fix: avoid sqlalchemy session concurrency

Author: lkstrp

src/pypsa_app/backend/api/routes/runs.py

@@ -34,8 +34,11 @@
     RunSummary,
 )
 from pypsa_app.backend.services.backend_registry import backend_registry
+from pypsa_app.backend.services.callback import (
+    _build_payload,
+    post_callback_sync,
+)
 from pypsa_app.backend.services.run import SnakedispatchClient, SnakedispatchError
-from pypsa_app.backend.services.callback import fire_callback_sync
 from pypsa_app.backend.services.sync import (
     SYNCED_STATUSES,
     sync_run_from_job,
@@ -292,9 +295,11 @@ def get_run(
                 if needs_callback:
                     # TODO: replace with proper async callback or
                     # FastAPI BackgroundTasks.
+                    url = str(run.callback_url)
+                    payload = _build_payload(run)
                     threading.Thread(
-                        target=fire_callback_sync,
-                        args=(run,),
+                        target=post_callback_sync,
+                        args=(url, payload),
                         daemon=True,
                     ).start()
             except SnakedispatchError:
@@ -397,8 +402,10 @@ def cancel_run(
         if needs_callback:
             # TODO: replace with proper async callback or
             # FastAPI BackgroundTasks.
+            url = str(run.callback_url)
+            payload = _build_payload(run)
             threading.Thread(
-                target=fire_callback_sync, args=(run,), daemon=True
+                target=post_callback_sync, args=(url, payload), daemon=True
             ).start()
     except SnakedispatchError as e:
         if e.status_code in (404, 409):
@@ -407,8 +414,10 @@ def cancel_run(
                 db.commit()
                 # TODO: replace with proper async callback or
                 # FastAPI BackgroundTasks.
+                url = str(run.callback_url)
+                payload = _build_payload(run)
                 threading.Thread(
-                    target=fire_callback_sync, args=(run,), daemon=True
+                    target=post_callback_sync, args=(url, payload), daemon=True
                 ).start()
         else:
             raise

src/pypsa_app/backend/schemas/run.py

@@ -2,7 +2,6 @@
 
 import uuid
 from datetime import datetime
-
 from urllib.parse import urlparse
 
 from pydantic import BaseModel, ConfigDict, Field, HttpUrl, field_validator

src/pypsa_app/backend/services/callback.py

@@ -13,23 +13,26 @@ def _build_payload(run: Run) -> dict:
     return {"run_id": str(run.job_id), "status": run.status.value}
 
 
-def fire_callback_sync(run: Run) -> None:
-    """POST to the run's callback URL (blocking)."""
-    if not run.callback_url:
-        return
-    url = str(run.callback_url)
-    payload = _build_payload(run)
+def post_callback_sync(url: str, payload: dict) -> None:
+    """POST to a callback URL (blocking)."""
     try:
         httpx.post(url, json=payload, timeout=5.0, follow_redirects=False)
     except Exception:
         logger.warning(
             "Callback failed for run %s to %s",
-            payload["run_id"],
+            payload.get("run_id"),
             url,
             exc_info=True,
         )
 
 
+def fire_callback_sync(run: Run) -> None:
+    """POST to the run's callback URL (blocking)."""
+    if not run.callback_url:
+        return
+    post_callback_sync(str(run.callback_url), _build_payload(run))
+
+
 async def fire_callback_async(url: str, payload: dict) -> None:
     """POST to a callback URL (async). Used by the background sync loop."""
     try:

src/pypsa_app/backend/services/sync.py

@@ -11,8 +11,8 @@
 
 from pypsa_app.backend.database import SessionLocal
 from pypsa_app.backend.models import Run, RunStatus
-from pypsa_app.backend.services.callback import fire_callback_async
 from pypsa_app.backend.services.backend_registry import backend_registry
+from pypsa_app.backend.services.callback import fire_callback_async
 from pypsa_app.backend.tasks import import_run_outputs_task
 
 logger = logging.getLogger(__name__)
@@ -143,7 +143,9 @@ async def run_sync_loop(interval: float = 10.0) -> None:
         try:
             callbacks = await asyncio.to_thread(sync_non_terminal_runs)
             for cb in callbacks:
-                task = asyncio.create_task(fire_callback_async(cb["url"], cb["payload"]))
+                task = asyncio.create_task(
+                    fire_callback_async(cb["url"], cb["payload"])
+                )
                 _background_tasks.add(task)
                 task.add_done_callback(_background_tasks.discard)
         except Exception:

src/pypsa_app/backend/tasks.py

@@ -12,6 +12,7 @@
 from pypsa_app.backend.database import SessionLocal
 from pypsa_app.backend.models import Run, RunStatus, SnakedispatchBackend
 from pypsa_app.backend.schemas.task import TaskResultResponse
+from pypsa_app.backend.services.callback import fire_callback_sync
 from pypsa_app.backend.services.network import import_network_file
 from pypsa_app.backend.services.callback import fire_callback_sync
 from pypsa_app.backend.services.run import SnakedispatchClient