CHANGELOG.md

@@ -1,5 +1,12 @@
 # Changelog
 
+## v0.22.0 — 2026-09-19 21:42
+- **Hover route trace on job-list rows (ISS-022).** Hovering an open package in the right pane now draws the ENTIRE great-circle trace between origin and destination, not just the two endpoint rings. Zero pane edits — the rows already sent `{kind:'package', originIcao, destIcao}`; `components/Map.tsx` now derives from/to for any hover target carrying two ICAOs and pushes a new pure builder's output (`hoverRouteGeoJson(fromIcao, toIcao, airportsByIcao)` in `lib/mapData.ts`: one LineString via the existing `greatCircleArc` slerp, empty FeatureCollection when either endpoint is missing from the airport index or the `''` no-hover sentinel) into a NEW dedicated `hover-routes` GeoJSON source + top-most dashed `hover-route` LineLayer (paint: `#facc15` matching the airports-highlight ring, width 4, `line-dasharray [2,2]`). The shared `routes` source can't carry this — it only holds FLYING legs, so an open package's or a grounded relocation's planned route was never in it. The layer is added in `ensureLayers` after the highlight layers so style switches keep it; `applyHoverRef` re-pushes data on every hover
+- **Same trace on On-board cargo rows (ISS-025).** Each `onboard-package-{id}` row in the left pane's On board section now reports `{kind:'package', originIcao, destIcao, planeId: plane.id}` on mouseenter — same full trace as job-list rows PLUS the carrying plane's halo stays lit via the new optional `planeId` field (Map uses `h.planeId ?? ''` for the planes/routes-highlight filters). Mouseleave restores the block's plain `{kind:'plane', id}` highlight; leaving the whole block still ends at null because React fires the child's mouseleave before the parent's
+- **Relocate panel hover previews the planned flight (ISS-027).** The left pane's Relocate section gains `data-testid="relocate-section"` + enter/leave handlers: with a grounded plane AND destination selected it reports `{kind:'route', fromIcao: relocatePlane.locationIcao, toIcao: relocateDest.icao}` (else null), and Map draws the planned trace AND rings ONLY the target airport in airports-highlight (origin stays unmarked — the destination is what the issue asks to see). `HoverTarget` (`components/hoverTypes.ts`) extends to `{kind:'plane';id} | {kind:'package';originIcao;destIcao;planeId?} | {kind:'route';fromIcao;toIcao}`. Existing semantics unchanged: plane hovers filter the three highlight layers exactly as before, package hovers keep BOTH endpoint rings (now plus the trace)
+- Tests: unit — new `describe('hoverRouteGeoJson …')` in `lib/mapData.test.ts`: no-hover sentinel → empty; two known airports → one arc with exact dataset endpoints; reversed-input symmetry; missing from/to ICAO → empty (baseline 283 → 288). e2e (`e2e/hover.spec.ts`) — open-package test extended with hover-route endpoint assertions (line geometry first/last coords compared against `/api/airports` lookups) + trace-clear check; new `hovering an on-board cargo row draws its trace and keeps the plane halo` (load via API, hover the row, assert trace endpoints + planes-highlight for that plane, abandon the package afterwards to leave a clean instance); new `hovering the Relocate section previews the planned route and target airport` (selects starter + LEMD via the existing testids, hovers `[data-testid="relocate-section"]`, asserts trace endpoints + target-only ring). New helpers: `airportLonLat(page, icao)` and `expectHoverRoute(page, fromIcao, toIcao)`; all new/extended assertions call `fitToAirports` first since `queryRenderedFeatures` is viewport-scoped
+- Verified: `tsc --noEmit` clean; unit suite green locally (288); `npx playwright test --list` = 41 tests (was 39, +2 new in hover.spec.ts); e2e not run locally by design — CI verifies against an isolated stack
+
 ## v0.21.0 — 2026-09-19 21:01
 - **Relocate panel moves to the left pane (ISS-023).** Flying an empty/grounded plane to another airport is "anything with our plane", so it belongs in the left pane, not as a market row on the right. The `.market-row.market-row-relocate` JSX (`relocate-plane` select of grounded planes labeled `{planeName} — {icao}`, `relocate-dest` name-sorted select, `relocate-go` button → `POST /api/planes/{id}/fly {destIcao}`) moved verbatim from `components/RightPane.tsx` into a new "Relocate" `<section>` in `components/LeftPane.tsx`, inserted between On board and Time. Its state (`relocatePlaneId` / `relocateDestIcao`) and the one-time `/api/airports` fetch (promise-ref pattern, GeoJSON → `{name, icao}[]` sorted by name) moved with it — the relocate-dest select was that fetch's only consumer in RightPane, so nothing else there changed. Busy gating rewired from RightPane's `busy` to LeftPane's own `useGameAction` instance (`actionsBusy`); a grounded-plane filter was added next to the existing `onboard` compute; plane labels reuse the expression already inlined in the Fleet rows. Testids kept byte-identical (`relocate-plane` / `relocate-dest` / `relocate-go`) and the row keeps its `.market-row market-row-relocate` classes (global CSS, works in the 360 px left pane); stale "280 px right pane" comment updated in `app/globals.css`. The map-popup relocation controls (`airport-popup-*`, Map.tsx) are a separate surface fed by the snapshot only — untouched
 - Tests: e2e — only `relocation.spec.ts` touches these testids and all locators are global, so no locator changes; the first test's title (which mentioned "right pane") and the file header comments now say left-pane Relocate section. No unit-test changes (baseline 283)

