fix: live comment sync in shared chats

- Added a method to find existing notifications by mention ID to prevent duplicate notifications.
- Updated notify_new_mention to check for existing notifications before creating a new one, ensuring idempotency.
- Implemented error handling for race conditions during notification creation, allowing retrieval of existing notifications in case of duplicate key errors.
- Improved documentation for clarity on the use of mention_id for idempotency.

surfsense_backend/app/services/notification_service.py

@@ -623,6 +623,28 @@ class MentionNotificationHandler(BaseNotificationHandler):
     def __init__(self):
         super().__init__("new_mention")
 
+    async def find_notification_by_mention(
+        self,
+        session: AsyncSession,
+        mention_id: int,
+    ) -> Notification | None:
+        """
+        Find an existing notification by mention ID.
+
+        Args:
+            session: Database session
+            mention_id: The mention ID to search for
+
+        Returns:
+            Notification if found, None otherwise
+        """
+        query = select(Notification).where(
+            Notification.type == self.notification_type,
+            Notification.notification_metadata["mention_id"].astext == str(mention_id),
+        )
+        result = await session.execute(query)
+        return result.scalar_one_or_none()
+
     async def notify_new_mention(
         self,
         session: AsyncSession,
@@ -641,11 +663,12 @@ class MentionNotificationHandler(BaseNotificationHandler):
     ) -> Notification:
         """
         Create notification when a user is @mentioned in a comment.
+        Uses mention_id for idempotency to prevent duplicate notifications.
 
         Args:
             session: Database session
             mentioned_user_id: User who was mentioned
-            mention_id: ID of the mention record
+            mention_id: ID of the mention record (used for idempotency)
             comment_id: ID of the comment containing the mention
             message_id: ID of the message being commented on
             thread_id: ID of the chat thread
@@ -658,8 +681,16 @@ class MentionNotificationHandler(BaseNotificationHandler):
             search_space_id: Search space ID
 
         Returns:
-            Notification: The created notification
+            Notification: The created or existing notification
         """
+        # Check if notification already exists for this mention (idempotency)
+        existing = await self.find_notification_by_mention(session, mention_id)
+        if existing:
+            logger.info(
+                f"Notification already exists for mention {mention_id}, returning existing"
+            )
+            return existing
+
         title = f"{author_name} mentioned you"
         message = content_preview[:100] + ("..." if len(content_preview) > 100 else "")
 
@@ -676,21 +707,34 @@ class MentionNotificationHandler(BaseNotificationHandler):
             "content_preview": content_preview[:200],
         }
 
-        notification = Notification(
-            user_id=mentioned_user_id,
-            search_space_id=search_space_id,
-            type=self.notification_type,
-            title=title,
-            message=message,
-            notification_metadata=metadata,
-        )
-        session.add(notification)
-        await session.commit()
-        await session.refresh(notification)
-        logger.info(
-            f"Created new_mention notification {notification.id} for user {mentioned_user_id}"
-        )
-        return notification
+        try:
+            notification = Notification(
+                user_id=mentioned_user_id,
+                search_space_id=search_space_id,
+                type=self.notification_type,
+                title=title,
+                message=message,
+                notification_metadata=metadata,
+            )
+            session.add(notification)
+            await session.commit()
+            await session.refresh(notification)
+            logger.info(
+                f"Created new_mention notification {notification.id} for user {mentioned_user_id}"
+            )
+            return notification
+        except Exception as e:
+            # Handle race condition - if duplicate key error, try to fetch existing
+            await session.rollback()
+            if "duplicate key" in str(e).lower() or "unique constraint" in str(e).lower():
+                logger.warning(
+                    f"Duplicate notification detected for mention {mention_id}, fetching existing"
+                )
+                existing = await self.find_notification_by_mention(session, mention_id)
+                if existing:
+                    return existing
+            # Re-raise if not a duplicate key error or couldn't find existing
+            raise
 
 
 class NotificationService:

surfsense_web/hooks/use-comments-electric.ts

@@ -15,6 +15,9 @@ import type { SyncHandle } from "@/lib/electric/client";
 import { useElectricClient } from "@/lib/electric/context";
 import { cacheKeys } from "@/lib/query-client/cache-keys";
 
+// Debounce delay for stream updates (ms)
+const STREAM_UPDATE_DEBOUNCE_MS = 100;
+
 // Raw comment from PGlite local database
 interface RawCommentRow {
 	id: number;
@@ -208,6 +211,7 @@ export function useCommentsElectric(threadId: number | null) {
 	const syncHandleRef = useRef<SyncHandle | null>(null);
 	const liveQueryRef = useRef<{ unsubscribe: () => void } | null>(null);
 	const syncKeyRef = useRef<string | null>(null);
+	const streamUpdateDebounceRef = useRef<ReturnType<typeof setTimeout> | null>(null);
 
 	// Stable callback that uses refs for fresh values
 	const updateReactQueryCache = useCallback((rows: RawCommentRow[]) => {
@@ -275,6 +279,30 @@ export function useCommentsElectric(threadId: number | null) {
 
 				// Set up live query for real-time updates
 				await setupLiveQuery();
+
+				// Subscribe to the sync stream for real-time updates from Electric SQL
+				// This ensures we catch updates even if PGlite live query misses them
+				if (handle.stream) {
+					const stream = handle.stream as { subscribe?: (callback: (messages: unknown[]) => void) => void };
+					if (typeof stream.subscribe === "function") {
+						stream.subscribe((messages: unknown[]) => {
+							if (!mounted) return;
+							// When Electric sync receives new data, refresh from PGlite
+							// This handles cases where live query might miss the update
+							if (messages && messages.length > 0) {
+								// Debounce the refresh to avoid excessive queries
+								if (streamUpdateDebounceRef.current) {
+									clearTimeout(streamUpdateDebounceRef.current);
+								}
+								streamUpdateDebounceRef.current = setTimeout(() => {
+									if (mounted) {
+										fetchAndUpdateCache();
+									}
+								}, STREAM_UPDATE_DEBOUNCE_MS);
+							}
+						});
+					}
+				}
 			} catch {
 				// Sync failed - will retry on next mount
 			}
@@ -348,6 +376,12 @@ export function useCommentsElectric(threadId: number | null) {
 			mounted = false;
 			syncKeyRef.current = null;
 
+			// Clear debounce timeout
+			if (streamUpdateDebounceRef.current) {
+				clearTimeout(streamUpdateDebounceRef.current);
+				streamUpdateDebounceRef.current = null;
+			}
+
 			if (syncHandleRef.current) {
 				syncHandleRef.current.unsubscribe();
 				syncHandleRef.current = null;