refactor: improve jumpToMessage code

i.e. ensure that `__internal_check_jump_to_message`
was set by this component instance prior to resetting it.

This doesn't appear to fix any current bugs,
but hopefully will save us later.

packages/frontend/src/components/message/MessageList.tsx

@@ -236,16 +236,27 @@ export default function MessageList({ accountId, chat, refComposer }: Props) {
   }
   maybeJumpToMessageHack()
   window.__internal_check_jump_to_message = maybeJumpToMessageHack
+  const thisMessageListIntanceSymbol = useRef(Symbol())
+  window.__internal_current_message_list_instance_id =
+    thisMessageListIntanceSymbol.current
   useEffect(() => {
-    // Unset this when unmounting, so that it's the next component instance
+    // Unset `__internal_check_jump_to_message` when unmounting,
+    // so that it's the next component instance
     // that handles the `__internal_jump_to_message_asap` value.
     // This is important e.g. for "Show in Chat" in the gallery.
     // The gallery is displayed when the MessageList component
     // is not displayed.
-    //
-    // TODO we probably need to ensure that the next component instance
-    // didn't already set it itself.
     return () => {
+      if (
+        window.__internal_current_message_list_instance_id !==
+        // eslint-disable-next-line react-hooks/exhaustive-deps
+        thisMessageListIntanceSymbol.current
+      ) {
+        // This means that another component has already set
+        // `__internal_check_jump_to_message`.
+        // No need to clean it up.
+        return
+      }
       window.__internal_check_jump_to_message = undefined
     }
   }, [])

packages/frontend/src/global.d.ts

@@ -65,6 +65,11 @@ declare global {
      * it gets assigned when the component gets rendered.
      */
     __internal_check_jump_to_message?: () => void
+    /**
+     * This is used by MessageList to see if another, newer instance
+     * of a MessageList exists.
+     */
+    __internal_current_message_list_instance_id?: symbol
     __updateAccountListSidebar: (() => void) | undefined
   }
 }