components/LeftPane.tsx

@@ -385,7 +385,17 @@ export default function LeftPane({ state, loading, error, onRefresh, applySnapsh
                     {cargo.map((pkg) => {
                       const penalty = abandonPenalty(pkg, clockMs);
                       return (
-                        <div key={pkg.id} data-testid={`onboard-package-${pkg.id}`} className="contract-row">
+                        // ISS-025 (v0.22.0): hovering a loaded package draws its full origin→dest trace on the map —
+                        // same as job-list rows — and keeps this plane's halo lit via planeId. Leaving the row restores
+                        // the block's plain plane highlight; leaving the whole block still ends at null (the child's
+                        // mouseleave fires before the parent's).
+                        <div
+                          key={pkg.id}
+                          data-testid={`onboard-package-${pkg.id}`}
+                          className="contract-row"
+                          onMouseEnter={() => onHover({ kind: 'package', originIcao: pkg.originIcao, destIcao: pkg.destIcao, planeId: plane.id })}
+                          onMouseLeave={() => onHover({ kind: 'plane', id: plane.id })}
+                        >
                           <button
                             type="button"
                             data-testid={`fly-to-${pkg.id}`}
@@ -438,7 +448,21 @@ export default function LeftPane({ state, loading, error, onRefresh, applySnapsh
 
           {/* ISS-023 (v0.21.0): moved here from the right-pane market row — it belongs with
               everything else about our planes, between On board and Time. */}
-          <section className="pane-section">
+          {/* ISS-027 (v0.22.0): hovering the section previews the planned relocation on the map —
+              dashed trace from the selected plane's airport to the destination + a ring on the target.
+              With no grounded plane or no loaded airport options there is nothing to preview → null. */}
+          <section
+            className="pane-section"
+            data-testid="relocate-section"
+            onMouseEnter={() =>
+              onHover(
+                relocatePlane && relocateDest
+                  ? { kind: 'route', fromIcao: relocatePlane.locationIcao, toIcao: relocateDest.icao }
+                  : null,
+              )
+            }
+            onMouseLeave={() => onHover(null)}
+          >
             <h3 className="pane-heading">Relocate</h3>
             {/* ISS-010 (v0.18.0): relocate a grounded plane — the fly endpoint already allows pure
                 repositioning, this row just exposes it for planes with nothing on board. */}

components/Map.tsx

@@ -8,7 +8,7 @@ import { DEFAULT_STYLE_ID, STYLES, STYLE_STORAGE_KEY, isStyleId, localAssetsAvai
 import type { GeoJsonFeatureCollection } from '../lib/airports';
 import type { StateSnapshot } from '../lib/game/state';
 import type { HoverTarget } from './hoverTypes';
-import { planesGeoJson, routesGeoJson, type AirportCoord, type PlaneFeatureProps } from '../lib/mapData';
+import { hoverRouteGeoJson, planesGeoJson, routesGeoJson, type AirportCoord, type PlaneFeatureProps } from '../lib/mapData';
 import { weatherFor } from '../lib/weather';
 import { approxLocalTime } from '../lib/localTime';
 
