Merge current main into HAL-522 review candidate

src/app/layers/streetLevel.js

@@ -1,6 +1,7 @@
 import { createStreetLevelLayer } from '../../layers/streetLevel/index.js';
 import { createMapillaryProvider } from '../../layers/streetLevel/providers/mapillary/index.js';
 import { createGoogleProvider } from '../../layers/streetLevel/providers/google/index.js';
+import { createKartaViewProvider } from '../../layers/streetLevel/providers/kartaview/index.js';
 import * as sprites from '../../data/spriteOrder.js';
 import * as picking from '../../data/pickRegistry.js';
 import * as input from '../../data/inputOwnership.js';
@@ -10,12 +11,16 @@ import * as render from '../../renderGovernor.js';
 /** The browser Maps key the scene was started with (src/app/scene.js). */
 const googleApiKey = () => globalThis.window?.__GOOGLE_MAPS_API_KEY__ || null;
 
-/** Mapillary and Google Street View, once the Mapillary source is supplied; else none. */
+/**
+ * Mapillary, Google Street View and KartaView, once the Mapillary source is
+ * supplied; else none.
+ */
 function defaultProviders(sources) {
   if (sources.mapillary == null) return [];
   return [
     createMapillaryProvider({ source: sources.mapillary }),
     createGoogleProvider({ getApiKey: googleApiKey }),
+    createKartaViewProvider(),
   ];
 }
 

src/app/layers/streetLevel.test.mjs

@@ -28,7 +28,7 @@ test('explicit providers replace the default source and an empty list removes it
   );
 });
 
-test('the defaults are Mapillary (given its source) and Street View, which starts off and travels as a provider switch', async () => {
+test('the defaults are Mapillary (given its source), Street View and KartaView, which start off and travel as provider switches', async () => {
   const { createDefaultLayerState } = await import('../../data/layerState.js');
   const mapillary = {
     getStatus() {},
@@ -37,7 +37,7 @@ test('the defaults are Mapillary (given its source) and Street View, which start
     nearestImages() {},
   };
   const layer = createApplicationStreetLevel({ sources: { mapillary } });
-  assert.deepEqual(layer.providerIds, ['mapillary', 'google']);
+  assert.deepEqual(layer.providerIds, ['mapillary', 'google', 'kartaview']);
   // A fresh page and a restored default agree: Street View is billed, so off.
   layer.setParams(createDefaultLayerState().options['street-level']);
   assert.equal(layer.getParams().google, false);
@@ -45,7 +45,12 @@ test('the defaults are Mapillary (given its source) and Street View, which start
   // A link that lit Street View carries it in the shared switch field.
   layer.setParams({ providerSwitches: 'google-1' });
   assert.equal(layer.getParams().google, true);
-  assert.equal(layer.getParams().providerSwitches, 'google-1');
+  assert.equal(layer.getParams().providerSwitches, 'google-1*kartaview-0');
+  // KartaView is keyless and free, but one source shows at a time.
+  layer.setParams({ providerSwitches: 'kartaview-1' });
+  assert.equal(layer.getParams().kartaview, true);
+  assert.equal(layer.getParams().google, false);
+  assert.equal(layer.getParams().mapillary, false);
   // Without the application's Street Level source there are none.
   assert.deepEqual(createApplicationStreetLevel({}).providerIds, []);
 });

