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

lib/mapData.test.ts

@@ -1,6 +1,6 @@
 import { describe, expect, it } from 'vitest';
 import type { StateSnapshot } from './game/state';
-import { planesGeoJson, routesGeoJson, hoverRouteGeoJson, greatCircleArc, ROUTE_ARC_SEGMENTS, type AirportCoord } from './mapData';
+import { planesGeoJson, routesGeoJson, hoverRouteGeoJson, hoverTraceGeoJson, greatCircleArc, ROUTE_ARC_SEGMENTS, type AirportCoord } from './mapData';
 import { haversineKm } from './geo';
 
 const AIRPORTS = new Map<string, AirportCoord>([
@@ -176,6 +176,23 @@ describe('hoverRouteGeoJson (ISS-022/025/027 v0.22.0 — hover route trace)', ()
   });
 });
 
+describe('hoverTraceGeoJson (ISS-040 v0.23.2 — on-board package trace from the carrier\'s live position)', () => {
+  it('draws one great-circle line from the given start coord to the dest airport with exact endpoints', () => {
+    const from = { lat: 51.2, lon: 9.1 }; // a mid-flight position — not an airport
+    const fc = hoverTraceGeoJson(from, 'EHAM', AIRPORTS);
+    expect(fc.features).toHaveLength(1);
+    expect(fc.features[0].properties).toEqual({ planeId: '' }); // pure overlay — no owning plane
+    const coords = fc.features[0].geometry.coordinates;
+    expect(coords.length).toBe(ROUTE_ARC_SEGMENTS + 1); // sampled arc, not a 2-point chord
+    expect(coords[0]).toEqual([9.1, 51.2]); // live start — exact endpoint
+    expect(coords[coords.length - 1]).toEqual([4.76, 52.31]); // EHAM — exact endpoint
+  });
+
+  it('returns an empty collection when the dest airport is missing from the dataset', () => {
+    expect(hoverTraceGeoJson({ lat: 0, lon: 0 }, 'ZZZZ', AIRPORTS)).toEqual({ type: 'FeatureCollection', features: [] });
+  });
+});
+
 describe('greatCircleArc (v0.12.2 — curved route traces)', () => {
   it('samples >2 points with the endpoints exactly at the airport coords', () => {
     const arc = greatCircleArc(AIRPORTS.get('EDDF')!, AIRPORTS.get('EHAM')!);