@@ -33,6 +33,11 @@ const ROUTES_LEGS_LAYER_ID = 'routes-legs';
 const PLANES_HIGHLIGHT_LAYER_ID = 'planes-highlight';
 const ROUTES_HIGHLIGHT_LAYER_ID = 'routes-highlight';
 const AIRPORTS_HIGHLIGHT_LAYER_ID = 'airports-highlight';
+// ISS-022/025/027 (v0.22.0): the hover route trace — its OWN source + top-most dashed line,
+// because the shared `routes` source only holds FLYING legs: an open package's or a grounded
+// relocation's planned route is never in it. applyHoverRef pushes data into it on every hover.
+const HOVER_ROUTES_SOURCE_ID = 'hover-routes';
+const HOVER_ROUTE_LAYER_ID = 'hover-route';
 
 function escapeHtml(s: string): string {
   return s.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;');
@@ -43,7 +48,8 @@ interface MapProps {
   // route lines. Null until the first successful poll.
   state?: StateSnapshot | null;
   // ISS-002 (v0.15.0): the side panels' hover target — highlights the matching plane
-  // (+ its route leg if flying) or a package's endpoint airports. Null = nothing hovered.
+  // (+ its route leg if flying) or a package's endpoint airports, and (ISS-022/025/027 v0.22.0)
+  // draws the full great-circle trace between any hovered target's two endpoints. Null = nothing hovered.
   hovered?: HoverTarget | null;
   // ISS-010 (v0.18.0): push an action endpoint's full response snapshot into the shared
   // shell state — same callback RightPane receives, used by the airport popup's Relocate row.
@@ -101,16 +107,39 @@ export default function FlightMap({ state, hovered, applySnapshot }: MapProps) {
     const map = mapRef.current;
     if (!map) return;
     const h = hoveredRef.current;
-    // The empty-string sentinel matches nothing: no feature has id/icao ''.
-    const planeId = h && h.kind === 'plane' ? h.id : '';
+    // The empty-string sentinel matches nothing: no feature has id/icao ''. A package hover may
+    // name its plane (ISS-025 on-board cargo rows), so that plane's halo stays lit too.
+    let planeId = '';
+    let fromIcao = '';
+    let toIcao = '';
+    if (h) {
+      if (h.kind === 'plane') planeId = h.id;
+      else if (h.kind === 'package') {
+        planeId = h.planeId ?? '';
+        fromIcao = h.originIcao;
+        toIcao = h.destIcao;
+      } else {
+        // 'route' — the Relocate panel's planned flight: trace + target airport only.
+        fromIcao = h.fromIcao;
+        toIcao = h.toIcao;
+      }
+    }
     if (map.getLayer(PLANES_HIGHLIGHT_LAYER_ID)) {
       map.setFilter(PLANES_HIGHLIGHT_LAYER_ID, ['==', ['get', 'id'], planeId]);
     }
     if (map.getLayer(ROUTES_HIGHLIGHT_LAYER_ID)) {
       map.setFilter(ROUTES_HIGHLIGHT_LAYER_ID, ['==', ['get', 'planeId'], planeId]);
     }
-    const originIcao = h && h.kind === 'package' ? h.originIcao : '';
-    const destIcao = h && h.kind === 'package' ? h.destIcao : '';
+    // ISS-022/025/027: the hover route trace — one great-circle line for any target carrying two
+    // ICAOs (package origin→dest / relocate fromIcao→toIcao); empty when either endpoint is unknown.
+    const hoverSource = map.getSource(HOVER_ROUTES_SOURCE_ID) as maplibregl.GeoJSONSource | undefined;
+    if (hoverSource) {
+      void hoverSource.setData(hoverRouteGeoJson(fromIcao, toIcao, airportsIndexRef.current ?? new Map()));
+    }
+    // Package hovers ring BOTH endpoints (v0.15.0 behavior); 'route' hovers ring the TARGET only —
+    // the relocation's destination is what ISS-027 asks to see. Plane hovers ring nothing.
+    const originIcao = h?.kind === 'package' ? fromIcao : '';
+    const destIcao = h?.kind === 'package' || h?.kind === 'route' ? toIcao : '';
     if (map.getLayer(AIRPORTS_HIGHLIGHT_LAYER_ID)) {
       map.setFilter(
         AIRPORTS_HIGHLIGHT_LAYER_ID,
@@ -384,6 +413,24 @@ export default function FlightMap({ state, hovered, applySnapshot }: MapProps) {
             },
           });
         }
+        // ISS-022/025/027 (v0.22.0): the hover route trace — added LAST so it sits above every
+        // other layer, including the highlight rings at its endpoints. Own source: the shared
+        // `routes` source only holds flying legs, never a planned one. Empty until a hover sets data.
+        if (!map.getSource(HOVER_ROUTES_SOURCE_ID)) {
+          map.addSource(HOVER_ROUTES_SOURCE_ID, { type: 'geojson', data: { type: 'FeatureCollection', features: [] } });
+        }
+        if (!map.getLayer(HOVER_ROUTE_LAYER_ID)) {
+          map.addLayer({
+            id: HOVER_ROUTE_LAYER_ID,
+            type: 'line',
+            source: HOVER_ROUTES_SOURCE_ID,
+            paint: {
+              'line-color': '#facc15', // matches the airports-highlight ring — one "trace" color
+              'line-width': 4,
+              'line-dasharray': [2, 2], // dashed = planned route, distinct from solid flying legs
+            },
+          });
+        }
         // Layer-scoped listeners survive setStyle (they filter by layer id at event
         // time), so off+on with the same reference re-wires without duplicating.
         map.off('click', AIRPORTS_LAYER_ID, onAirportClick);

