Use sync SQLAlchemy in Celery worker - fixes asyncpg connection issues

backend/app/core/database.py

@@ -1,7 +1,9 @@
 from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession, async_sessionmaker
-from sqlalchemy.orm import DeclarativeBase
+from sqlalchemy import create_engine
+from sqlalchemy.orm import DeclarativeBase, sessionmaker
 from app.core.config import settings
 
+# Async engine for FastAPI
 engine = create_async_engine(
     settings.database_url,
     echo=settings.environment == "development",
@@ -15,6 +17,19 @@ AsyncSessionLocal = async_sessionmaker(
     expire_on_commit=False,
 )
 
+# Sync engine for Celery workers (Celery + asyncio don't mix well)
+# Convert async URL to sync: postgresql+asyncpg:// → postgresql+psycopg2://
+sync_url = settings.database_url.replace("postgresql+asyncpg://", "postgresql+psycopg2://")
+sync_engine = create_engine(
+    sync_url,
+    echo=False,
+    pool_size=5,
+    max_overflow=10,
+    pool_pre_ping=True,
+)
+
+SyncSessionLocal = sessionmaker(sync_engine, expire_on_commit=False)
+
 
 class Base(DeclarativeBase):
     pass
@@ -29,4 +44,4 @@ async def get_db():
             await session.rollback()
             raise
         finally:
-            await session.close()
+            await session.close()