src/data/cctvNyc.test.mjs

@@ -0,0 +1,391 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+
+import {
+  loadNycSourcesFromOpenData,
+  nycCameraIsOnline,
+  nycCameraName,
+  nycCameraToSource,
+} from '../../server/providers/cctv/sources.js';
+import {
+  DEFAULT_CCTV_MAX_SOURCES,
+  DEFAULT_NYC_MAX_SOURCES,
+  NYC_CAMERAS_URL,
+  NYC_GROUND_ELEVATION_M,
+  NYC_IMAGE_ORIGIN,
+  NYC_IMAGE_URL,
+  NYC_MAX_CATALOG_BYTES,
+} from '../../server/providers/cctv/constants.js';
+import {
+  CAMERA_CODE_MAX_CHARS,
+  isLikelyNycCoordinate,
+} from '../../server/providers/cctv/normalize.js';
+import { createCctvCatalog } from '../../server/providers/cctv/catalog.js';
+
+/**
+ * A response whose body is a live stream, plus a flag that flips when the
+ * stream is cancelled. A rejection path that returns without cancelling holds
+ * the transport open, so the flag is what the refusal tests actually assert.
+ */
+const streamingResponse = (init = {}) => {
+  const state = { cancelled: false };
+  const body = new ReadableStream({
+    start(controller) {
+      controller.enqueue(new TextEncoder().encode('['));
+    },
+    cancel() {
+      state.cancelled = true;
+    },
+  });
+  return { response: new Response(body, init), state };
+};
+
+const MIDTOWN_ID = '8a6bc417-4877-4ebe-8052-88c1b261baf1';
+const BROOKLYN_ID = '11111111-2222-3333-4444-555555555555';
+
+/** One TMC camera row, shaped like the live `webcams.nyctmc.org` payload. */
+const row = (overrides = {}) => ({
+  id: MIDTOWN_ID,
+  name: 'Central Park West @ 86 St',
+  latitude: 40.785302,
+  longitude: -73.969353,
+  area: 'Manhattan',
+  isOnline: 'true',
+  imageUrl: NYC_IMAGE_URL(MIDTOWN_ID),
+  ...overrides,
+});
+
+test('a NYC row maps to a source on the pinned HTTPS frame host', () => {
+  const source = nycCameraToSource(row());
+  assert.equal(source.id, `nyc-${MIDTOWN_ID}`);
+  assert.equal(source.name, 'Central Park West @ 86 St');
+  assert.equal(source.city, 'Manhattan');
+  assert.equal(source.cityId, 'nyc');
+  assert.equal(source.provider, 'NYC DOT Traffic Management Center');
+  assert.equal(source.lat, 40.785302);
+  assert.equal(source.lon, -73.969353);
+  assert.equal(source.feedType, 'image');
+  assert.equal(source.sourceKind, 'nyc-dot-tmc');
+  assert.equal(
+    source.license,
+    'Public NYC DOT Traffic Management Center traffic camera',
+  );
+  assert.equal(source.groundElevationM, NYC_GROUND_ELEVATION_M);
+  assert.equal(source.url, NYC_IMAGE_URL(MIDTOWN_ID));
+  assert.equal(source.url, source.snapshotUrl);
+  assert.ok(source.url.startsWith(NYC_IMAGE_ORIGIN));
+  assert.equal(source.headingConfidence, 'low');
+  assert.ok(Number.isFinite(source.headingDeg));
+});
+
+test('frame URLs are synthesized from the UUID; the payload URL is ignored', () => {
+  const source = nycCameraToSource(
+    row({ imageUrl: 'https://evil.example/cameras/x/image' }),
+  );
+  assert.equal(source.url, NYC_IMAGE_URL(MIDTOWN_ID));
+  assert.equal(source.snapshotUrl, source.url);
+});
+
+test('offline cameras, off-city geometry and unusable ids are dropped', () => {
+  assert.equal(nycCameraToSource(row({ isOnline: 'false' })), null);
+  assert.equal(nycCameraToSource(row({ isOnline: false })), null);
+  assert.equal(
+    nycCameraToSource(row({ isOnline: 'TRUE' })).id,
+    `nyc-${MIDTOWN_ID}`,
+  );
+  assert.equal(
+    nycCameraToSource(row({ isOnline: true })).id,
+    `nyc-${MIDTOWN_ID}`,
+  );
+  // Austin: a plausible lat/lon, but not a New York camera.
+  assert.equal(
+    nycCameraToSource(row({ latitude: 30.2672, longitude: -97.7431 })),
+    null,
+  );
+  assert.equal(nycCameraToSource(row({ latitude: 0, longitude: 0 })), null);
+  assert.equal(nycCameraToSource(row({ id: '../etc/passwd' })), null);
+  assert.equal(nycCameraToSource(row({ id: 'not-a-uuid' })), null);
+  assert.equal(nycCameraToSource(row({ id: `${MIDTOWN_ID}/../x` })), null);
+  assert.equal(nycCameraToSource(null), null);
+});
+
+test('ids lower-case the UUID and unknown boroughs fall back to New York', () => {
+  const mixed = nycCameraToSource(
+    row({ id: MIDTOWN_ID.toUpperCase(), area: 'Long Island' }),
+  );
+  assert.equal(mixed.id, `nyc-${MIDTOWN_ID}`);
+  assert.equal(mixed.city, 'New York');
+  assert.equal(
+    mixed.url,
+    NYC_IMAGE_URL(MIDTOWN_ID.toUpperCase()),
+    'the registered frame path keeps the catalog UUID spelling',
+  );
+});
+
+test('a nameless row still gets a label', () => {
+  assert.equal(
+    nycCameraName({ name: '  FDR Drive @ 23 St ' }, 'nyc-x'),
+    'FDR Drive @ 23 St',
+  );
+  assert.equal(nycCameraName({}, `nyc-${MIDTOWN_ID}`), 'NYC Camera 8a6bc417');
+  assert.equal(nycCameraIsOnline('true'), true);
+  assert.equal(nycCameraIsOnline('false'), false);
+});
+
+test('the unselected label is the intersection, trimmed to the code width', () => {
+  assert.equal(nycCameraToSource(row()).code, 'CENTRAL PARK WEST @ 86 ST');
+  const long = nycCameraToSource(
+    row({
+      name: 'Brooklyn Queens Expressway @ Atlantic Avenue / Flatbush Avenue Extension',
+    }),
+  );
+  assert.ok(long.code.length <= CAMERA_CODE_MAX_CHARS);
+  assert.ok(long.code.endsWith('…'));
+  assert.ok(long.code.startsWith('BROOKLYN'));
+});
+
+test('the loader reads the keyless catalog and collapses duplicate ids', async (t) => {
+  t.mock.method(console, 'log', () => {});
+  const requested = [];
+  t.mock.method(globalThis, 'fetch', async (url, init) => {
+    requested.push([String(url), init.redirect]);
+    return Response.json([
+      row({ latitude: 40.758, longitude: -73.9855 }),
+      row({
+        name: 'Central Park West @ 86 St (duplicate)',
+        latitude: 40.758,
+        longitude: -73.9855,
+      }),
+      row({
+        id: BROOKLYN_ID,
+        name: 'Atlantic Ave @ Flatbush Ave',
+        latitude: 40.65,
+        longitude: -73.96,
+        area: 'Brooklyn',
+        imageUrl: NYC_IMAGE_URL(BROOKLYN_ID),
+      }),
+      row({ isOnline: 'false', name: 'Offline camera' }),
+      row({ id: 'https://evil.example/x' }),
+    ]);
+  });
+  const cameras = await loadNycSourcesFromOpenData();
+  assert.deepEqual(requested, [[NYC_CAMERAS_URL, 'manual']]);
+  assert.deepEqual(
+    cameras.map((camera) => camera.id),
+    // Nearest to a borough anchor first: the Times Square camera before Brooklyn.
+    [`nyc-${MIDTOWN_ID}`, `nyc-${BROOKLYN_ID}`],
+  );
+  assert.equal(cameras[0].name, 'Central Park West @ 86 St');
+  assert.equal(cameras[1].city, 'Brooklyn');
+});
+
+test('an upstream failure yields an empty pack and releases the response', async (t) => {
+  t.mock.method(console, 'warn', () => {});
+  const failed = streamingResponse({ status: 503 });
+  t.mock.method(globalThis, 'fetch', async () => failed.response);
+  assert.deepEqual(await loadNycSourcesFromOpenData(), []);
+  assert.equal(failed.state.cancelled, true, 'the failed body is cancelled');
+
+  t.mock.restoreAll();
+  t.mock.method(console, 'warn', () => {});
+  t.mock.method(globalThis, 'fetch', async () => {
+    throw new Error('network down');
+  });
+  assert.deepEqual(await loadNycSourcesFromOpenData(), []);
+});
+
+test('the catalog fetch refuses redirects and oversized bodies', async (t) => {
+  t.mock.method(console, 'warn', () => {});
+  const seen = [];
+  const redirected = streamingResponse({
+    status: 302,
+    headers: { location: 'https://evil.example/cameras.json' },
+  });
+  t.mock.method(globalThis, 'fetch', async (url, init) => {
+    seen.push([String(url), init.redirect]);
+    return redirected.response;
+  });
+  assert.deepEqual(await loadNycSourcesFromOpenData(), []);
+  assert.deepEqual(seen, [[NYC_CAMERAS_URL, 'manual']]);
+  assert.equal(
+    redirected.state.cancelled,
+    true,
+    'the redirect body is cancelled',
+  );
+
+  t.mock.restoreAll();
+  t.mock.method(console, 'warn', () => {});
+  t.mock.method(globalThis, 'fetch', async () => {
+    const body = JSON.stringify([row()]);
+    return new Response(body, {
+      headers: {
+        'Content-Type': 'application/json',
+        'content-length': String(NYC_MAX_CATALOG_BYTES + 1),
+      },
+    });
+  });
+  assert.deepEqual(await loadNycSourcesFromOpenData(), []);
+
+  t.mock.restoreAll();
+  t.mock.method(console, 'warn', () => {});
+  t.mock.method(globalThis, 'fetch', async () => {
+    const oversized = 'x'.repeat(NYC_MAX_CATALOG_BYTES + 1024);
+    return new Response(
+      new ReadableStream({
+        start(controller) {
+          controller.enqueue(new TextEncoder().encode(oversized));
+          controller.close();
+        },
+      }),
+      { headers: { 'Content-Type': 'application/json' } },
+    );
+  });
+  assert.deepEqual(await loadNycSourcesFromOpenData(), []);
+});
+
+test('a reduced pack cap keeps cameras nearest the borough anchors', async (t) => {
+  t.mock.method(console, 'log', () => {});
+  const saved = process.env.CCTV_NYC_MAX_SOURCES;
+  t.after(() => {
+    if (saved === undefined) delete process.env.CCTV_NYC_MAX_SOURCES;
+    else process.env.CCTV_NYC_MAX_SOURCES = saved;
+  });
+  process.env.CCTV_NYC_MAX_SOURCES = '8';
+  const rows = [
+    // Far southern Staten Island, listed first so only distance can keep them.
+    ...[40.5, 40.505, 40.51, 40.515, 40.52, 40.525].map((lat, i) =>
+      row({
+        id: `aaaaaaaa-bbbb-cccc-dddd-${String(i).padStart(12, '0')}`,
+        latitude: lat,
+        longitude: -74.24,
+        area: 'Staten Island',
+        name: `SI ${i}`,
+      }),
+    ),
+    ...[40.758, 40.757, 40.756, 40.755, 40.754, 40.753].map((lat, i) =>
+      row({
+        id: `bbbbbbbb-cccc-dddd-eeee-${String(i).padStart(12, '0')}`,
+        latitude: lat,
+        longitude: -73.9855,
+        area: 'Manhattan',
+        name: `Midtown ${i}`,
+      }),
+    ),
+  ];
+  t.mock.method(globalThis, 'fetch', async () => Response.json(rows));
+  const cameras = await loadNycSourcesFromOpenData();
+  assert.equal(cameras.length, 8);
+  assert.deepEqual(
+    cameras.map((camera) => camera.city),
+    [
+      'Manhattan',
+      'Manhattan',
+      'Manhattan',
+      'Manhattan',
+      'Manhattan',
+      'Manhattan',
+      'Staten Island',
+      'Staten Island',
+    ],
+    'Midtown fills first; the Staten Island anchor still keeps a share',
+  );
+});
+
+/**
+ * Serve the NYC catalog to the NYC endpoint and an empty payload to every
+ * other pack, so one catalog refresh exercises the registration without
+ * reaching the network.
+ */
+const runCatalogWithMockedUpstreams = async (t) => {
+  const requested = [];
+  t.mock.method(console, 'log', () => {});
+  t.mock.method(console, 'warn', () => {});
+  t.mock.method(globalThis, 'fetch', async (url) => {
+    const href = String(url);
+    requested.push(href);
+    if (href === NYC_CAMERAS_URL) {
+      return Response.json([
+        row({ latitude: 40.758, longitude: -73.9855 }),
+        row({
+          id: BROOKLYN_ID,
+          name: 'Atlantic Ave @ Flatbush Ave',
+          latitude: 40.65,
+          longitude: -73.96,
+          area: 'Brooklyn',
+        }),
+      ]);
+    }
+    return Response.json([]);
+  });
+  const sources = await createCctvCatalog({ sourceRoot: '/nonexistent' })();
+  return { requested, sources };
+};
+
+/** Run one catalog refresh with CCTV_NYC_ENABLED set to `flag` (undefined
+ * leaves it unset), restoring the environment afterwards. */
+const runCatalogWithNycFlag = async (t, flag) => {
+  const saved = { ...process.env };
+  try {
+    delete process.env.CCTV_SOURCES_FILE;
+    delete process.env.CCTV_SOURCES_JSON;
+    if (flag === undefined) delete process.env.CCTV_NYC_ENABLED;
+    else process.env.CCTV_NYC_ENABLED = flag;
+    return await runCatalogWithMockedUpstreams(t);
+  } finally {
+    for (const key of Object.keys(process.env)) {
+      if (!(key in saved)) delete process.env[key];
+    }
+    Object.assign(process.env, saved);
+  }
+};
+
+test('CCTV_NYC_ENABLED=1 wires the NYC lane into the catalog', async (t) => {
+  const { requested, sources } = await runCatalogWithNycFlag(t, '1');
+  assert.ok(
+    requested.includes(NYC_CAMERAS_URL),
+    'the catalog refresh invokes the NYC loader',
+  );
+  assert.deepEqual(
+    sources.filter((s) => s.cityId === 'nyc').map((s) => s.id),
+    [`nyc-${MIDTOWN_ID}`, `nyc-${BROOKLYN_ID}`],
+    'NYC cameras reach the served catalog through the registered lane',
+  );
+});
+
+// NYC DOT requires a data-sharing agreement for this feed, so an install that
+// has not opted in must never contact it.
+for (const [label, flag] of [
+  ['an unset CCTV_NYC_ENABLED', undefined],
+  ['an empty CCTV_NYC_ENABLED', ''],
+  ['CCTV_NYC_ENABLED=0', '0'],
+  ['CCTV_NYC_ENABLED=true', 'true'],
+]) {
+  test(`${label} makes no NYC request`, async (t) => {
+    const { requested, sources } = await runCatalogWithNycFlag(t, flag);
+    assert.ok(requested.length > 0, 'the other packs still refreshed');
+    assert.equal(
+      requested.some((href) => href.includes('nyctmc.org')),
+      false,
+      'the lane never reaches its upstream',
+    );
+    assert.deepEqual(
+      sources.filter((s) => s.cityId === 'nyc'),
+      [],
+    );
+  });
+}
+
+test('the shipped catalog ceiling is not raised to make room for this pack', () => {
+  assert.equal(DEFAULT_CCTV_MAX_SOURCES, 4000);
+  assert.equal(DEFAULT_NYC_MAX_SOURCES, 250);
+});
+
+test('isLikelyNycCoordinate spans the five boroughs and rejects the rest', () => {
+  assert.equal(isLikelyNycCoordinate(40.758, -73.9855), true); // Times Square
+  assert.equal(isLikelyNycCoordinate(40.5795, -74.1502), true); // Staten Island
+  assert.equal(isLikelyNycCoordinate(40.8448, -73.8648), true); // Bronx
+  assert.equal(isLikelyNycCoordinate(40.5077, -74.2304), true); // southern SI slack
+  assert.equal(isLikelyNycCoordinate(30.2672, -97.7431), false); // Austin
+  assert.equal(isLikelyNycCoordinate(0, 0), false);
+  assert.equal(isLikelyNycCoordinate(NaN, -73.98), false);
+});