components/hoverTypes.ts

@@ -1,7 +1,12 @@
 // ISS-002 — what a side-panel hover highlights on the map (v0.15.0): a plane marker
 // (+ its route leg if flying) or both endpoint airports of an open package. The shell
 // owns this state and passes it to <Map>; panes report it via their onHover callback.
+// ISS-022/025/027 (v0.22.0): any target carrying two ICAOs also makes the map draw the full
+// great-circle trace between them — package hovers carry origin→dest, 'route' hovers (the
+// Relocate panel) carry fromIcao→toIcao; a package hover may additionally name its plane so
+// that plane's halo stays lit alongside the trace.
 
 export type HoverTarget =
   | { kind: 'plane'; id: string }
-  | { kind: 'package'; originIcao: string; destIcao: string };
+  | { kind: 'package'; originIcao: string; destIcao: string; planeId?: string }
+  | { kind: 'route'; fromIcao: string; toIcao: string };

e2e/hover.spec.ts

@@ -6,6 +6,9 @@ import { test, expect, type Page } from '@playwright/test';
 // highlight layers (planes-highlight / routes-highlight / airports-highlight), each filtered
 // to match nothing until a hover sets the filter — asserted here via window.__flightMap's
 // queryRenderedFeatures, same pattern as e2e/map.spec.ts and e2e/map-interactions.spec.ts.
+// ISS-022/025/027 (v0.22.0): any hover carrying two endpoints ALSO draws the full great-circle
+// trace between them in a fourth top-most layer (`hover-route`, dashed) — job-list rows, on-board
+// cargo rows and the Relocate section; the relocate preview rings only its TARGET airport.
 
 const SCALE = 1000; // fastest sim speed (v0.14.0 ladder top) — keeps flights to seconds of real time
 const HUB = 'EDDF'; // must match HUB_ICAO in lib/game/seed.ts
@@ -160,6 +163,35 @@ async function fitToAirports(page: Page, icaos: string[]): Promise<void> {
   await page.waitForTimeout(300);
 }
 
+// [lon, lat] of an airport from the same /api/airports dataset the map draws its traces from.
+async function airportLonLat(page: Page, icao: string): Promise<[number, number]> {
+  const fc = (await (await page.request.get('/api/airports')).json()) as {
+    features: Array<{ properties: { icao: string; lat: number; lon: number } }>;
+  };
+  const f = fc.features.find((x) => x.properties.icao === icao);
+  if (!f) throw new Error(`airport ${icao} not found in /api/airports`);
+  return [f.properties.lon, f.properties.lat];
+}
+
+// ISS-022/025/027: the hover-route layer must hold exactly one LineString whose first and last
+// coordinates are the two airports' exact dataset coords (greatCircleArc returns them verbatim
+// at t=0/t=1, so strict equality is safe). Call fitToAirports([from, to]) first — rendered
+// features are viewport-scoped.
+async function expectHoverRoute(page: Page, fromIcao: string, toIcao: string): Promise<void> {
+  const [from, to] = await Promise.all([airportLonLat(page, fromIcao), airportLonLat(page, toIcao)]);
+  await expect.poll(async () => {
+    const feats = (await renderedFeatures(page, ['hover-route'])) as Array<{ geometry: { coordinates: [number, number][] } }>;
+    if (feats.length !== 1) return false;
+    const coords = feats[0].geometry.coordinates;
+    return (
+      coords[0][0] === from[0] &&
+      coords[0][1] === from[1] &&
+      coords[coords.length - 1][0] === to[0] &&
+      coords[coords.length - 1][1] === to[1]
+    );
+  }, { timeout: 15_000, message: `waiting for the hover-route line ${fromIcao} → ${toIcao}` }).toBe(true);
+}
+
 test('hovering a fleet row highlights the plane on the map', async ({ page }) => {
   test.setTimeout(300_000); // self-heal can take minutes after an interrupted run
   await flyHomeViaApi(page); // deterministic: the starter sits at EDDF, inside the initial view
@@ -238,11 +270,107 @@ test('hovering an open package highlights its endpoint airports', async ({ page
   }, { timeout: 15_000, message: 'waiting for the airports-highlight layer to show both endpoints' })
     .toBe(JSON.stringify([HUB, DEST].sort()));
 
