feat: v0.22.0 — ISS-022/025/027 hover route trace on job list, on-board rows and relocation panel

lib/mapData.ts

@@ -85,6 +85,33 @@ export function greatCircleArc(from: AirportCoord, to: AirportCoord): [number, n
   return coords;
 }
 
+// ISS-022/025/027 (v0.22.0): the hover route trace — one great-circle LineString between two
+// airports, drawn top-most while a panel row hovers (job-list rows, on-board cargo rows, the
+// Relocate section). Empty collection when either endpoint is missing from the dataset — never
+// guessed; the '' sentinel (no hovered target) resolves to nothing and yields the same.
+export function hoverRouteGeoJson(
+  fromIcao: string,
+  toIcao: string,
+  airportsByIcao: ReadonlyMap<string, AirportCoord>,
+): FeatureCollection<MapLineFeature> {
+  const from = airportsByIcao.get(fromIcao);
+  const to = airportsByIcao.get(toIcao);
+  if (!from || !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