crates/scanner/src/scanner/cycle_state.rs

@@ -1393,7 +1393,6 @@ pub(super) async fn persisted_usage_floor_for_startup(
                     // This is still persisted state, so it must not enable a
                     // missing-state bootstrap.  Continue to a legacy pair in
                     // case it contains a complete, fenced snapshot.
-                    any_found = false;
                 } else {
                     let backup_epoch = usage.scanner_epoch.unwrap_or_default();
                     // A backup write from an older leader may complete after the

crates/scanner/src/scanner/tests.rs

@@ -1923,6 +1923,38 @@ async fn scanner_startup_uses_primary_and_backup_usage_floor() {
     assert_eq!(epoch, 11);
 }
 
+#[tokio::test]
+async fn scanner_usage_floor_keeps_valid_primary_when_backup_has_no_identity() {
+    let store = Arc::new(MemoryConfigStore::default());
+    let backup_path = format!("{}.bkp", DATA_USAGE_OBJ_NAME_PATH.as_str());
+    let mut primary = complete_usage_with_bucket_count(Some(std::time::SystemTime::UNIX_EPOCH), 0);
+    primary.scanner_epoch = Some(8);
+    primary.scanner_cycle = Some(100);
+    let backup = DataUsageInfo {
+        scanner_epoch: Some(9),
+        scanner_cycle: Some(101),
+        usage_snapshot_complete: false,
+        ..Default::default()
+    };
+
+    for (path, usage) in [(DATA_USAGE_OBJ_NAME_PATH.as_str(), primary), (backup_path.as_str(), backup)] {
+        store.objects.lock().await.insert(
+            memory_config_key(RUSTFS_META_BUCKET, path),
+            serde_json::to_vec(&usage).expect("usage snapshot should encode"),
+        );
+    }
+
+    assert_eq!(
+        persisted_usage_floor(store)
+            .await
+            .expect("valid primary should remain authoritative"),
+        PersistedUsageFloor {
+            next_cycle: 101,
+            leader_epoch: 8,
+        }
+    );
+}
+
 #[tokio::test]
 async fn scanner_usage_floor_recovers_from_incomplete_v2_primary_using_fenced_backup() {
     let store = Arc::new(MemoryConfigStore::default());