+  // ISS-022 (v0.22.0): the ENTIRE trace is drawn too — a great-circle line from origin to dest,
+  // not just the endpoint rings.
+  await expectHoverRoute(page, HUB, DEST);
+
   await unhover(page);
   await expect.poll(async () => (await renderedFeatures(page, ['airports-highlight'])).length, {
     timeout: 15_000,
     message: 'waiting for the highlight to clear after mouseleave',
   }).toBe(0);
+  await expect.poll(async () => (await renderedFeatures(page, ['hover-route'])).length, {
+    timeout: 15_000,
+    message: 'waiting for the hover route trace to clear after mouseleave',
+  }).toBe(0);
+});
+
+test('hovering an on-board cargo row draws its trace and keeps the plane halo', async ({ page }) => {
+  test.setTimeout(300_000); // self-heal can take minutes after an interrupted run
+  await flyHomeViaApi(page); // deterministic: the starter sits grounded at EDDF
+
+  // Load a package onto the grounded starter so it shows up in the On board section.
+  const pkg = await createPackage(page, HUB, DEST);
+  const load = await page.request.post(`/api/packages/${pkg.id}/load`, { data: { planeId: 'plane-starter' } });
+  expect(load.status()).toBe(200);
+
+  await page.goto('/');
+  await waitForAirportCount(page);
+
+  const row = page.locator(`[data-testid="onboard-package-${pkg.id}"]`);
+  await expect(row, 'the loaded package appears in the On board section').toBeVisible({ timeout: 15_000 });
+
+  // Both endpoints must be in-viewport for queryRenderedFeatures to see the trace.
+  await fitToAirports(page, [HUB, DEST]);
+
+  await row.hover();
+  // ISS-025 (v0.22.0): same full origin→dest trace as job-list rows…
+  await expectHoverRoute(page, HUB, DEST);
+  // …and the package's plane keeps its halo lit (the hover carries planeId).
+  await expect.poll(async () => {
+    const feats = (await renderedFeatures(page, ['planes-highlight'])) as Array<{ properties: Record<string, unknown> }>;
+    return feats.length > 0 && feats[0].properties.id === 'plane-starter';
+  }, { timeout: 15_000, message: 'waiting for the planes-highlight layer to show plane-starter' }).toBe(true);
+
+  await unhover(page);
+  await expect.poll(async () => (await renderedFeatures(page, ['hover-route'])).length, {
+    timeout: 15_000,
+    message: 'waiting for the hover route trace to clear after mouseleave',
+  }).toBe(0);
+  await expect.poll(async () => (await renderedFeatures(page, ['planes-highlight'])).length, {
+    timeout: 15_000,
+    message: 'waiting for the highlight to clear after mouseleave',
+  }).toBe(0);
+
+  // Leave the instance clean: abandon the loaded package so later specs start with an empty starter.
+  const res = await page.request.post(`/api/packages/${pkg.id}/abandon`);
+  expect(res.status()).toBe(200);
+});
+
+test('hovering the Relocate section previews the planned route and target airport', async ({ page }) => {
+  test.setTimeout(300_000); // self-heal can take minutes after an interrupted run
+  await flyHomeViaApi(page); // deterministic: the starter sits grounded at EDDF
+
+  await page.goto('/');
+  await waitForAirportCount(page);
+
+  const section = page.getByTestId('relocate-section');
+  await expect(section, 'the Relocate section is visible').toBeVisible({ timeout: 15_000 });
+
+  // LeftPane fetches /api/airports on its own (separate from the map header count) — wait for
+  // the destination options to populate before selecting.
+  await expect(page.getByTestId('relocate-dest').locator(`option[value="${DEST}"]`)).toHaveCount(1, { timeout: 15_000 });
+
+  // Pick the starter + a known destination explicitly (the effective-selection defaults already do this).
+  await page.getByTestId('relocate-plane').selectOption('plane-starter');
+  await page.getByTestId('relocate-dest').selectOption(DEST);
+
+  // Both endpoints must be in-viewport for queryRenderedFeatures to see the trace.
+  await fitToAirports(page, [HUB, DEST]);
+
+  expect(await renderedFeatures(page, ['hover-route'])).toHaveLength(0);
+  expect(await renderedFeatures(page, ['airports-highlight'])).toHaveLength(0);
+
+  // ISS-027 (v0.22.0): hovering the panel with a plane + destination selected previews the flight —
+  // dashed trace from the plane's airport to the destination…
+  await section.hover();
+  await expectHoverRoute(page, HUB, DEST);
+  // …and rings ONLY the target airport (the origin stays unmarked).
+  await expect.poll(async () => {
+    const feats = (await renderedFeatures(page, ['airports-highlight'])) as Array<{ properties: Record<string, unknown> }>;
+    return JSON.stringify(feats.map((f) => f.properties.icao).sort());
+  }, { timeout: 15_000, message: 'waiting for the airports-highlight layer to ring only the target' })
+    .toBe(JSON.stringify([DEST]));
+
+  await unhover(page);
+  await expect.poll(async () => (await renderedFeatures(page, ['hover-route'])).length, {
+    timeout: 15_000,
+    message: 'waiting for the hover route trace to clear after mouseleave',
+  }).toBe(0);
+  await expect.poll(async () => (await renderedFeatures(page, ['airports-highlight'])).length, {
+    timeout: 15_000,
+    message: 'waiting for the highlight to clear after mouseleave',
+  }).toBe(0);
 });
 
