Update cluster-spec with Valkey 8.0 cluster improvements

Signed-off-by: Ping Xie <[email protected]>

topics/cluster-spec.md

@@ -479,6 +479,16 @@ is that:
 * All queries about existing keys are processed by "A".
 * All queries about non-existing keys in A are processed by "B", because "A" will redirect clients to "B".
 
+Starting from Valkey 8.0, the `CLUSTER SETSLOT` command is synchronously replicated to all healthy replicas
+running Valkey version 8.0+. By default, this synchronous replication must complete within 2 seconds.
+If the replication fails, the primary does not execute the command, and the client receives a
+`NOREPLICAS Not enough good replicas to write` error. Operators can retry the command or customize the
+timeout using the `TIMEOUT` parameter to further increase the reliability of live reconfiguration:
+
+    CLUSTER SETSLOT slot [MIGRATING|IMPORTING|NODE] node-id [TIMEOUT timeout]
+
+Here, `timeout` is measured in seconds, with 0 meaning to wait indefinitely.
+
 This way we no longer create new keys in "A".
 In the meantime, `valkey-cli` used during reshardings
 and Valkey Cluster configuration will migrate existing keys in
@@ -513,6 +523,11 @@ set the slots to their normal state again. The same command is usually
 sent to all other nodes to avoid waiting for the natural
 propagation of the new configuration across the cluster.
 
+Starting from Valkey 8.0, Valkey clusters introduce the ability to elect a primary in empty shards.
+This behavior ensures that even when a shard is in the process of receiving its first slot,
+a primary can be elected. This prevents scenarios where there would be no primary available in the
+empty shard to handle redirected requests from the official slot owner,
+thereby maintaining availability during the live reconfiguration.
 ### ASK redirection
 
 In the previous section, we briefly talked about ASK redirection. Why can't
@@ -550,6 +565,11 @@ Slots migration is explained in similar terms but with different wording
 (for the sake of redundancy in the documentation) in the `CLUSTER SETSLOT`
 command documentation.
 
+Starting from Valkey 8.0, when the primary in either the source or target shard fails during live reconfiguration,
+the primary in the other shard will automatically attempt to update its migrating/importing state to correctly pair
+with the newly elected primary. If this update is successful, the ASK redirection will continue functioning without
+requiring operator intervention.
+
 ### Client connections and redirection handling
 
 To be efficient, Valkey Cluster clients maintain a map of the current slot