src/data/dataCredits.js

@@ -91,6 +91,13 @@ export function hideOsmCredit(viewer, owner) {
   return true;
 }
 
+/** NYC DOT asks every application that uses its data to carry this
+ * disclaimer verbatim (nyc.gov/html/dot/html/about/datafeeds.shtml). */
+export const NYC_DOT_DISCLAIMER =
+  'This application may contain and/or utilize information which was originally compiled by the New York City Department of Transportation (NYC DOT) for governmental purposes; the information may subsequently been modified by entity/entities other than NYC DOT. ' +
+  'NYC DOT and the City of New York make no representation as to the accuracy or usefulness of the information provided by this application or the information's suitability for any purpose and disclaim any liability for omissions or errors that may be contained therein. ' +
+  'The public is advised to observe posted signage for compliance with applicable laws and regulations.';
+
 export const DATA_CREDITS = [
   // ── Live sources ────────────────────────────────────────────────
   {
@@ -247,6 +254,13 @@ export const DATA_CREDITS = [
       '<a href="https://data.norge.no/nlod/en/2.0" target="_blank" rel="noopener">Norwegian licence for Open Government data (NLOD)</a> ' +
       'distributed by Statens vegvesen',
   },
+  {
+    key: 'nyc-cctv',
+    html:
+      'CCTV cameras &amp; frames (New York City, when enabled): ' +
+      '<a href="https://webcams.nyctmc.org/" target="_blank" rel="noopener">NYC DOT Traffic Management Center</a>. ' +
+      NYC_DOT_DISCLAIMER,
+  },
   {
     key: 'gbfs',
     html: 'Bikeshare availability: GBFS operator feeds (e.g. Austin BCycle)',

src/data/dataCredits.test.mjs

@@ -1,6 +1,6 @@
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
-import { DATA_CREDITS } from './dataCredits.js';
+import { DATA_CREDITS, NYC_DOT_DISCLAIMER } from './dataCredits.js';
 
 test('every credit carries a unique key and some markup to render', () => {
   const keys = DATA_CREDITS.map((entry) => entry.key);
@@ -120,3 +120,11 @@ test('tile attribution follows source changes and viewers have independent owner
   assert.equal(a.credits.size, 0);
   assert.equal(b.credits.size, 1);
 });
+
+test('the NYC camera credit carries NYC DOT’s requested disclaimer', () => {
+  const credit = DATA_CREDITS.find((entry) => entry.key === 'nyc-cctv');
+  assert.ok(credit, 'NYC DOT camera frames must be credited');
+  assert.ok(credit.html.includes(NYC_DOT_DISCLAIMER));
+  assert.match(credit.html, /make no representation as to the accuracy/);
+  assert.match(credit.html, /observe posted signage/);
+});

src/layers/streetLevel/index.js

@@ -108,7 +108,15 @@ export function createStreetLevelLayer({
       getSurface: () => state.surface,
       notify,
       actions: {
-        openImage: (imageId) => openImage(entry.def.id, imageId),
+        /** `{frame: false}` opens it without moving the camera. */
+        openImage: (imageId, options) =>
+          openImage(entry.def.id, imageId, options),
+        /** This provider's image nearest a point the user picked on the map. */
+        openNearest: (point) =>
+          layer.openNearest(point, {
+            providerIds: [entry.def.id],
+            frame: false,
+          }),
         /**
          * Show a provider error, or withdraw it (null). A withdrawal clears
          * only this provider's own error, never a newer one from elsewhere.
@@ -334,15 +342,36 @@ export function createStreetLevelLayer({
   function setProviderEnabled(providerId, on) {
     const entry = state.providers.get(providerId);
     if (!entry) return false;
+    const before = litIds();
     const next = on !== false;
     if (next)
       for (const other of state.providers.values())
         if (other !== entry && other.on) switchProvider(other, false);
     switchProvider(entry, next);
+    sourceChanged(before);
     notify();
     return true;
   }
 
+  const litIds = () =>
+    [...state.providers]
+      .filter(([, entry]) => entry.on)
+      .map(([id]) => id)
+      .join();
+
+  /**
+   * After a chip, voice or a link changed the lit source: a lookup still
+   * running and its spinner or error were about the source switched away
+   * (an open photo keeps its own state).
+   */
+  function sourceChanged(before) {
+    if (litIds() === before) return;
+    abortNearest();
+    if (state.street.open) return;
+    state.street.error = null;
+    state.street.loading = false;
+  }
+
   function switchProvider(entry, on) {
     if (entry.on === on) return;
     entry.on = on;
@@ -407,6 +436,9 @@ export function createStreetLevelLayer({
         hint: hintFor(entry, stats),
         error: stats.error || null,
         color: entry.def.colors.coverage,
+        coverageLabel: entry.def.coverageLabel || null,
+        highlightsSequence: entry.def.highlightsSequence !== false,
+        sinceBasis: entry.def.sinceBasis === 'upload' ? 'upload' : 'capture',
         groundClick: entry.def.groundClick === true,
         filters: [...filtersOf(entry.def)],
       };
@@ -606,9 +638,11 @@ export function createStreetLevelLayer({
         filter: state.filter,
       });
       const lit = litByParams(decoded.providers);
+      const before = litIds();
       for (const [id, entry] of state.providers)
         if (id !== lit) switchProvider(entry, false);
       if (lit) switchProvider(state.providers.get(lit), true);
+      sourceChanged(before);
       notify();
       setCoverageFilter(decoded.filter);
       return true;

src/layers/streetLevel/index.test.mjs

@@ -4,6 +4,7 @@ import * as Cesium from 'cesium';
 import { createStreetLevelLayer } from './index.js';
 import { MAPILLARY_CREDIT_HTML } from './providers/mapillary/policy.js';
 import { createMapillaryProvider } from './providers/mapillary/index.js';
+import { createKartaViewProvider } from './providers/kartaview/index.js';
 import { fakeStreetLevelProvider as fakeProvider } from '../../testSupport/streetLevelFakes.mjs';
 
