Use indexed raw observation history lookup

src/database/db_manager.py

@@ -1307,20 +1307,25 @@ class DBManager:
             return []
         safe_limit = max(1, min(int(limit or 1000), 5000))
         safe_minutes = max(1, min(int(minutes or 60), 7 * 24 * 60))
-        cutoff_ts = datetime.now().timestamp() - safe_minutes * 60
+        cutoff_dt = datetime.now(timezone.utc) - timedelta(minutes=safe_minutes)
+        cutoff_observed_at = cutoff_dt.replace(microsecond=0).isoformat()
         with self._get_connection() as conn:
             conn.row_factory = sqlite3.Row
             rows = conn.execute(
                 """
+                SELECT *
+                FROM (
                     SELECT *
                     FROM raw_observation_store
                     WHERE source = ?
                       AND city = ?
-                  AND created_at_ts >= ?
+                      AND observed_at >= ?
-                ORDER BY observed_at ASC, fetched_at ASC, created_at_ts ASC
+                    ORDER BY observed_at DESC, fetched_at DESC, created_at_ts DESC
                     LIMIT ?
+                )
+                ORDER BY observed_at ASC, fetched_at ASC, created_at_ts ASC
                 """,
-                (normalized_source, normalized_city, cutoff_ts, safe_limit),
+                (normalized_source, normalized_city, cutoff_observed_at, safe_limit),
             ).fetchall()
         out: List[Dict[str, Any]] = []
         for row in rows:

tests/test_observation_collector.py

@@ -182,15 +182,19 @@ def test_raw_observation_store_records_latest_observation(tmp_path):
 
 
 def test_raw_observation_store_lists_source_city_history(tmp_path):
+    from datetime import datetime, timedelta, timezone
+
     from src.database.db_manager import DBManager
 
     db = DBManager(str(tmp_path / "polyweather.db"))
+    first_observed_at = (datetime.now(timezone.utc) - timedelta(minutes=2)).replace(microsecond=0).isoformat()
+    second_observed_at = (datetime.now(timezone.utc) - timedelta(minutes=1)).replace(microsecond=0).isoformat()
     db.append_raw_observation(
         source="amsc_awos",
         city="Chengdu",
         value=25.6,
-        observed_at="2026-06-15T11:04:00+00:00",
+        observed_at=first_observed_at,
-        fetched_at="2026-06-15T11:04:30+00:00",
+        fetched_at=first_observed_at,
         station_code="ZUUU",
         payload={"temp_c": 25.6},
     )
@@ -198,8 +202,8 @@ def test_raw_observation_store_lists_source_city_history(tmp_path):
         source="amsc_awos",
         city="chengdu",
         value=25.4,
-        observed_at="2026-06-15T11:08:00+00:00",
+        observed_at=second_observed_at,
-        fetched_at="2026-06-15T11:08:30+00:00",
+        fetched_at=second_observed_at,
         station_code="ZUUU",
         payload={"temp_c": 25.4},
     )
@@ -207,8 +211,8 @@ def test_raw_observation_store_lists_source_city_history(tmp_path):
     rows = db.list_raw_observation_history("amsc_awos", "chengdu", minutes=60, limit=10)
 
     assert [row["observed_at"] for row in rows] == [
-        "2026-06-15T11:04:00+00:00",
+        first_observed_at,
-        "2026-06-15T11:08:00+00:00",
+        second_observed_at,
     ]
     assert rows[-1]["payload"]["temp_c"] == 25.4