fix(street-level): budgeted mesh sampling, in-place cones, date line, horizon

From the IC8 review of #768, each with tests that fail before:

- P1: a mesh batch no longer rebuilds the selected sequence's cones. The
  drawn cones are indexed by mesh cell; a batch that touches none of them
  is ignored and the affected cones are moved in place (no removeAll/add).
- P2: mesh sampling keeps to its 6 ms slices. Requests are taken in inside
  the budget, only cells within range of the camera are queued, the queue
  is a persistent min-heap re-ranked in one pass only after a 100 m camera
  move, and the deadline starts before any work. Coverage keeps a bounding
  box per line and densifies a line only once it comes within range. On a
  synthetic dense tile (600 x 40 points): slice median ~10 ms -> 5 ms, max
  18-30 ms -> 6.7 ms, refresh cost 11-24 ms -> 1.5-3 ms.
- P2: image cones and the photo marker are horizon-culled like the
  overview dots (one createHorizonCull in view.js, shared by all three).
- P2: a selection change recolours the previous zoom's lines still on
  screen and the old lines a cast swap keeps showing.
- P2: distances (metresBetween), line densification and ground-corner
  requests go the short way round +-180 deg (wrapLon in tileMath.js), so
  nearest ordering, cone thinning, mesh range and cast lines are right
  across the date line.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/layers/streetLevel/marker.test.mjs

@@ -0,0 +1,78 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import * as Cesium from 'cesium';
+import { createMarker } from './marker.js';
+
+// The marker glyph draws on a canvas; Node has none, so drawing is a no-op.
+const noop = () => {};
+const context2d = new Proxy({}, { get: () => noop, set: () => true });
+globalThis.document ??= {
+  createElement: () => ({ getContext: () => context2d }),
+};
+
+/** A viewer whose camera is 20,000 km over `view`, and its pre-render listeners. */
+function setup() {
+  const view = { lon: -121.49, lat: 38.58, height: 20_000_000 };
+  const preRender = new Set();
+  const viewer = {
+    camera: {
+      get positionWC() {
+        return Cesium.Cartesian3.fromDegrees(view.lon, view.lat, view.height);
+      },
+    },
+    scene: {
+      primitives: { add: (p) => p, remove() {} },
+      preRender: {
+        addEventListener(listener) {
+          preRender.add(listener);
+          return () => preRender.delete(listener);
+        },
+      },
+    },
+  };
+  const state = {
+    services: {},
+    viewer,
+    surface: 'draped',
+    marker: {
+      // Stands in for the billboard collection; ensure() keeps it.
+      collection: {
+        show: true,
+        add: (options) => ({ ...options }),
+        removeAll() {},
+      },
+      billboard: null,
+    },
+  };
+  const marker = createMarker({ state, parts: {} });
+  const frame = () => {
+    for (const listener of [...preRender]) listener();
+  };
+  return { state, view, preRender, marker, frame };
+}
+
+test('the photo marker is hidden behind the globe, and shows from its side (review IC8 P2)', () => {
+  const { state, view, preRender, marker, frame } = setup();
+  // Placed on the far side of the Earth from the camera.
+  marker.set({ lon: 58.51, lat: -38.58 }, 90);
+  const billboard = state.marker.billboard;
+  assert.equal(billboard.show, false, 'not drawn through the globe');
+  // Fly round to its side: it shows.
+  view.lon = 58.51;
+  view.lat = -38.58;
+  frame();
+  assert.equal(billboard.show, true);
+  // Moved to the far side again, without the camera moving.
+  marker.set({ lon: -121.49, lat: 38.58 }, 0);
+  assert.equal(billboard.show, false, 'culled where it now stands');
+  marker.clear();
+  assert.equal(preRender.size, 0, 'the cull listener is gone');
+});
+
+test('destroying the marker stops the horizon cull', () => {
+  const { marker, preRender } = setup();
+  marker.set({ lon: -121.49, lat: 38.58 }, 0);
+  assert.equal(preRender.size, 1);
+  marker.destroy();
+  assert.equal(preRender.size, 0);
+});