Drop stale observation fields during overlay

tests/test_web_observability.py

@@ -1861,6 +1861,14 @@ def test_stale_ankara_chart_data_overlays_latest_mgm_canonical(monkeypatch):
                         "report_time": "2026-06-14T09:50:00+00:00",
                         "raw_metar": "METAR LTAC 140950Z 06013KT 9999 16/11 Q1015",
                     },
+                    "airport_current": {
+                        "temp": 16.0,
+                        "source_code": "mgm",
+                        "source_label": "MGM",
+                        "obs_time": "2026-06-14T09:50:00+00:00",
+                        "report_time": "2026-06-14T09:50:00+00:00",
+                        "raw_metar": "METAR LTAC 140950Z 06013KT 9999 16/11 Q1015",
+                    },
                     "airport_primary_today_obs": [{"time": "12:50", "temp": 16.0}],
                     "metar_today_obs": [{"time": "12:50", "temp": 16.0}],
                     "metar_recent_obs": [{"time": "12:50", "temp": 16.0}],
@@ -1918,7 +1926,10 @@ def test_stale_ankara_chart_data_overlays_latest_mgm_canonical(monkeypatch):
     assert payload["local_time"] == "17:20"
     assert payload["airport_primary_today_obs"] == [{"time": "17:20", "temp": 19.0}]
     assert "raw_metar" not in payload["current"]
+    assert "raw_metar" not in payload["airport_primary"]
     assert "report_time" not in payload["airport_primary"]
+    assert "raw_metar" not in payload["airport_current"]
+    assert "report_time" not in payload["airport_current"]
     assert payload["metar_today_obs"] == []
     assert payload["metar_recent_obs"] == []
     assert payload["metar_status"]["available_for_today"] is False

web/services/city_api.py

@@ -423,12 +423,11 @@ def _observation_source_code(block: Any) -> str:
 def _merge_latest_observation_block(base_block: Any, latest_block: Dict[str, Any]) -> Dict[str, Any]:
     base = dict(base_block) if isinstance(base_block, dict) else {}
     latest_source = _observation_source_code(latest_block)
-    base_source = _observation_source_code(base)
+    if latest_source:
-    if base_source and latest_source and base_source != latest_source:
         base = {
             key: value
             for key, value in base.items()
-            if key not in _SOURCE_BOUND_OBSERVATION_FIELDS
+            if key not in _SOURCE_BOUND_OBSERVATION_FIELDS or key in latest_block
         }
     return {**base, **latest_block}