krt_lookup (×2), okn_lookup, ppt_tep_lookup, riasurt_lookup, premises_lookup,
ird_analyze._krt_at, and product_scoring._poi_weight_sum (both the centroid
lookup and the compute_poi_weighted_top7 call) swallowed db.execute failures
without a SAVEPOINT, leaving the shared analyze/report session aborted for
later queries. Wrap each swallow site in db.begin_nested(). locations.py's
pass-1 infra/POI block uses a plain db.rollback() instead — its session is
owned by the weekly location_refresh Celery task (own SessionLocal, verified
single caller-chain), not shared, and nothing is pending at that point.
Refs #2464 (cluster A session-poisoning, Wave 2).
