Harden decommission checks for BlobDepot (#28216)

Author: alexvru

ydb/core/blobstorage/nodewarden/node_warden_group.cpp

@@ -115,9 +115,14 @@ namespace NKikimr::NStorage {
         TGroupRecord& group = it->second;
         group.MaxKnownGeneration = Max(group.MaxKnownGeneration, generation);
         if (newGroup) {
-            const auto erasure = static_cast<TBlobStorageGroupType::EErasureSpecies>(newGroup->GetErasureSpecies());
-            Y_DEBUG_ABORT_UNLESS(!group.GType || group.GType->GetErasure() == erasure);
-            group.GType.emplace(erasure);
+            if (newGroup->HasErasureSpecies()) {
+                const auto erasure = static_cast<TBlobStorageGroupType::EErasureSpecies>(newGroup->GetErasureSpecies());
+                Y_DEBUG_ABORT_UNLESS(!group.GType || group.GType->GetErasure() == erasure);
+                group.GType.emplace(erasure);
+            } else {
+                Y_ABORT_UNLESS(newGroup->RingsSize() == 0); // ensure no VDisks in group
+                group.GType.emplace(TBlobStorageGroupType::ErasureNone);
+            }
         }
 
         // forget pending queries