perf(desktop): memoise MessageActionBar, stabilise its onRemindLater callback

Finding [L4] MessageActionBar (Tier 3): the action bar re-rendered with every
row render even when its props were unchanged. Wrap it in `React.memo`. The
memo was dead on arrival, though — the row passed an inline `onRemindLater`
arrow, a fresh function identity every render that defeated the shallow prop
compare. Extract it to a `handleRemindLater` useCallback (deps
[channelId, openReminder]); all other props are already stable (openReminder
and handleReactionSelect are useCallbacks, setBadgeBurstEmoji is a state
setter), so the memo now actually skips.

Co-authored-by: Tyler Longwell <tlongwell@block.xyz>
Signed-off-by: Tyler Longwell <tlongwell@block.xyz>

desktop/src/features/messages/ui/MessageActionBar.tsx

@@ -326,7 +326,7 @@ function isCustomEmojiShortcode(emoji: string) {
   return emoji.startsWith(":") && emoji.endsWith(":");
 }
 
-export function MessageActionBar({
+export const MessageActionBar = React.memo(function MessageActionBar({
   channelId,
   message,
   onDelete,
@@ -549,4 +549,6 @@ export function MessageActionBar({
       </div>
     </div>
   );
-}
+});
+
+MessageActionBar.displayName = "MessageActionBar";

desktop/src/features/messages/ui/MessageRow.tsx

@@ -153,6 +153,17 @@ export const MessageRow = React.memo(
     } = useReactionHandler(message, onToggleReaction);
     const { openReminder, activeReminderEventIds } = useRemindLater();
     const hasActiveReminder = activeReminderEventIds.has(message.id);
+    const handleRemindLater = React.useCallback(
+      (msg: TimelineMessage) => {
+        openReminder({
+          eventId: msg.id,
+          channelId: channelId ?? "",
+          preview: msg.body.slice(0, 100),
+          authorPubkey: msg.pubkey ?? "",
+        });
+      },
+      [channelId, openReminder],
+    );
     const mentionNames = React.useMemo(
       () => resolveMentionNames(message.tags, profiles),
       [profiles, message.tags],
@@ -446,14 +457,7 @@ export const MessageRow = React.memo(
           onReactionSelect={
             canToggleReactions ? handleReactionSelect : undefined
           }
-          onRemindLater={(msg) => {
-            openReminder({
-              eventId: msg.id,
-              channelId: channelId ?? "",
-              preview: msg.body.slice(0, 100),
-              authorPubkey: msg.pubkey ?? "",
-            });
-          }}
+          onRemindLater={handleRemindLater}
           onReply={onReply}
           onUnfollowThread={onUnfollowThread}
           reactionErrorMessage={reactionErrorMessage}