fix(analytics): address review-bot PR B fixes (#113)

SQL (data/sql/94_mv_layout_velocity.sql):
- 🟠 idempotency WARN comment перед DROP CASCADE
- 🟡 WITH NO DATA + REFRESH after CREATE INDEX (меньше lock duration)
- 🟡 WHERE cm.objective_group = 'Екатеринбург' (cross-region Cartesian защита)
- 🟡 COMMENT ON MATERIALIZED VIEW с источниками + refresh механизмом

Python (services/site_finder/layout_velocity_refresh.py):
- 🟡 db.commit() после REFRESH (visibility через connection pool)
- 🟡 убрать f-string в SQL — две явных text() ветки
- 🟡 try/except OperationalError fallback на non-concurrent

backend/app/services/site_finder/layout_velocity_refresh.py

@@ -16,6 +16,7 @@ from __future__ import annotations
 import logging
 
 from sqlalchemy import text
+from sqlalchemy.exc import OperationalError
 from sqlalchemy.orm import Session
 
 logger = logging.getLogger(__name__)
@@ -34,8 +35,22 @@ def refresh_layout_velocity(db: Session, *, concurrently: bool = True) -> int:
     Returns:
         Row count in the MV after refresh (for observability / alerting).
     """
-    mode = "CONCURRENTLY" if concurrently else ""
-    db.execute(text(f"REFRESH MATERIALIZED VIEW {mode} mv_layout_velocity"))
+    try:
+        if concurrently:
+            db.execute(text("REFRESH MATERIALIZED VIEW CONCURRENTLY mv_layout_velocity"))
+        else:
+            db.execute(text("REFRESH MATERIALIZED VIEW mv_layout_velocity"))
+        db.commit()
+    except OperationalError as e:
+        if concurrently and "cannot refresh materialized view" in str(e).lower():
+            logger.warning(
+                "CONCURRENTLY failed (MV likely not populated), falling back to non-concurrent"
+            )
+            db.rollback()
+            db.execute(text("REFRESH MATERIALIZED VIEW mv_layout_velocity"))
+            db.commit()
+        else:
+            raise
     row = db.execute(text("SELECT COUNT(*) FROM mv_layout_velocity")).first()
     count = int(row[0]) if row else 0
     logger.info("mv_layout_velocity refreshed: %d rows", count)

data/sql/94_mv_layout_velocity.sql

@@ -22,6 +22,13 @@
 --
 -- Deploy: auto-applied by deploy.yml via _schema_migrations tracking.
 -- Dependencies: none (no views depend on this MV at creation time).
+--
+-- WARN: Re-apply этого файла (DR / lost _schema_migrations entry / dev local)
+--       снесёт MV + CASCADE удалит зависимости (e.g. future /best-layouts views).
+--       После re-apply ПЕРВЫЙ refresh должен быть concurrently=False
+--       (CONCURRENTLY требует уже populated MV — упадёт на пустой).
+--       Tracking table `_schema_migrations` нормально предотвращает re-apply,
+--       но добавлен comment как safety reminder.
 
 BEGIN;
 
@@ -59,9 +66,12 @@ JOIN objective_complex_mapping cm
     ON cm.objective_complex_name = l.project_name
 WHERE l.room_bucket IS NOT NULL
   AND cm.domrf_obj_id IS NOT NULL
-GROUP BY cm.domrf_obj_id, l.room_bucket;
+  AND cm.objective_group = 'Екатеринбург'  -- защита от cross-region Cartesian при future multi-city
+GROUP BY cm.domrf_obj_id, l.room_bucket
+WITH NO DATA;
 
 -- UNIQUE index required for REFRESH CONCURRENTLY (future periodic refreshes)
+-- Created on empty MV → instant, no lock duration on data
 CREATE UNIQUE INDEX mv_layout_velocity_pk
     ON mv_layout_velocity (obj_id, room_bucket);
 
@@ -69,4 +79,12 @@ CREATE UNIQUE INDEX mv_layout_velocity_pk
 CREATE INDEX mv_layout_velocity_obj_idx
     ON mv_layout_velocity (obj_id);
 
+-- Initial populate (non-concurrent — MV was just created, CONCURRENTLY not allowed on empty MV)
+REFRESH MATERIALIZED VIEW mv_layout_velocity;
+
+COMMENT ON MATERIALIZED VIEW mv_layout_velocity IS
+  'Per-(obj_id, room_bucket) deals aggregation за last 24 months. '
+  'Source: objective_corpus_room_month × objective_complex_mapping (EKB only). '
+  'Refresh via layout_velocity_refresh.py (concurrently=True after initial populate).';
+
 COMMIT;