feat: move unified generation to background worker

backend/app/tasks/generation_workflow.py

@@ -0,0 +1,38 @@
+"""Background execution for unified generation workflows."""
+
+import asyncio
+
+from app.core.celery_app import celery_app
+from app.core.logging import get_logger
+from app.db.database import _get_session_factory
+from app.services.story_service import run_generation_job_service
+
+logger = get_logger(__name__)
+
+
+@celery_app.task
+def run_generation_workflow_task(job_id: str):
+    """Execute one accepted generation job in the Celery worker."""
+
+    logger.info("generation_workflow_task_started", job_id=job_id)
+
+    async def _run():
+        session_factory = _get_session_factory()
+        async with session_factory() as session:
+            return await run_generation_job_service(job_id, session)
+
+    try:
+        result = asyncio.run(_run())
+        logger.info(
+            "generation_workflow_task_completed",
+            job_id=job_id,
+            executed=bool(result),
+        )
+        return {"job_id": job_id, "executed": bool(result)}
+    except Exception as exc:
+        logger.error(
+            "generation_workflow_task_failed",
+            job_id=job_id,
+            error=str(exc),
+        )
+        raise