fix(replication): preserve ordered tag deletions

Persist, send and reconcile empty tag states together with their revision
across COPY, PUT and multipart replication. Advance local tag mutations
under the existing locks and preserve current tags during replication ACK.

Cover signed HTTP, persistent single/multiple pool state, KMS, SSE-C key
rotation, ordering, retry and duplicate requests. Record real Opus plan
consensus, implementation review and local verification evidence.

Signed-off-by: Feng Ruohang <rh@vonng.com>
(cherry picked from commit 115fe8b12329d147adbaf817faa1737392ecbf9b)
Signed-off-by: Feng Ruohang <rh@vonng.com>

cmd/erasure-server-pool-consistency.go

@@ -242,6 +242,21 @@ func reconcileStoredObjectTags(metadata map[string]string, storedTags, storedTim
 	}
 }
 
+// Local tagging mutations must advance the revision they overwrite, even when
+// a request's clock or lock acquisition order is behind the stored revision.
+// Replica writes use reconcileStoredObjectTags instead of minting a revision.
+func monotonicTaggingTimestamp(incoming, stored string) string {
+	requested, err := time.Parse(time.RFC3339Nano, incoming)
+	if err != nil {
+		return incoming
+	}
+	current, err := time.Parse(time.RFC3339Nano, stored)
+	if err != nil || requested.After(current) {
+		return incoming
+	}
+	return current.Add(time.Nanosecond).UTC().Format(time.RFC3339Nano)
+}
+
 // A restored version still owns its tier reference even while IsRemote is
 // false. Only the last copy of a reference may schedule its contents for GC.
 func sharesTierObject(oi ObjectInfo, copies []PoolObjInfo) bool {