 /**
@@ -92,8 +93,8 @@ function deferred() {
 }
 
 /** A provider whose viewer reports a pose for every image it opens. */
-function posingProvider() {
-  const provider = fakeProvider();
+function posingProvider(options) {
+  const provider = fakeProvider(options);
   const create = provider.create;
   provider.create = (context) => {
     const instance = create(context);
@@ -818,3 +819,127 @@ test('an empty provider composition enables and tears down without acquiring ima
   layer.enable(viewer);
   assert.deepEqual(layer.getUIState().providers, []);
 });
+
+test('a failed lookup’s error goes when another source is lit; a provider can open an image without framing', async (t) => {
+  const failing = fakeProvider({
+    nearestImage: async () => {
+      throw new Error('KartaView did not answer in time — try again');
+    },
+  });
+  const other = fakeProvider({ id: 'other', pickPrefix: 'oth:' });
+  const { layer, viewer } = await enabledLayer(t, [failing, other]);
+  layer.attachViewerHost({});
+  await layer.openNearest({ lat: 1, lon: 1 });
+  assert.match(layer.getUIState().street.error, /did not answer/);
+  layer.setProviderEnabled('other', true);
+  await settle();
+  assert.equal(layer.getUIState().street.error, null);
+  // A provider's own open (KartaView's ‹ ›) can leave the camera alone.
+  await other.context().actions.openImage('img-1', { frame: false });
+  assert.deepEqual(other.calls.open, ['img-1']);
+  assert.equal(viewer.flights.started, 0);
+});
+
+test('a provider’s own open can leave the camera where it is; a default open frames', async (t) => {
+  const provider = posingProvider();
+  const { layer, viewer } = await enabledLayer(t, [provider]);
+  layer.attachViewerHost({});
+  await provider.context().actions.openImage('img-1', { frame: false });
+  assert.deepEqual(provider.calls.open, ['img-1']);
+  assert.equal(viewer.flights.started, 0, 'frame: false keeps the camera');
+  await provider.context().actions.openImage('img-2');
+  assert.equal(viewer.flights.started, 1, 'a default open frames the image');
+});
+
+test('a provider’s openNearest (a line click) asks only that provider and leaves the camera', async (t) => {
+  const lit = posingProvider({ nearestImage: async () => 'lit-near' });
+  const other = fakeProvider({
+    id: 'other',
+    pickPrefix: 'oth:',
+    nearestImage: async () => 'other-near',
+  });
+  const { layer, viewer } = await enabledLayer(t, [lit, other]);
+  layer.attachViewerHost({});
+  const point = { lat: 38.58, lon: -121.49 };
+  // The other source is off: its click asks nobody else.
+  await other.context().actions.openNearest(point);
+  await settle();
+  assert.deepEqual(lit.calls.open, [], 'the lit source was not asked');
+  assert.deepEqual(other.calls.open, []);
+  await lit.context().actions.openNearest(point);
+  assert.deepEqual(lit.calls.open, ['lit-near']);
+  assert.equal(viewer.flights.started, 0, 'the user picked the spot');
+});
+
+test('KartaView through the core: its own swatch without Selected, its lines counted as streets', async (t) => {
+  const kartaView = createKartaViewProvider({
+    source: {
+      getTile: async () => ({ lines: [] }),
+      nearestPhotos: async () => [],
+      getPhoto: async () => {
+        throw new Error('KartaView has no such photo');
+      },
+      getSequencePhotos: async () => ({ photos: [], hasMore: false }),
+      probeImage: async () => true,
+    },
+  });
+  const { layer } = await enabledLayer(t, [kartaView]);
+  layer.setProviderEnabled('kartaview', true);
+  await settle();
+  const ui = layer.getUIState();
+  assert.deepEqual(
+    ui.legend.map((entry) => entry.key),
+    ['kartaview'],
+  );
+  assert.equal(ui.coverage.label?.noun, 'streets');
+  assert.equal(
+    ui.providers.find((p) => p.id === 'kartaview').highlightsSequence,
+    false,
+  );
+});
+
+test('switching source by params (the chip path) stops a running lookup and clears its spinner and error', async (t) => {
+  const slow = slowLookups();
+  const looking = fakeProvider({ nearestImage: slow.nearestImage });
+  const other = fakeProvider({ id: 'other', pickPrefix: 'oth:' });
+  const { layer } = await enabledLayer(t, [looking, other]);
+  layer.attachViewerHost({});
+  const opening = layer.openNearest({ lat: 1, lon: 1 });
+  await settle();
+  assert.equal(layer.getUIState().street.loading, true);
+  layer.setParams({ mapillary: false, other: true });
+  assert.equal(slow.lookups[0].signal.aborted, true, 'the lookup is stopped');
+  assert.equal(
+    layer.getUIState().street.loading,
+    false,
+    'no spinner left behind',
+  );
+  // The stopped lookup answers late: nothing opens, nothing is reported.
+  slow.lookups[0].answer.resolve('img1');
+  assert.equal(await opening, false);
+  assert.deepEqual(looking.calls.open, []);
+  assert.equal(layer.getUIState().street.error, null);
+});
+
+test('switching source by params clears a failed lookup’s error; reapplying the same switches does not', async (t) => {
+  const failing = fakeProvider({
+    nearestImage: async () => {
+      throw new Error('KartaView did not answer in time — try again');
+    },
+  });
+  const { layer: second } = await enabledLayer(t, [
+    failing,
+    fakeProvider({ id: 'other', pickPrefix: 'oth:' }),
+  ]);
+  second.attachViewerHost({});
+  await second.openNearest({ lat: 1, lon: 1 });
+  assert.match(second.getUIState().street.error, /did not answer/);
+  second.setParams({ mapillary: false, other: true });
+  assert.equal(second.getUIState().street.error, null);
+  // Reapplying the same switches (a restore) leaves state alone.
+  await second.openNearest({ lat: 1, lon: 1 });
+  const kept = second.getUIState().street.error;
+  assert.match(kept, /No street-level imagery/);
+  second.setParams({ mapillary: false, other: true });
+  assert.equal(second.getUIState().street.error, kept);
+});

