fix(native/community): derive heart state from props + store-optimistic delta

Replaces the previous mirrored localCount / localLike useState with derived
values computed from `post.likesCount` / `post.userLike` plus the existing
optimisticLikes entry from the community store. The local-state mirror was
the root cause of two separate bugs:

1. Foreign likes never reflected — useState seeded once from props on mount,
   so the React-Query cache patch in useCommunityRealtime updated the prop
   but the displayed count stayed frozen at the mount value.
2. The earlier sync-via-useEffect attempt (4c4792c, reverted in ab9472b)
   broke own-likes because clearing optimistic state could happen before
   the cache patch landed, so useEffect re-read a stale `post.likesCount`
   and snapped the count back down — visible as a 2 → 1 → 2 flicker on tap,
   and as the heart staying red after a toggle-off.

The fix is to NOT mirror at all. The store's `optimisticLikes` map already
stores `{ delta, userLike }` per post (it was set but never read before).
Render path now:
  displayedLike  = optimistic?.userLike  ?? (post.userLike === 'like' ? 'like' : null)
  displayedCount = (post.likesCount ?? 0) + (optimistic?.delta ?? 0)

In handleLike, after the API responds, the React-Query cache is patched
synchronously with the server-truth response before clearOptimisticLike
runs — so the moment the delta drops to 0, the prop already reflects the
new count. No race window, no useEffect, no own/foreign distinction needed.

`isLiking` is still kept as a re-tap guard against double-tap-mid-flight.

apps/rebreak-native/components/PostCard.tsx

@@ -26,8 +26,20 @@ function PostCardImpl({ post, onCommentPress }: Props) {
   const revertOptimisticLike = useCommunityStore((s) => s.revertOptimisticLike);
   const clearOptimisticLike = useCommunityStore((s) => s.clearOptimisticLike);
 
-  const [localLike, setLocalLike] = useState<'like' | null>(post.userLike === 'like' ? 'like' : null);
+  // Display state is DERIVED from props + the store-level optimistic delta.
-  const [localCount, setLocalCount] = useState(post.likesCount);
+  // No useState mirror — that's exactly what created the foreign-likes-don't-
+  // update bug (seed-once from props) and the post-action flicker (useEffect
+  // re-sync racing with the React-Query cache patch). Realtime patches the
+  // cache → prop changes → we re-render automatically. Optimistic UI lives
+  // for the ms between tap and API-response in the community-store's
+  // `optimisticLikes` map (delta + userLike).
+  const optimistic = useCommunityStore((s) => s.optimisticLikes[post.id]);
+  const displayedLike: 'like' | null = optimistic
+    ? optimistic.userLike
+    : post.userLike === 'like'
+      ? 'like'
+      : null;
+  const displayedCount = (post.likesCount ?? 0) + (optimistic?.delta ?? 0);
   const [isLiking, setIsLiking] = useState(false);
 
   // Heart-Pop Animation — Insta-Style: quick scale-up + spring-bounce back
@@ -136,9 +148,7 @@ function PostCardImpl({ post, onCommentPress }: Props) {
   const handleLike = useCallback(async () => {
     if (isLiking) return;
     triggerHeartPop();
-    const { newLike, newCount } = applyOptimisticLike(post.id, localLike, localCount);
+    applyOptimisticLike(post.id, displayedLike, displayedCount);
-    setLocalLike(newLike);
-    setLocalCount(newCount);
     setIsLiking(true);
     try {
       const res = await apiFetch<{
@@ -149,19 +159,29 @@ function PostCardImpl({ post, onCommentPress }: Props) {
         method: 'POST',
         body: { postId: post.id, type: 'like' },
       });
-      setLocalCount(res.likesCount);
+      // Patch the React-Query cache synchronously with server truth so the
-      setLocalLike(res.userLike === 'like' ? 'like' : null);
+      // prop reflects it BEFORE we clear the optimistic delta. Without this,
+      // there'd be a millisecond window between clearOptimistic (delta → 0)
+      // and the Realtime broadcast patching the cache — during which the
+      // displayed count would briefly snap back to the old prop value.
+      queryClient.setQueriesData<CommunityPost[]>(
+        { queryKey: ['community-posts'] },
+        (data) =>
+          Array.isArray(data)
+            ? data.map((p) =>
+                p.id === post.id
+                  ? { ...p, likesCount: res.likesCount, dislikesCount: res.dislikesCount, userLike: res.userLike }
+                  : p,
+              )
+            : data,
+      );
       clearOptimisticLike(post.id);
-      // KEIN queryClient.invalidateQueries — würde die komplette Liste neu laden,
-      // PostCard remounted, Heart-Pop-Animation abgebrochen. Local-State reicht.
     } catch {
       revertOptimisticLike(post.id);
-      setLocalLike(post.userLike === 'like' ? 'like' : null);
-      setLocalCount(post.likesCount);
     } finally {
       setIsLiking(false);
     }
-  }, [isLiking, localLike, localCount, post.id, post.userLike, post.likesCount, applyOptimisticLike, clearOptimisticLike, revertOptimisticLike, queryClient, triggerHeartPop]);
+  }, [isLiking, displayedLike, displayedCount, post.id, applyOptimisticLike, clearOptimisticLike, revertOptimisticLike, queryClient, triggerHeartPop]);
 
   return (
     <View style={{ backgroundColor: colors.bg, borderWidth: 1, borderColor: colors.border, borderRadius: 16, padding: 12, marginBottom: 12 }}>
@@ -278,13 +298,13 @@ function PostCardImpl({ post, onCommentPress }: Props) {
           >
             <Animated.View style={{ transform: [{ scale: heartScale }] }}>
               <Ionicons
-                name={localLike === 'like' ? 'heart' : 'heart-outline'}
+                name={displayedLike === 'like' ? 'heart' : 'heart-outline'}
                 size={20}
-                color={localLike === 'like' ? '#dc2626' : '#737373'}
+                color={displayedLike === 'like' ? '#dc2626' : '#737373'}
               />
             </Animated.View>
-            {localCount > 0 && (
+            {displayedCount > 0 && (
-              <Text className="text-xs text-neutral-600" style={{ fontFamily: 'Nunito_600SemiBold' }}>{localCount}</Text>
+              <Text className="text-xs text-neutral-600" style={{ fontFamily: 'Nunito_600SemiBold' }}>{displayedCount}</Text>
             )}
           </Pressable>