wrongmove: fix DetachedInstanceError in daily market aggregator task

`compute_aggregate_snapshot` returns ORM rows that were created inside
a `with Session(engine)` block — by the time the Celery task tries to
serialise their attributes into the result dict the session has closed,
triggering SQLAlchemy's DetachedInstanceError. Combined with acks_late
this caused the task to be redelivered repeatedly (4× in the first
manual trigger).

Fix: drop the per-row dict-serialisation in the task return — keep just
`aggregates_written: int`. The per-band stats are already logged by the
aggregator's own info-level lines, so no observability is lost.

Caught when manually firing the task on prod to seed today's snapshot
before the 04:00 UTC daily fire. Aggregator itself ran fine (the rows
were written before the session closed); only the post-return access
was broken.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tasks/market_tasks.py

@@ -32,26 +32,20 @@ def compute_daily_market_aggregates_task(self: Any) -> dict[str, Any]:
     celery_logger.info("Starting daily market aggregator (task=%s)", self.request.id)
     per_listing = market_aggregator.update_per_listing_trend(engine)
     aggregates = market_aggregator.compute_aggregate_snapshot(engine)
+    # Materialise only the count — the row objects came from a session
+    # that's already closed, so accessing any lazy-loaded attribute would
+    # raise DetachedInstanceError. The aggregator's own logger lines have
+    # already printed the per-band stats.
+    aggregates_count = len(aggregates)
     result = {
         "status": "ok",
         "per_listing": per_listing,
-        "aggregates": [
+        "aggregates_written": aggregates_count,
-            {
-                "snapshot_date": a.snapshot_date.isoformat(),
-                "listing_type": a.listing_type,
-                "min_bedrooms": a.min_bedrooms,
-                "max_bedrooms": a.max_bedrooms,
-                "listing_count": a.listing_count,
-                "median_total_price": a.median_total_price,
-                "median_qmprice": a.median_qmprice,
-            }
-            for a in aggregates
-        ],
     }
     celery_logger.info(
-        "Daily market aggregator complete: rent_updated=%s buy_updated=%s aggregates=%s",
+        "Daily market aggregator complete: rent_updated=%s buy_updated=%s aggregates=%d",
         per_listing.get("rent_updated"),
         per_listing.get("buy_updated"),
-        len(aggregates),
+        aggregates_count,
     )
     return result