Refactor dewar query to use latest event subquery.

Replaces the previous query logic with a subquery to find the latest logistics event for each dewar. Ensures that only dewars with the most recent "beamline" event are retrieved, improving query accuracy and clarity.

backend/app/routers/puck.py

@@ -394,13 +394,32 @@ async def get_pucks_by_slot(slot_identifier: str, db: Session = Depends(get_db))
             status_code=404, detail=f"Slot not found for identifier {slot_identifier}"
         )
 
-    # Fetch dewars in the slot
+    # Subquery to find the latest event for each dewar
+    latest_event_subquery = (
+        db.query(
+            LogisticsEventModel.dewar_id.label("dewar_id"),
+            func.max(LogisticsEventModel.timestamp).label("latest_event_time"),
+        )
+        .group_by(LogisticsEventModel.dewar_id)
+        .subquery(name="latest_event_subquery")
+    )
+
+    # Main query to fetch dewars where the latest event is "beamline"
     dewars = (
         db.query(DewarModel)
         .join(LogisticsEventModel, DewarModel.id == LogisticsEventModel.dewar_id)
+        .join(
+            latest_event_subquery,
+            (LogisticsEventModel.dewar_id == latest_event_subquery.c.dewar_id)
+            & (
+                LogisticsEventModel.timestamp
+                == latest_event_subquery.c.latest_event_time
+            ),  # Match latest event
+        )
         .filter(
             LogisticsEventModel.slot_id == slot_id,
-            LogisticsEventModel.event_type == "beamline",
+            LogisticsEventModel.event_type
+            == "beamline",  # Ensure latest event is "beamline"
         )
         .all()
     )