Scroll to bottom of conversation when message is sent

ts/components/conversation/Timeline.tsx

@@ -594,7 +594,14 @@ export class Timeline extends React.Component<
       }
     }
 
-    if (oldItems.length !== newItems.length) {
+    // We know that all items will be in order and that items can only be added at either
+    // end, so we can check for equality without checking each item in the array
+    const haveItemsChanged =
+      oldItems.length !== newItems.length ||
+      oldItems.at(0) !== newItems.at(0) ||
+      oldItems.at(-1) !== newItems.at(-1);
+
+    if (haveItemsChanged) {
       this.updateIntersectionObserver();
 
       // This condition is somewhat arbitrary.

ts/models/conversations.ts

@@ -1436,7 +1436,10 @@ export class ConversationModel extends window.Backbone
       newestId && messageIds && messageIds[messageIds.length - 1] === newestId;
 
     if (isJustSent && existingConversation && !isLatestInMemory) {
-      void this.loadNewestMessages(undefined, undefined);
+      // The message is being sent before the user has scrolled down to load the newest
+      // messages into memory; in that case, we scroll the user all the way down by
+      // loading the newest message
+      drop(this.loadNewestMessages(newestId, undefined));
     } else if (
       // The message has to be not a story or has to be a story reply in direct
       // conversation.