fix(vessels): hide the ridden ship's trail while its bridge is held

The sprite and card were hidden from the bridge but the selected-vessel
trail was not: at sea it ran astern from under the eye, and on a raised
river it lay buried under the water. It is now hidden while the bridge
holds its ship, keeping its history, and shown again on release.

src/layers/vessels/queries.js

@@ -563,6 +563,9 @@ export function createQueries({
       const next = normalizeSelectionMmsi(mmsi);
       if (state.cockpitSubjectMmsi === next) return true;
       state.cockpitSubjectMmsi = next;
+      // The ridden ship's trail runs from under the eye: hidden, its history
+      // kept, while the bridge holds the ship it belongs to.
+      state.trail?.setVisible?.(!next || next !== state.trailMmsi);
       components.rendering.updateVisibility(true);
       return true;
     },

src/layers/vessels/radarContacts.test.mjs

@@ -1,5 +1,6 @@
 // src/layers/vessels/radarContacts.test.mjs — the vessels the Cockpit bridge
-// radar draws: within range, nearest first, without the ship it rides.
+// radar draws: within range, nearest first, without the ship it rides; and
+// the ridden ship's own trail, hidden while the bridge holds it.
 import test from 'node:test';
 import assert from 'node:assert/strict';
 import { createVesselLayer } from './index.js';
@@ -128,6 +129,24 @@ test('ships with no MMSI each keep a key of their own', () => {
   assert.ok(ids.every((id) => id.startsWith('unkeyed:')));
 });
 
+test("the ridden ship's trail is hidden while the bridge holds it", () => {
+  const shown = [];
+  const trail = {
+    setPositions() {},
+    clear() {},
+    destroy() {},
+    setVisible: (visible) => shown.push(visible),
+  };
+  const layer = layerWith([record('own', 0), record('other', 2)], {
+    trail,
+    trailMmsi: 'own',
+  });
+  layer.setCockpitSubject('own');
+  assert.deepEqual(shown, [false]);
+  layer.setCockpitSubject(null);
+  assert.deepEqual(shown, [false, true]);
+});
+
 test('a disabled layer has no radar contacts', () => {
   const layer = layerWith([record('1', 1)], { enabled: false });
   assert.deepEqual(layer.getRadarContacts(54.5, 10.2, 6 * 1852), []);