src/layers/streetLevel/lineCoverage.js

@@ -0,0 +1,936 @@
+import * as Cesium from 'cesium';
+import { passesImageryFilter } from './filter.js';
+import {
+  createHorizonCull,
+  groundUnderCamera,
+  metresBetween,
+  viewFocus,
+  visibleBbox,
+  whenIdle,
+} from './view.js';
+import { densifyLine, MESH_DENSIFY_DEG } from './groundCast.js';
+import { MESH_SAMPLE_RADIUS_M } from './meshSampler.js';
+import { tileBounds, tilesForBbox } from './tileMath.js';
+
+/** Draped lines stay at most this long while a tile's cast lines build. */
+export const SWAP_MAX_WAIT_MS = 4000;
+/** Tiles touched by new mesh samples are redrawn at most this often. */
+const REMESH_INTERVAL_MS = 1500;
+/** Gap between redrawing one dirty tile and the next. */
+const REMESH_STAGGER_MS = 120;
+/** Old-zoom tiles are kept at most this long after a zoom change. */
+const STALE_TILE_MAX_MS = 6000;
+/** Sequences per primitive: smaller batches build, and show, sooner. */
+const SEQUENCE_PRIMITIVE_BATCH = 120;
+
+/** Separates a multi-part sequence's part index from its id in pick ids. */
+const PART_SEPARATOR = '~';
+
+/** Pick ids for every part of a sequence; the first part is unsuffixed. */
+function partIds(sequence, prefix) {
+  return sequence.parts.map((_, index) =>
+    index
+      ? `${prefix}${sequence.id}${PART_SEPARATOR}${index}`
+      : `${prefix}${sequence.id}`,
+  );
+}
+
+/** Sequence id for any part's pick id (`<prefix><id>[~<part>]`), else null. */
+export function sequenceIdFromPick(pickId, prefix) {
+  if (typeof pickId !== 'string' || !prefix || !pickId.startsWith(prefix))
+    return null;
+  const rest = pickId.slice(prefix.length);
+  const cut = rest.indexOf(PART_SEPARATOR);
+  return cut === -1 ? rest : rest.slice(0, cut);
+}
+
+/**
+ * Whether any point of `box` ({west, south, east, north}) is within the mesh
+ * sampler's range of `centre`, the ground point under the camera.
+ */
+export function meshBoxInRange(box, centre) {
+  // Move the camera's longitude to the box's side of the date line first:
+  // clamping 179.999 into a box at -179.99 would pick its far edge.
+  const lon =
+    centre.lon +
+    360 * Math.round(((box.west + box.east) / 2 - centre.lon) / 360);
+  const nearest = {
+    lon: Math.min(box.east, Math.max(box.west, lon)),
+    lat: Math.min(box.north, Math.max(box.south, centre.lat)),
+  };
+  return metresBetween(centre, nearest) <= MESH_SAMPLE_RADIUS_M;
+}
+
+/**
+ * @typedef {object} LineCoverageTuning
+ * @property {number} maxTiles            Line tiles drawn at once.
+ * @property {number} overviewMaxTiles    Overview tiles drawn at once.
+ * @property {number} maxSequences        Lines drawn at once, over every tile.
+ * @property {number} lineWidthPx
+ * @property {number} overviewPointPx
+ * @property {number} moveDebounceMs      Camera rest before the tile set is recomputed.
+ * @property {number} viewRangeMinM       Street-zoom coverage reaches at least this far…
+ * @property {number} viewRangePerHeight  …or camera height times this.
+ * @property {number} viewNearM           Ground always covered around a tilted camera.
+ */
+
+/**
+ * Camera-driven coverage from any XYZ line-tile source: overview points from
+ * orbit, sequence lines near the ground. In terrain surface mode a tile is
+ * drawn draped first, then swapped for lines cast to the bare earth (draped
+ * lines would land on roofs), so coverage never waits on terrain heights.
+ *
+ * @param {object} options
+ * @param {object} options.state  Provider state: `context`, `services`, `viewer`, `coverage`, `sequence`, key flags.
+ * @param {(tile: {x: number, y: number, z: number}, init: {signal: AbortSignal}) => Promise<{sequences: Array<object>, overview: Array<object>}>} options.fetchTile
+ *   A decoded tile. Sequences are `{id, parts, capturedAt, isPano}`; overview
+ *   points `{lon, lat, capturedAt, isPano}`. A rejection may carry
+ *   `keyRequired`, `keyRejected` or `retryAfterSec`.
+ * @param {(heightM: number|null) => {zoom: number, kind: 'sequence'|'overview'}|null} options.zoomFor
+ *   Tile zoom for a camera height above ground; null draws nothing.
+ * @param {{coverage: string, selected: string}} options.colors
+ * @param {string} options.pickPrefix   Pick-id prefix of the lines.
+ * @param {string} options.renderKey    Render-governor reason.
+ * @param {LineCoverageTuning} options.tuning
+ * @param {{keyRejected?: string, rateLimited: string, tooHigh?: string}} options.messages
+ * @param {(sequence: object, filter: object) => boolean} [options.passes]  Whether the imagery filter keeps a line or point.
+ */
+export function createLineCoverage({
+  state,
+  fetchTile,
+  zoomFor,
+  colors,
+  pickPrefix,
+  renderKey,
+  tuning,
+  messages,
+  passes = passesImageryFilter,
+}) {
+  const { render } = state.services;
+  const perTileSequenceCap = Math.floor(tuning.maxSequences / tuning.maxTiles);
+
+  /** Colour for a line: the provider's, GEV cyan while selected. */
+  function sequenceColor({ selected = false } = {}) {
+    return selected
+      ? Cesium.Color.fromCssColorString(colors.selected)
+      : Cesium.Color.fromCssColorString(colors.coverage).withAlpha(0.92);
+  }
+
+  function requestRender() {
+    render?.governorRequestRender?.(renderKey);
+  }
+
+  function ensureTerrainReady() {
+    return (state.coverage.terrainReady ||=
+      Cesium.GroundPolylinePrimitive.initializeTerrainHeights());
+  }
+
+  function tileKey({ x, y, z }) {
+    return `${z}/${x}/${y}`;
+  }
+
+  /** The imagery filter, resolved now: "since N days" moves with the clock. */
+  function filter() {
+    return state.context.getFilter();
+  }
+
+  function terrainMode() {
+    return (
+      state.context.getSurface?.() === 'terrain' &&
+      Boolean(state.context.groundCaster)
+    );
+  }
+
+  /**
+   * A tile's sequences, filtered then capped: capping first could leave a
+   * dense tile of newer flat captures with no 360° lines at all.
+   */
+  function drawnSequences(entry) {
+    const drawn = [];
+    const current = filter();
+    for (const sequence of entry.sequenceList) {
+      if (drawn.length >= perTileSequenceCap) break;
+      if (passes(sequence, current)) drawn.push(sequence);
+    }
+    return drawn;
+  }
+
+  /**
+   * Batched primitives for a tile's sequence parts: cast polylines where
+   * terrain heights are cached, draped ground lines otherwise. Each batch
+   * records the selection its colours were built with.
+   */
+  function buildSequencePrimitives(sequences) {
+    const ground = terrainMode() ? state.context.groundCaster : null;
+    const meshAt = ground ? state.context.meshSampler?.meshAt : undefined;
+    const selectedId = state.sequence.selectedId ?? null;
+    const draped = [];
+    const cast = [];
+    for (const sequence of sequences) {
+      const color = Cesium.ColorGeometryInstanceAttribute.fromColor(
+        sequenceColor({ selected: sequence.id === selectedId }),
+      );
+      const ids = partIds(sequence, pickPrefix);
+      sequence.parts.forEach((coordinates, index) => {
+        const flat = ground?.castLine(coordinates, { meshAt });
+        let positions;
+        try {
+          positions = flat
+            ? Cesium.Cartesian3.fromDegreesArrayHeights(flat)
+            : Cesium.Cartesian3.fromDegreesArray(coordinates.flat());
+        } catch {
+          return;
+        }
+        if (positions.length < 2) return;
+        const geometry = flat
+          ? new Cesium.PolylineGeometry({
+              positions,
+              width: tuning.lineWidthPx,
+              vertexFormat: Cesium.PolylineColorAppearance.VERTEX_FORMAT,
+              arcType: Cesium.ArcType.NONE,
+            })
+          : new Cesium.GroundPolylineGeometry({
+              positions,
+              width: tuning.lineWidthPx,
+            });
+        (flat ? cast : draped).push(
+          new Cesium.GeometryInstance({
+            geometry,
+            id: ids[index],
+            attributes: { color },
+          }),
+        );
+      });
+    }
+    const primitives = [];
+    for (let i = 0; i < draped.length; i += SEQUENCE_PRIMITIVE_BATCH)
+      primitives.push({
+        onGround: true,
+        selectedId,
+        primitive: new Cesium.GroundPolylinePrimitive({
+          geometryInstances: draped.slice(i, i + SEQUENCE_PRIMITIVE_BATCH),
+          appearance: new Cesium.PolylineColorAppearance(),
+          classificationType: Cesium.ClassificationType.BOTH,
+          asynchronous: true,
+          allowPicking: true,
+        }),
+      });
+    for (let i = 0; i < cast.length; i += SEQUENCE_PRIMITIVE_BATCH)
+      primitives.push({
+        onGround: false,
+        selectedId,
+        primitive: new Cesium.Primitive({
+          geometryInstances: cast.slice(i, i + SEQUENCE_PRIMITIVE_BATCH),
+          appearance: new Cesium.PolylineColorAppearance({ translucent: true }),
+          asynchronous: true,
+          allowPicking: true,
+        }),
+      });
+    return { primitives, draped, cast: cast.length };
+  }
+
+  /**
+   * Fetch the terrain heights a tile's lines need, then redraw it cast.
+   * `castRequested` stops the redraw from casting again at once; a refresh
+   * `retry`s a tile whose lines are still draped (a failed or partial cast),
+   * and it is redrawn only when more of its lines can be cast.
+   */
+  function castTile(entry, { retry = false } = {}) {
+    if ((entry.castRequested && !retry) || entry.castAbort || !terrainMode())
+      return;
+    entry.castRequested = true;
+    entry.castAbort = new AbortController();
+    const { signal } = entry.castAbort;
+    const lines = [...entry.sequences.values()].flatMap(
+      (sequence) => sequence.parts,
+    );
+    const caster = state.context.groundCaster;
+    caster.prepareLines(lines, { signal }).then(() => {
+      if (entry.castAbort?.signal === signal) entry.castAbort = null;
+      const attached = [...state.coverage.tiles.values()].includes(entry);
+      if (signal.aborted || !attached || !terrainMode()) return;
+      // Nothing new to cast: keep what is drawn until the next refresh.
+      // Counted like buildSequencePrimitives: a cast line needs two points.
+      const castable = lines.filter(
+        (coords) => caster.castLine(coords)?.length >= 6,
+      ).length;
+      if (castable <= (entry.castLines || 0)) {
+        entry.castRequested = (entry.castLines || 0) > 0;
+        return;
+      }
+      // A remesh may have cleared the flag while this was in flight.
+      entry.castRequested = true;
+      redrawTile(entry);
+      requestMesh(entry);
+    });
+  }
+
+  /** Rebuild a tile's lines; the old ones stay up until the new are ready. */
+  function redrawTile(entry) {
+    const previous = entry.primitives;
+    entry.primitives = [];
+    attachPrimitive(entry);
+    removeWhenReady(entry, previous);
+  }
+
+  /** Lon/lat under the camera, where mesh range is measured from. */
+  function meshCentre() {
+    const carto = state.viewer?.camera?.positionCartographic;
+    if (!carto) return null;
+    return {
+      lon: Cesium.Math.toDegrees(carto.longitude),
+      lat: Cesium.Math.toDegrees(carto.latitude),
+    };
+  }
+
+  /**
+   * A tile's drawn lines with bounding boxes, built once per filter; mesh
+   * points are densified the first time a line is in range.
+   */
+  function meshParts(entry) {
+    if (entry.meshParts) return entry.meshParts;
