Docs: clarify auto_ddl behaviour during ZODAN node addition.

Author: Ibrar Ahmed

docs/modify/zodan/zodan_readme.md

@@ -36,6 +36,18 @@ After adding the new node, you can use health checks on your cluster to ensure t
 - Python 3
 - Passwordless access or a properly configured `.pgpass` file for remote connections
 
+!!! Warning "DDL and auto_ddl during node addition"
+
+    **Recommended:** Disable `auto_ddl` (`spock.enable_ddl_replication = off`) on
+    all cluster nodes before running ZODAN and re-enable it after the new node is
+    fully subscribed.
+
+    ZODAN can run with `auto_ddl` enabled, but you must avoid any DDL activity
+    during the operation.  Do not run burst DDL (many statements in rapid
+    succession), heavy schema migrations, or DDL inside transactions while ZODAN
+    is active.  Concurrent DDL can cause replication conflicts or leave the new
+    node with an inconsistent schema.
+
 **Running a Health Check**
 
 Invoke the script on the node you are validating:

docs/modify/zodan/zodan_tutorial.md

@@ -7,7 +7,15 @@ In this detailed walk through, we'll add a fourth node to a three-node cluster w
     **Important Prerequisites and Warnings**
 
         - The new node should not be accessible to users while adding the node.
-        - Disable `auto_ddl` on all cluster nodes.
+        - **Recommended:** Disable `auto_ddl` (`spock.enable_ddl_replication = off`)
+          on all cluster nodes before adding a new node and re-enable it after the
+          process completes.  This is the safest approach.
+        - If you must leave `auto_ddl` enabled, exercise caution: avoid any DDL
+          changes during the node addition window.  In particular, do not run burst
+          DDL (many statements in rapid succession), heavy schema migrations, or
+          DDL inside transactions while ZODAN is running.  Concurrent DDL with an
+          active ZODAN operation can cause replication conflicts or an inconsistent
+          schema on the new node.
         - Do not modify your DDL during node addition.
         - The users must be identical on the source and target node. You must create any users on the target node before proceeding; the permissions must be *identical* for all users on both the source and target nodes.