P1-b: don't let LBS/WIFI fixes overwrite a fresh GPS fix in live view

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/projectors/live_positions.py

@@ -24,6 +24,14 @@ log = structlog.get_logger("projector.live_positions")
 DRAIN_BATCH = 500
 PROJECTED_FLAG_KEY = "live_positions_projected_at"
 
+# Low-accuracy positioning modes (cell-tower / wifi) reported in Tracksolid's
+# `posType`. These can be kilometres off a real GPS fix, so we don't let one
+# overwrite a *fresh* GPS fix in the live view (it would teleport the marker).
+# A GPS fix older than this window does yield to LBS/WIFI, so a genuinely
+# GPS-dark vehicle still updates rather than freezing forever.
+LOW_ACCURACY_POS_TYPES = ("LBS", "WIFI")
+GPS_PREFERENCE_WINDOW_SQL = "interval '10 minutes'"
+
 
 _PLATE_FROM_DEVICE_NAME = re.compile(r"^.* - (.+?)(?:_cam|_CAM)?$")
 _CAMERA_NAME_RE = re.compile(r"_cam$", re.IGNORECASE)
@@ -190,6 +198,13 @@ async def _project_one(
                device_name        = EXCLUDED.device_name,
                pos_type           = EXCLUDED.pos_type
          WHERE EXCLUDED.occurred_at > state.live_positions.occurred_at
+           AND NOT COALESCE(
+                   EXCLUDED.pos_type = ANY (%s)
+               AND state.live_positions.pos_type = 'GPS'
+               AND state.live_positions.occurred_at
+                   > now() - """ + GPS_PREFERENCE_WINDOW_SQL + """,
+               false
+               )
         """,
         (
             imei, vehicle_id, occurred_at, geom_wkt,
@@ -204,6 +219,7 @@ async def _project_one(
             payload.get("satellites"),
             payload.get("device_name"),
             payload.get("pos_type"),
+            list(LOW_ACCURACY_POS_TYPES),
         ),
     )