feat(web-core): implement unread counters and new-messages divider

backend:

- add unread_count to ChatRead serialization

- compute unread_count per chat using message_receipts and hidden messages

web:

- add unread badges in chat list

- track unread boundary per chat in store

- show 'New messages' divider in message list

- update realtime flow to increment/clear unread on incoming events

app/chats/repository.py

@@ -3,6 +3,7 @@ from sqlalchemy.orm import aliased
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.chats.models import Chat, ChatMember, ChatMemberRole, ChatType
+from app.messages.models import Message, MessageHidden, MessageReceipt
 
 
 async def create_chat(db: AsyncSession, *, chat_type: ChatType, title: str | None) -> Chat:
@@ -165,3 +166,27 @@ async def get_private_counterpart_user_id(db: AsyncSession, *, chat_id: int, use
     stmt = select(ChatMember.user_id).where(ChatMember.chat_id == chat_id, ChatMember.user_id != user_id).limit(1)
     result = await db.execute(stmt)
     return result.scalar_one_or_none()
+
+
+async def get_unread_count_for_chat(db: AsyncSession, *, chat_id: int, user_id: int) -> int:
+    last_read_subquery = (
+        select(MessageReceipt.last_read_message_id)
+        .where(MessageReceipt.chat_id == chat_id, MessageReceipt.user_id == user_id)
+        .limit(1)
+        .scalar_subquery()
+    )
+    stmt = (
+        select(func.count(Message.id))
+        .outerjoin(
+            MessageHidden,
+            (MessageHidden.message_id == Message.id) & (MessageHidden.user_id == user_id),
+        )
+        .where(
+            Message.chat_id == chat_id,
+            Message.sender_id != user_id,
+            MessageHidden.id.is_(None),
+            Message.id > func.coalesce(last_read_subquery, 0),
+        )
+    )
+    result = await db.execute(stmt)
+    return int(result.scalar_one() or 0)

app/chats/schemas.py

@@ -16,6 +16,7 @@ class ChatRead(BaseModel):
     description: str | None = None
     is_public: bool = False
     is_saved: bool = False
+    unread_count: int = 0
     pinned_message_id: int | None = None
     created_at: datetime
 

app/chats/service.py

@@ -26,6 +26,8 @@ async def serialize_chat_for_user(db: AsyncSession, *, user_id: int, chat: Chat)
             if counterpart:
                 display_title = counterpart.name or counterpart.username
 
+    unread_count = await repository.get_unread_count_for_chat(db, chat_id=chat.id, user_id=user_id)
+
     return ChatRead.model_validate(
         {
             "id": chat.id,
@@ -36,6 +38,7 @@ async def serialize_chat_for_user(db: AsyncSession, *, user_id: int, chat: Chat)
             "description": chat.description,
             "is_public": chat.is_public,
             "is_saved": chat.is_saved,
+            "unread_count": unread_count,
             "pinned_message_id": chat.pinned_message_id,
             "created_at": chat.created_at,
         }