 test('hovering an on-board block of a flying plane highlights its route', async ({ page }) => {

lib/mapData.test.ts

@@ -1,6 +1,6 @@
 import { describe, expect, it } from 'vitest';
 import type { StateSnapshot } from './game/state';
-import { planesGeoJson, routesGeoJson, greatCircleArc, ROUTE_ARC_SEGMENTS, type AirportCoord } from './mapData';
+import { planesGeoJson, routesGeoJson, hoverRouteGeoJson, greatCircleArc, ROUTE_ARC_SEGMENTS, type AirportCoord } from './mapData';
 import { haversineKm } from './geo';
 
 const AIRPORTS = new Map<string, AirportCoord>([
@@ -140,6 +140,42 @@ describe('routesGeoJson (v0.12.0 — one line per flying plane\'s current leg)',
   });
 });
 
+describe('hoverRouteGeoJson (ISS-022/025/027 v0.22.0 — hover route trace)', () => {
+  it('returns an empty collection for the no-hover "" sentinel', () => {
+    expect(hoverRouteGeoJson('', '', AIRPORTS)).toEqual({ type: 'FeatureCollection', features: [] });
+  });
+
+  it('draws one great-circle line between two known airports with exact endpoints', () => {
+    const fc = hoverRouteGeoJson('EDDF', '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([8.56, 50.03]); // EDDF [lon, lat] — exact endpoint
+    expect(coords[coords.length - 1]).toEqual([4.76, 52.31]); // EHAM — exact endpoint
+  });
+
+  it('draws the same trace reversed (endpoints swapped, arc mirrored)', () => {
+    const ab = hoverRouteGeoJson('EDDF', 'EHAM', AIRPORTS).features[0].geometry.coordinates;
+    const ba = hoverRouteGeoJson('EHAM', 'EDDF', AIRPORTS).features[0].geometry.coordinates;
+    expect(ba.length).toBe(ab.length);
+    // The slerp is symmetric up to floating-point rounding (1 − t ≠ (N−t)/N bit-exactly), so
+    // compare with a tolerance: each reversed point sits on the forward arc within ~1e-9 degrees.
+    for (let i = 0; i < ab.length; i++) {
+      expect(Math.abs(ba[i][0] - ab[ab.length - 1 - i][0])).toBeLessThan(1e-9);
+      expect(Math.abs(ba[i][1] - ab[ab.length - 1 - i][1])).toBeLessThan(1e-9);
+    }
+  });
+
+  it('returns an empty collection when the from airport is missing from the dataset', () => {
+    expect(hoverRouteGeoJson('ZZZZ', 'EDDV', AIRPORTS)).toEqual({ type: 'FeatureCollection', features: [] });
+  });
+
+  it('returns an empty collection when the to airport is missing from the dataset', () => {
+    expect(hoverRouteGeoJson('EDDF', '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')!);

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "flight-ops",
-  "version": "0.21.0",
+  "version": "0.22.0",
   "private": true,
   "scripts": {
     "dev": "next dev -p 3000",