feat(threads): support nested replies in thread API and panel

app/messages/repository.py

@@ -152,6 +152,34 @@ async def list_message_thread(
     return list(result.scalars().all())
 
 
+async def list_messages_by_parent_ids(
+    db: AsyncSession,
+    *,
+    chat_id: int,
+    user_id: int,
+    parent_ids: list[int],
+    limit: int = 200,
+) -> list[Message]:
+    if not parent_ids:
+        return []
+    stmt = (
+        select(Message)
+        .outerjoin(
+            MessageHidden,
+            (MessageHidden.message_id == Message.id) & (MessageHidden.user_id == user_id),
+        )
+        .where(
+            Message.chat_id == chat_id,
+            MessageHidden.id.is_(None),
+            Message.reply_to_message_id.in_(parent_ids),
+        )
+        .order_by(Message.id.asc())
+        .limit(max(1, min(limit, 500)))
+    )
+    result = await db.execute(stmt)
+    return list(result.scalars().all())
+
+
 async def delete_message(db: AsyncSession, message: Message) -> None:
     await db.delete(message)
 

app/messages/service.py

@@ -188,7 +188,29 @@ async def get_message_thread(
     if not root:
         raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Message not found")
     await ensure_chat_membership(db, chat_id=root.chat_id, user_id=user_id)
-    return await repository.list_message_thread(db, root_message_id=message_id, user_id=user_id, limit=limit)
+    safe_limit = max(1, min(limit, 500))
+    collected: dict[int, Message] = {root.id: root}
+    frontier: list[int] = [root.id]
+    remaining = safe_limit - 1
+    while frontier and remaining > 0:
+        batch = await repository.list_messages_by_parent_ids(
+            db,
+            chat_id=root.chat_id,
+            user_id=user_id,
+            parent_ids=frontier,
+            limit=min(remaining, 200),
+        )
+        next_frontier: list[int] = []
+        for message in batch:
+            if message.id in collected:
+                continue
+            collected[message.id] = message
+            next_frontier.append(message.id)
+            remaining -= 1
+            if remaining <= 0:
+                break
+        frontier = next_frontier
+    return sorted(collected.values(), key=lambda item: item.id)
 
 
 async def update_message(