Get `mentions` from a chat message

Description

We need a way to Get mentions from a chat message.

Describe the solution you’d like

Add at_items property to the message returned by /chat/users/{userId}/messages/{messageId}.

Describe alternatives you’ve considered

Add at_items property to the event body of chat_message.* events.

Additional context

When we send message to a chat using API /chat/users/{userId}/messages we can add mentions using at_items property.

But when we get message by /chat/users/{userId}/messages/{messageId} or catch a chat_message.sent event using webhook we can’t get an array of mentions.

We need a way to get mentions from a chat message.