Add generation harness runtime

backend/app/services/harness/control.py

@@ -0,0 +1,48 @@
+"""Execution control helpers for generation harness workflows."""
+
+from typing import TYPE_CHECKING
+
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.services.generation_jobs import finish_generation_job
+
+if TYPE_CHECKING:
+    from app.db.models import GenerationJob, Story
+
+
+class GenerationJobCanceledError(Exception):
+    """Raised when a running worker job has been canceled by the user."""
+
+
+class ExecutionControl:
+    """Runtime control surface for cancelable generation workflows."""
+
+    def __init__(self, db: AsyncSession):
+        self.db = db
+
+    async def stop_if_cancel_requested(
+        self,
+        *,
+        job: "GenerationJob | None",
+        story: "Story | None" = None,
+    ) -> None:
+        """Stop a worker-owned job at the next safe checkpoint after cancellation."""
+
+        if job is None:
+            return
+
+        await self.db.refresh(job)
+        if job.current_step != "cancel_requested":
+            return
+
+        await finish_generation_job(
+            self.db,
+            job=job,
+            story=story,
+            status="canceled",
+            current_step="generation_canceled",
+            error_message="Generation canceled by user.",
+            message="Generation job was canceled after a user request.",
+        )
+        raise GenerationJobCanceledError()
+