Appends: note about append on a new attachment, remove note about continuous history not being supported yet

Author: SimonWoolf

src/pages/docs/messages/annotations.mdx

@@ -23,8 +23,6 @@ Annotations can be enabled for a channel or channel namespace with the *Message
 
 <Aside data-type='important'>
 When message annotations are enabled, messages are [persisted](/docs/storage-history/storage#all-message-persistence) regardless of whether or not persistence is enabled, in order to support the feature. This may increase your usage since [we charge for persisting messages](https://faqs.ably.com/how-does-ably-count-messages).
-
-[Continuous history](/docs/storage-history/history#continuous-history) features are not supported. Be aware that if you are currently using continuous history and enable annotations, updates, deletes, and appends, continuous history will no longer function.
 </Aside>
 
 1. Go to the **Settings** tab of an app in your dashboard.

src/pages/docs/messages/updates-deletes.mdx

@@ -27,8 +27,6 @@ Message updates and deletes can be enabled for a channel or channel namespace wi
 
 <Aside data-type='important'>
 When message updates and deletes are enabled, messages are [persisted](/docs/storage-history/storage#all-message-persistence) regardless of whether or not persistence is enabled, in order to support the feature. This may increase your usage since [we charge for persisting messages](https://faqs.ably.com/how-does-ably-count-messages).
-
-[Continuous history](/docs/storage-history/history#continuous-history) features are not yet supported. Be aware that for now, if you are currently using continuous history and enable annotations, updates, deletes, and appends, continuous history will no longer function.
 </Aside>
 
 1. Go to the **Settings** tab of an app in your dashboard.
@@ -411,6 +409,8 @@ If you are publishing appends at a high rate, use a [Realtime](/docs/api/realtim
 
 When Ably receives an append, it concatenates the provided data with the current latest version to calculate a full (non-incremental) version of the message. That version (with an action of `message.update`) is then used in contexts like [History](/docs/storage-history/history) and [rewind](/docs/channels/options/rewind), so that when using those APIs, you will always receive complete messages without needing to do any concatenation yourself, and can specify e.g. `rewind=10` to get the most recent 10 full, distinct messages.
 
+The first append you receive for a given message on an attachment is delivered as a fully-aggregated `message.update`, so that you don't need to reach into history to discover the full prior state of the message. You can then just concatenate the payloads of any subsequent `message.append`s for that message onto that first one to get the full payload. Note that Ably may at any time deliver an append as a `message.update` with the full rolled-up payload, so you should always check the `action` field to know whether to concatenate onto the existing payload or replace it.
+
 ### Comparison with update
 
 | Aspect | `updateMessage()` | `appendMessage()` |