fix(messages): restore explicit responsePrefix default

docs/providers/whatsapp.md

@@ -59,8 +59,8 @@ When the wizard asks for your personal WhatsApp number, enter the phone you will
 }
 ```
 
-Tip: if you set the routed agent’s `identity.name`, you can omit
-`messages.responsePrefix` and it will default to `[{identity.name}]`.
+Tip: set `messages.responsePrefix` explicitly if you want a consistent bot prefix
+on outbound replies.
 
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 - **Local eSIM** from your country's mobile carrier (most reliable)