Fix storage lock contention: reduce lock holds across 6 hot paths

- get_blob_for_post: 3 sequential locks → 1 combined acquisition
- prefetch_blobs_from_peer: lock only for DB reads, blob checks outside lock
- fetch_engagement_from_peer: explicit lock release before next network I/O
- serve_post: 4 locks (2 redundant) → 2
- run_replication_check: 2 locks → 1 combined
- Badge cycle: N+2 IPC calls → 1 (new get_badge_counts command)
- Follow timeout: 15s cap on auto-sync-on-follow to prevent UI hang
- Notification clearing: clear system notifications on conversation read

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/tauri-app/src/lib.rs

@@ -116,6 +116,13 @@ struct StatsDto {
     follow_count: usize,
 }
 
+#[derive(Serialize)]
+#[serde(rename_all = "camelCase")]
+struct BadgeCountsDto {
+    new_feed: usize,
+    new_engagement: usize,
+}
+
 #[derive(Serialize)]
 #[serde(rename_all = "camelCase")]
 struct RedundancyDto {
@@ -666,11 +673,16 @@ async fn follow_node(state: State<'_, AppState>, node_id_hex: String) -> Result<
     let node = state.inner();
     let nid = parse_node_id(&node_id_hex)?;
     node.follow(&nid).await.map_err(|e| e.to_string())?;
-    // Auto-sync: pull posts from the followed peer in the background
+    // Auto-sync: pull posts from the followed peer in the background (15s timeout)
     let node_clone = state.inner().clone();
     tokio::spawn(async move {
-        if let Err(e) = node_clone.sync_with(nid).await {
-            tracing::debug!(error = %e, "Auto-sync after follow failed (peer may not be connected)");
+        match tokio::time::timeout(
+            std::time::Duration::from_secs(15),
+            node_clone.sync_with(nid),
+        ).await {
+            Ok(Ok(())) => {}
+            Ok(Err(e)) => tracing::debug!(error = %e, "Auto-sync after follow failed"),
+            Err(_) => tracing::debug!("Auto-sync after follow timed out (15s)"),
         }
     });
     Ok(())
@@ -1399,6 +1411,54 @@ async fn get_seen_engagement(
     }))
 }
 
+#[tauri::command]
+async fn get_badge_counts(
+    state: State<'_, AppState>,
+    last_feed_view_ms: u64,
+) -> Result<BadgeCountsDto, String> {
+    let node = state.inner();
+    let storage = node.storage.lock().await;
+
+    // Feed badge: count non-DM posts from others newer than last_feed_view_ms
+    let feed_posts = storage.get_feed().map_err(|e| e.to_string())?;
+    let new_feed = feed_posts.iter()
+        .filter(|(id, p, _vis)| {
+            p.author != node.node_id
+                && p.timestamp_ms > last_feed_view_ms
+                && !matches!(
+                    storage.get_post_intent(id).ok().flatten(),
+                    Some(VisibilityIntent::Direct(_))
+                )
+        })
+        .count();
+
+    // My Posts badge: count own non-DM posts with unseen engagement
+    let all_posts = storage.list_posts_reverse_chron().map_err(|e| e.to_string())?;
+    let mut new_engagement = 0usize;
+    for (id, post, _vis) in &all_posts {
+        if post.author != node.node_id { continue; }
+        // Skip DMs
+        if matches!(
+            storage.get_post_intent(id).ok().flatten(),
+            Some(VisibilityIntent::Direct(_))
+        ) { continue; }
+        let total_reacts: u64 = storage.get_reaction_counts(id, &node.node_id)
+            .unwrap_or_default()
+            .iter()
+            .map(|(_, count, _)| *count)
+            .sum();
+        let total_comments = storage.get_comment_count(id).unwrap_or(0);
+        if total_reacts > 0 || total_comments > 0 {
+            let (seen_r, seen_c) = storage.get_seen_engagement(id).unwrap_or((0, 0));
+            if total_reacts > seen_r as u64 || total_comments > seen_c as u64 {
+                new_engagement += 1;
+            }
+        }
+    }
+
+    Ok(BadgeCountsDto { new_feed, new_engagement })
+}
+
 #[tauri::command]
 async fn get_last_read_message(
     state: State<'_, AppState>,
@@ -2057,6 +2117,7 @@ pub fn run() {
             mark_post_seen,
             mark_conversation_read,
             get_seen_engagement,
+            get_badge_counts,
             get_last_read_message,
             generate_share_link,
         ])