fix(ecstore): merge peer pool meta reload monotonically (#6392)

The peer reload_pool_meta handler blindly replaced in-memory pool
metadata with the persisted snapshot, so a delayed or out-of-order
reload could roll back newer local queued/canceled/failed/complete
decommission state, and a missing pool.bin wiped local state to an
empty default.

Route peer reload through the same monotonic merge used by the admin
status refresh (merge_pool_status_refresh): entries are replaced only
when strictly newer and no local worker is active; missing snapshots
fail closed. The helper now reports whether any entry was replaced or
appended, and rejected stale/missing reloads are logged. The RPC
handler spawns missing decommission workers only after a reload
actually merged newer state, so duplicate deliveries cannot start
workers for an older generation.

Fixes rustfs/backlog#1917

rustfs/src/storage/rpc/node_service.rs

@@ -1987,8 +1987,10 @@ impl Node for NodeService {
                 error_info: Some("errServerNotInitialized".to_string()),
             }));
         };
+        // Recover missing workers only after the reload merged newer state; a
+        // stale or duplicate reload must not spawn workers for an older generation.
         match store.reload_pool_meta().await {
-            Ok(_) => match store.spawn_missing_local_decommission_routines().await {
+            Ok(true) => match store.spawn_missing_local_decommission_routines().await {
                 Ok(_) => Ok(Response::new(ReloadPoolMetaResponse {
                     success: true,
                     error_info: None,
@@ -1998,6 +2000,10 @@ impl Node for NodeService {
                     error_info: Some(err.to_string()),
                 })),
             },
+            Ok(false) => Ok(Response::new(ReloadPoolMetaResponse {
+                success: true,
+                error_info: None,
+            })),
             Err(err) => Ok(Response::new(ReloadPoolMetaResponse {
                 success: false,
                 error_info: Some(err.to_string()),