+    entry.meshParts = [];
+    for (const sequence of entry.sequences.values())
+      for (const part of sequence.parts) {
+        const box = {
+          west: Infinity,
+          south: Infinity,
+          east: -Infinity,
+          north: -Infinity,
+        };
+        for (const [lon, lat] of part) {
+          if (lon < box.west) box.west = lon;
+          if (lon > box.east) box.east = lon;
+          if (lat < box.south) box.south = lat;
+          if (lat > box.north) box.north = lat;
+        }
+        entry.meshParts.push({ part, box, points: null });
+      }
+    return entry.meshParts;
+  }
+
+  /**
+   * Ask for mesh samples under a cast tile's lines within the sampler's range
+   * of the camera; the rest are asked for when a camera move brings them in.
+   */
+  function requestMesh(entry) {
+    const sampler = state.context.meshSampler;
+    if (!sampler || entry.kind !== 'sequence' || !terrainMode()) return;
+    const centre = meshCentre();
+    if (!centre || !entry.bounds || !meshBoxInRange(entry.bounds, centre))
+      return;
+    const points = [];
+    for (const line of meshParts(entry)) {
+      if (!meshBoxInRange(line.box, centre)) continue;
+      line.points ||= densifyLine(line.part, MESH_DENSIFY_DEG);
+      for (const point of line.points) points.push(point);
+    }
+    if (points.length) sampler.request(points);
+  }
+
+  /** Redraw the tiles new mesh samples fall in, throttled. */
+  function onMeshSampled(batch) {
+    if (!terrainMode() || !state.context.isActive()) return;
+    for (const entry of state.coverage.tiles.values()) {
+      if (entry.kind !== 'sequence' || !entry.bounds) continue;
+      const { west, south, east, north } = entry.bounds;
+      if (
+        batch.some(
+          ([lon, lat]) =>
+            lon >= west && lon <= east && lat >= south && lat <= north,
+        )
+      )
+        state.coverage.remeshDirty.add(entry);
+    }
+    if (!state.coverage.remeshDirty.size || state.coverage.remeshTimer) return;
+    const wait = Math.max(
+      0,
+      REMESH_INTERVAL_MS - (Date.now() - (state.coverage.remeshAt || 0)),
+    );
+    state.coverage.remeshTimer = setTimeout(remesh, wait);
+  }
+
+  /** Redraw one dirty tile per idle slice, so a burst of samples never stalls a frame. */
+  function remesh() {
+    state.coverage.remeshTimer = null;
+    state.coverage.remeshAt = Date.now();
+    if (!terrainMode() || !state.context.isActive()) {
+      state.coverage.remeshDirty.clear();
+      return;
+    }
+    const attached = new Set(state.coverage.tiles.values());
+    const [entry] = state.coverage.remeshDirty;
+    if (!entry) return;
+    state.coverage.remeshDirty.delete(entry);
+    if (attached.has(entry)) {
+      redrawTile(entry);
+      requestRender();
+    }
+    if (state.coverage.remeshDirty.size)
+      state.coverage.remeshTimer = setTimeout(
+        () => whenIdle(remesh, 500),
+        REMESH_STAGGER_MS,
+      );
+  }
+
+  state.coverage.remeshDirty = new Set();
+  state.context.meshSampler?.onSampled(onMeshSampled);
+
+  /**
+   * Remove a tile's previous primitives once all its current ones are ready
+   * (or after a few seconds); detaching the tile removes them at once.
+   */
+  function removeWhenReady(entry, old) {
+    const scene = state.viewer?.scene;
+    finishSwap(entry);
+    if (!scene?.postRender) {
+      removePrimitives(old);
+      return;
+    }
+    const fresh = entry.primitives;
+    const started = Date.now();
+    const stop = scene.postRender.addEventListener(() => {
+      const ready = fresh.every(
+        ({ primitive }) => primitive.ready || primitive.isDestroyed?.(),
+      );
+      if (!ready && Date.now() - started < SWAP_MAX_WAIT_MS) {
+        requestRender();
+        return;
+      }
+      finishSwap(entry);
+      requestRender();
+    });
+    entry.swap = { old, stop };
+    requestRender();
+  }
+
+  function finishSwap(entry) {
+    if (!entry.swap) return;
+    entry.swap.stop();
+    removePrimitives(entry.swap.old);
+    entry.swap = null;
+  }
+
+  function buildOverviewCollection(points) {
+    const collection = new Cesium.PointPrimitiveCollection({
+      blendOption: Cesium.BlendOption.TRANSLUCENT,
+    });
+    const tint = Cesium.Color.fromCssColorString(colors.coverage).withAlpha(
+      0.85,
+    );
+    const drawn = [];
+    const current = filter();
+    for (const point of points) {
+      if (!passes(point, current)) continue;
+      drawn.push(
+        collection.add({
+          position: Cesium.Cartesian3.fromDegrees(point.lon, point.lat),
+          color: tint,
+          pixelSize: tuning.overviewPointPx,
+          // Google 3D terrain and clouds must not hide the near side's dots;
+          // the horizon cull hides the far side's, which this lets through.
+          disableDepthTestDistance: Number.POSITIVE_INFINITY,
+        }),
+      );
+    }
+    return { collection, points: drawn };
+  }
+
+  /** Every overview point on the globe, current zoom and old alike. */
+  function* overviewPoints() {
+    for (const entry of drawnEntries())
+      if (entry.overviewPoints) yield* entry.overviewPoints;
+  }
+
+  // Overview points skip the depth test: hide the far hemisphere's.
+  const horizon = createHorizonCull({
+    getViewer: () => state.viewer,
+    items: overviewPoints,
+    onChange: requestRender,
+  });
+
+  function attachPrimitive(entry) {
+    const scene = state.viewer?.scene;
+    if (!scene) return;
+    if (entry.kind === 'sequence') {
+      // Lookup, picking and counts follow what is drawn, not the whole tile.
+      const sequences = drawnSequences(entry);
+      entry.sequences = new Map(sequences.map((s) => [s.id, s]));
+      const { primitives, draped, cast } = buildSequencePrimitives(sequences);
+      entry.primitives = primitives;
+      entry.count = sequences.length;
+      for (const { primitive, onGround } of primitives)
+        (onGround ? scene.groundPrimitives : scene.primitives).add(primitive);
+      // Fewer lines cast than last time: the caster has dropped heights this
+      // tile used (a full cache), so it must be cast again.
+      if (cast < (entry.castLines || 0)) entry.castRequested = false;
+      entry.castLines = cast;
+      entry.drapedLines = draped.length;
+      if (draped.length) castTile(entry);
+      watchSelection();
+    } else {
+      const { collection, points } = buildOverviewCollection(entry.points);
+      entry.primitive = collection;
+      entry.overviewPoints = points;
+      entry.count = points.length;
+      scene.primitives.add(collection);
+      // Cull the new points now, then all of them whenever the camera moves.
+      horizon.update(points);
+    }
+  }
+
+  function removePrimitives(list) {
+    const scene = state.viewer?.scene;
+    for (const { primitive, onGround } of list || []) {
+      try {
+        (onGround ? scene?.groundPrimitives : scene?.primitives)?.remove(
+          primitive,
+        );
+      } catch {
+        /* already gone */
+      }
+    }
+  }
+
+  function detachPrimitive(entry) {
+    const scene = state.viewer?.scene;
+    finishSwap(entry);
+    removePrimitives(entry.primitives);
+    entry.primitives = [];
+    if (entry.primitive) {
+      try {
+        scene?.primitives?.remove(entry.primitive);
+      } catch {
+        /* already gone */
+      }
+      entry.primitive = null;
+      entry.overviewPoints = null;
+    }
+  }
+
+  /** Stop a tile's pending terrain lookup (tile dropped or retired). */
+  function cancelCast(entry) {
+    entry.castAbort?.abort();
+    entry.castAbort = null;
+  }
+
+  function removeTile(key) {
+    const entry = state.coverage.tiles.get(key);
+    if (!entry) return;
+    cancelCast(entry);
+    detachPrimitive(entry);
+    state.coverage.tiles.delete(key);
+  }
+
+  async function loadTile(tile, kind) {
+    const key = tileKey(tile);
+    if (state.coverage.tiles.has(key) || state.coverage.pending.has(key))
+      return;
+    const controller = new AbortController();
+    state.coverage.pending.set(key, controller);
+    notify();
+    try {
+      // Fetch and the one-time terrain-height table load run side by side,
+      // both handled from the start so an early tile failure is not unhandled.
+      const [decoded] = await Promise.all([
+        fetchTile(tile, { signal: controller.signal }),
+        kind === 'sequence' ? ensureTerrainReady() : null,
+      ]);
+      // Only an abort, a retire, a clear or a newer request for this tile
+      // discards the bytes; a refresh that still wants the tile keeps them.
+      const current = () =>
+        state.coverage.pending.get(key) === controller &&
+        !state.coverage.tiles.has(key);
+      if (
+        controller.signal.aborted ||
+        !current() ||
+        kind !== state.coverage.kind ||
+        tile.z !== state.coverage.zoom
+      )
+        return;
+      const entry = { kind, primitive: null, primitives: [], count: 0 };
+      // Padded: vector tiles carry a small buffer past their edge.
+      const bounds = tileBounds(tile.x, tile.y, tile.z);
+      const pad = (bounds.east - bounds.west) * 0.05;
+      entry.bounds = {
+        west: bounds.west - pad,
+        east: bounds.east + pad,
+        south: bounds.south - pad,
+        north: bounds.north + pad,
+      };
+      if (kind === 'sequence') {
+        // Newest first; the per-tile cap applies to what passes the filter.
+        entry.sequenceList = decoded.sequences.sort(
+          (a, b) => (b.capturedAt || 0) - (a.capturedAt || 0),
+        );
+        entry.sequences = new Map();
+        entry.total = decoded.sequences.length;
+      } else {
+        entry.points = decoded.overview;
+        entry.sequences = new Map();
+        entry.total = decoded.overview.length;
+      }
+      attachPrimitive(entry);
+      state.coverage.tiles.set(key, entry);
+      state.coverage.lastError = null;
+      requestRender();
+    } catch (error) {
+      if (
+        controller.signal.aborted ||
+        state.coverage.pending.get(key) !== controller
+      )
+        return;
+      state.coverage.lastError = error?.message || 'Coverage tile failed';
+      if (error?.keyRequired) state.keyRequired = true;
+      if (error?.keyRejected) {
+        // Every other tile would be refused too: stop asking.
+        state.keyRejected = true;
+        state.coverage.lastError =
+          messages.keyRejected || state.coverage.lastError;
+      }
+      if (error?.retryAfterSec) holdFor(error.retryAfterSec);
+    } finally {
+      // Only the request that still owns the key settles it: a superseded one
+      // must not drop a newer request's entry (which is what counts as loading).
+      if (state.coverage.pending.get(key) === controller) {
+        state.coverage.pending.delete(key);
+        if (!state.coverage.pending.size) purgeStale();
+      }
+      notify();
+    }
+  }
+
+  /**
+   * The source is rate-limiting: keep what is drawn, request nothing until the
+   * wait is over, then refresh once.
+   */
+  function holdFor(seconds) {
+    clearTimeout(state.coverage.holdTimer);
+    state.coverage.holdUntil = Date.now() + seconds * 1000;
+    state.coverage.lastError = messages.rateLimited;
+    state.coverage.holdTimer = setTimeout(() => {
+      state.coverage.holdTimer = null;
+      state.coverage.holdUntil = 0;
+      if (state.coverage.lastError === messages.rateLimited)
