docs: clear up default message persistence behavior for chat rooms

src/pages/docs/chat/rooms/history.mdx

@@ -3,7 +3,7 @@ title: Message storage and history
 meta_description: "Retrieve previously sent messages from history."
 ---
 
-The history feature enables users to retrieve messages that have been previously sent in a room. Ably stores chat messages for 30 days by default. You can extend this up to 365 days by [contacting us](https://ably.com/support).
+The history feature enables users to retrieve messages that have been previously sent in a room. [Message persistence](/docs/chat/rooms#persistence) is enabled by default for all chat rooms, with messages stored for 30 days. You can extend this retention period up to 365 days by [contacting us](https://ably.com/support).
 
 ## Retrieve previously sent messages <a id="history"/>
 

src/pages/docs/chat/rooms/index.mdx

@@ -11,6 +11,14 @@ It is important to note that each room is backed by a single Ably Pub/Sub channe
 
 The channel name is the same as the room name with an appended suffix of `::$chat` (e.g `some-room-id::$chat`). In most cases, you will not need to worry about this, as the Chat SDK handles the channel creation and management for you and capabilities can be configured at the room level.
 
+### Message persistence <a id="persistence"/>
+
+The `::$chat` suffix applied to chat room channels enables intrinsic default behaviors that differ from standard Pub/Sub channels. One of the most important behaviors is message persistence.
+
+Chat room channels have persistence enabled by default with a retention period of 30 days. This ensures that messages are automatically stored and can be retrieved using the [history feature](/docs/chat/rooms/history).
+
+The default 30-day retention period can be extended up to 365 days by [contacting us](https://ably.com/support). This automatic persistence is essential for supporting features such as [message updates](/docs/chat/rooms/messages#update), [message deletions](/docs/chat/rooms/messages#delete), and [message reactions](/docs/chat/rooms/message-reactions), all of which require access to previously sent messages.
+
 ## Use a room <a id="create"/>
 
 Users send messages to a room and subscribe to the room in order to receive messages.

src/pages/docs/chat/rooms/messages.mdx

@@ -7,6 +7,10 @@ Send, update, delete, and receive messages in a chat room with any number of par
 
 A user can also update or delete a message, all users that are subscribed to the room will be notified of the changes.
 
+<Aside data-type='note'>
+  To support updates, deletions, and [reactions](/docs/chat/rooms/message-reactions), [message persistence](/docs/chat/rooms#persistence) is enabled by default for all chat rooms.
+</Aside>
+
 ## Subscribe to messages <a id="subscribe"/>
 
 <If lang="javascript,swift,kotlin">