On-board package hover traces from the carrier's current position (ISS-040)

lib/mapData.ts

@@ -112,6 +112,32 @@ export function hoverRouteGeoJson(
   };
 }
 
+// ISS-040 (v0.23.2): the on-board package hover trace — same shape as hoverRouteGeoJson but the
+// start is a live COORDINATE (the carrier plane's current position), not an airport ICAO: once the
+// plane has departed with cargo still loaded, the preview must begin where it actually is. Empty
+// collection when the destination is missing from the dataset — never guessed.
+export function hoverTraceGeoJson(
+  from: AirportCoord,
+  toIcao: string,
+  airportsByIcao: ReadonlyMap<string, AirportCoord>,
+): FeatureCollection<MapLineFeature> {
+  const to = airportsByIcao.get(toIcao);
+  if (!to) return EMPTY_LINES;
+  return {
+    type: 'FeatureCollection',
+    features: [
+      {
+        type: 'Feature',
+        geometry: {
+          type: 'LineString',
+          coordinates: greatCircleArc(from, to),
+        },
+        properties: { planeId: '' }, // no owning plane — a pure hover overlay
+      },
+    ],
+  };
+}
+
 // One LineString per FLYING plane — its current leg from locationIcao to dest_icao.
 // Grounded planes draw nothing; a flying plane missing either endpoint from the
 // dataset is skipped, never guessed. The line is sampled along the great circle