+        state.coverage.lastError = null;
+      refresh();
+    }, seconds * 1000);
+  }
+
+  /** Forget refusals when the provider goes off, so the next run asks again. */
+  function resetErrors() {
+    clearTimeout(state.coverage.holdTimer);
+    state.coverage.holdTimer = null;
+    state.coverage.holdUntil = 0;
+    state.coverage.lastError = null;
+    state.keyRejected = false;
+  }
+
+  /** Drop the previous zoom's tiles once the new ones are on screen. */
+  function purgeStale() {
+    clearTimeout(state.coverage.staleTimer);
+    state.coverage.staleTimer = null;
+    if (!state.coverage.stale.size) return;
+    for (const entry of state.coverage.stale.values()) detachPrimitive(entry);
+    state.coverage.stale.clear();
+    requestRender();
+  }
+
+  /** Move tiles to the stale set: the old zoom shows until the new one loads. */
+  function retire() {
+    for (const controller of state.coverage.pending.values())
+      controller.abort();
+    state.coverage.pending.clear();
+    for (const [key, entry] of state.coverage.tiles) {
+      cancelCast(entry);
+      const previous = state.coverage.stale.get(key);
+      if (previous) detachPrimitive(previous);
+      state.coverage.stale.set(key, entry);
+    }
+    state.coverage.tiles.clear();
+    clearTimeout(state.coverage.staleTimer);
+    state.coverage.staleTimer = setTimeout(purgeStale, STALE_TILE_MAX_MS);
+  }
+
+  function notify() {
+    state.context.notify();
+  }
+
+  /**
+   * Whether the screen centre meets the ground further ahead than the camera
+   * is high (a view tilted above 45°), or misses it.
+   */
+  function isTilted({ nadir, ahead }, height) {
+    if (!ahead) return true;
+    return metresBetween(nadir, ahead) > Math.max(1, height);
+  }
+
+  /** Recompute the tile set for the current camera and reconcile primitives. */
+  function refresh() {
+    const viewer = state.viewer;
+    if (!viewer || !state.context.isActive() || state.keyRequired) return;
+    if (state.statusKnown === false) return;
+    if (state.keyRejected || state.coverage.holdUntil > Date.now()) return;
+    const ground = groundUnderCamera(viewer, {
+      groundAt: state.context.groundCaster?.groundAt,
+    });
+    const cameraHeight = viewer.camera?.positionCartographic?.height;
+    const height = Number.isFinite(cameraHeight)
+      ? cameraHeight - (ground ?? 0)
+      : null;
+    const level = zoomFor(height);
+    const zoom = level?.zoom ?? null;
+    const kind = level?.kind ?? null;
+    // At street zooms the rays meet the ground where it really is (1,600 m up
+    // in Denver; Google 3D hides the globe) and stop short of the horizon.
+    const ranged =
+      kind === 'sequence'
+        ? {
+            groundHeight: ground,
+            maxRange: Math.max(
+              tuning.viewRangeMinM,
+              height * tuning.viewRangePerHeight,
+            ),
+          }
+        : {};
+    // Tilted street views rank tiles along the line of sight, from the ground
+    // under the camera to the ground at the centre of the screen.
+    const focus = kind === 'sequence' ? viewFocus(viewer, ranged) : null;
+    let bbox = visibleBbox(viewer, {
+      ...ranged,
+      // A tilted view's screen rows jump from the first metres to the horizon:
+      // keep the ground around the camera too. Looking down needs no help.
+      nearRange: focus && isTilted(focus, height) ? tuning.viewNearM : null,
+    });
+    if (kind === 'overview' && (!bbox || zoom <= 1))
+      bbox = [-180, -85, 180, 85];
+    if (zoom == null || !bbox) {
+      state.coverage.hint =
+        zoom == null && Number.isFinite(height) && messages.tooHigh
+          ? messages.tooHigh
+          : 'Point the camera at the globe for street-level coverage';
+      clear();
+      notify();
+      return;
+    }
+    state.coverage.hint = '';
+    if (zoom !== state.coverage.zoom || kind !== state.coverage.kind) {
+      retire();
+      state.coverage.zoom = zoom;
+      state.coverage.kind = kind;
+    }
+    const { tiles } = tilesForBbox(bbox, zoom, {
+      limit: kind === 'sequence' ? tuning.maxTiles : tuning.overviewMaxTiles,
+      focus: focus && { from: focus.nadir, to: focus.ahead },
+    });
+    const wanted = new Set(tiles.map(tileKey));
+    for (const key of [...state.coverage.tiles.keys()])
+      if (!wanted.has(key)) removeTile(key);
+    for (const [key, controller] of [...state.coverage.pending])
+      if (!wanted.has(key)) {
+        // The aborted request no longer owns its key, so its `finally` will
+        // not settle it: settle it here.
+        controller.abort();
+        state.coverage.pending.delete(key);
+      }
+    for (const tile of tiles) loadTile(tile, kind);
+    if (!state.coverage.pending.size) purgeStale();
+    // The camera moved: cells that were out of the sampler's range may not be,
+    // and lines left draped by a failed, partial or dropped cast get another try.
+    if (terrainMode())
+      for (const entry of state.coverage.tiles.values()) {
+        if (entry.castRequested) requestMesh(entry);
+        if (entry.drapedLines) castTile(entry, { retry: true });
+      }
+    notify();
+  }
+
+  function scheduleRefresh() {
+    clearTimeout(state.coverage.debounceTimer);
+    state.coverage.debounceTimer = setTimeout(refresh, tuning.moveDebounceMs);
+  }
+
+  function attach(viewer) {
+    detach();
+    const remove = viewer.camera.changed.addEventListener(scheduleRefresh);
+    const removeEnd = viewer.camera.moveEnd.addEventListener(scheduleRefresh);
+    state.coverage.removeCameraListener = () => {
+      remove();
+      removeEnd();
+    };
+    refresh();
+  }
+
+  function detach() {
+    clearTimeout(state.coverage.debounceTimer);
+    state.coverage.debounceTimer = null;
+    state.coverage.removeCameraListener?.();
+    state.coverage.removeCameraListener = null;
+  }
+
+  function clear() {
+    for (const controller of state.coverage.pending.values())
+      controller.abort();
+    state.coverage.pending.clear();
+    for (const key of [...state.coverage.tiles.keys()]) removeTile(key);
+    purgeStale();
+    state.coverage.zoom = null;
+    state.coverage.kind = null;
+    clearTimeout(state.coverage.remeshTimer);
+    state.coverage.remeshTimer = null;
+    state.coverage.remeshDirty.clear();
+    stopSelectionWatch();
+    horizon.stop();
+    requestRender();
+  }
+
+  /** Rebuild every loaded tile from its decoded cache (after a filter change). */
+  function rebuild() {
+    purgeStale();
+    for (const entry of state.coverage.tiles.values()) {
+      cancelCast(entry);
+      entry.castRequested = false;
+      entry.meshParts = null;
+      detachPrimitive(entry);
+      attachPrimitive(entry);
+    }
+    requestRender();
+    notify();
+  }
+
+  /**
+   * Load every tile again (a source that filters on its server had its
+   * filter changed); the lines drawn now show until the new ones are in.
+   */
+  function reload() {
+    retire();
+    refresh();
+  }
+
+  /**
+   * Redraw tiles draped or cast for the new surface mode, then re-pick the
+   * zoom, since the ground height under the camera may have changed.
+   */
+  function setSurface() {
+    if (!state.context.isActive()) return;
+    rebuild();
+    refresh();
+  }
+
+  /** Recolour every part of a sequence in one ready primitive. */
+  function recolorInstances(primitive, sequence, selected) {
+    const value = sequenceColor({ selected });
+    for (const instanceId of partIds(sequence, pickPrefix)) {
+      try {
+        const attributes = primitive.getGeometryInstanceAttributes(instanceId);
+        if (attributes)
+          attributes.color = Cesium.ColorGeometryInstanceAttribute.toValue(
+            value,
+            attributes.color,
+          );
+      } catch {
+        /* instance not in this primitive */
+      }
+    }
+  }
+
+  /** Every tile on the globe: the current zoom's and the stale zoom's. */
+  function drawnEntries() {
+    return [...state.coverage.tiles.values(), ...state.coverage.stale.values()];
+  }
+
+  /** A tile's primitives on the globe: its own, and the ones a swap still shows. */
+  function drawnRecords(entry) {
+    const records = entry.primitives || [];
+    return entry.swap ? [...records, ...entry.swap.old] : records;
+  }
+
+  /** Recolour one sequence, every part of it, in place (selection highlight). */
+  function recolorSequence(id, selected) {
+    for (const entry of drawnEntries()) {
+      const sequence = entry.sequences.get(id);
+      if (!sequence) continue;
+      for (const record of drawnRecords(entry)) {
+        // Still building: `syncSelection` catches it up once it is ready.
+        if (!record.primitive.ready) continue;
+        recolorInstances(record.primitive, sequence, selected);
+        if (selected) record.selectedId = id;
+        else if (record.selectedId === id) record.selectedId = null;
+      }
+    }
+    requestRender();
+  }
+
+  /**
+   * Bring a ready primitive's highlight up to the current selection, when
+   * it was built with another one (or none). True when it changed.
+   */
+  function syncSelection(entry, record) {
+    const current = state.sequence.selectedId ?? null;
+    if (record.selectedId === current || !record.primitive.ready) return false;
+    const previous =
+      record.selectedId && entry.sequences.get(record.selectedId);
+    if (previous) recolorInstances(record.primitive, previous, false);
+    const next = current && entry.sequences.get(current);
+    if (next) recolorInstances(record.primitive, next, true);
+    record.selectedId = current;
+    return true;
+  }
+
+  /**
+   * A primitive cannot be recoloured until it is ready, so while any is
+   * building, catch each one up with the selection as it becomes ready.
+   */
+  function watchSelection() {
+    const scene = state.viewer?.scene;
+    if (state.coverage.stopSelectionWatch || !scene?.postRender) return;
+    const stop = scene.postRender.addEventListener(() => {
+      let building = false;
+      let changed = false;
+      for (const entry of drawnEntries()) {
+        for (const record of entry.primitives || []) {
+          if (!record.primitive.ready) building = true;
+          else if (syncSelection(entry, record)) changed = true;
+        }
+        // Lines a swap still shows were ready (or never show): catch up only.
+        for (const record of entry.swap?.old || [])
+          if (syncSelection(entry, record)) changed = true;
+      }
+      if (changed) requestRender();
+      if (!building) stopSelectionWatch();
+    });
+    state.coverage.stopSelectionWatch = stop;
+  }
+
+  function stopSelectionWatch() {
+    state.coverage.stopSelectionWatch?.();
+    state.coverage.stopSelectionWatch = null;
+  }
+
+  /**
+   * Sequences (or overview points) drawn. A sequence that crosses a tile
+   * edge is in both tiles' lists, so sequences count once by id.
+   */
+  function sequenceCount() {
+    const ids = new Set();
+    let points = 0;
+    for (const entry of state.coverage.tiles.values())
+      if (entry.kind === 'sequence')
+        for (const id of entry.sequences.keys()) ids.add(id);
+      else points += entry.count;
+    return ids.size + points;
+  }
+
+  return {
+    attach,
+    detach,
+    refresh,
+    clear,
+    resetErrors,
+    rebuild,
+    reload,
+    setSurface,
+    recolorSequence,
+    sequenceCount,
+  };
+}

src/layers/streetLevel/lineCoverage.test.mjs

@@ -0,0 +1,142 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { createLineCoverage } from './lineCoverage.js';
+import {
+  coverageViewer,
+  tileCentre,
+} from '../../testSupport/streetLevelFakes.mjs';
+import { until } from '../../testSupport/kartaViewFakes.mjs';
+
+const TUNING = Object.freeze({
+  maxTiles: 9,
+  overviewMaxTiles: 0,
+  maxSequences: 900,
+  lineWidthPx: 2,
+  overviewPointPx: 2,
+  moveDebounceMs: 10,
+  viewRangeMinM: 2_500,
+  viewRangePerHeight: 10,
+  viewNearM: 1_000,
+});
+
+/**
+ * Line coverage over one tile holding one line, on a viewer looking down from
+ * `height`. `fetchTile` answers with that line unless `fail` says otherwise.
+ */
+function setup(
+  t,
+  { zoomFor, messages = { rateLimited: 'busy' }, passes, fail } = {},
+) {
+  const centre = tileCentre(-121.4944, 38.5816);
+  const viewer = coverageViewer(
+    { lon: centre.lon, lat: centre.lat, height: 900 },
+    t,
+  );
+  const state = {
+    viewer,
+    services: {},
+    keyRequired: false,
+    keyRejected: false,
+    context: {
+      getFilter: () => ({ pano: 'all', sinceMs: null }),
+      isActive: () => true,
+      notify() {},
+      getSurface: () => 'draped',
+      groundCaster: null,
+      meshSampler: null,
+    },
+    coverage: {
+      zoom: null,
+      kind: null,
+      tiles: new Map(),
+      stale: new Map(),
+      staleTimer: null,
+      pending: new Map(),
+      lastError: null,
+      holdUntil: 0,
+      holdTimer: null,
+      debounceTimer: null,
+      removeCameraListener: null,
+      terrainReady: Promise.resolve(),
+      hint: '',
+    },
+    sequence: { selectedId: null },
+  };
+  const asked = [];
+  const coverage = createLineCoverage({
+    state,
+    fetchTile: async (tile) => {
+      asked.push(tile);
+      if (fail) throw fail;
+      return {
+        sequences: [
+          {
+            id: 'line-1',
+            parts: [
+              [
+                [centre.lon - 0.001, centre.lat],
+                [centre.lon + 0.001, centre.lat],
+              ],
+            ],
+            capturedAt: 0,
+            isPano: false,
+          },
+        ],
+        overview: [],
+      };
+    },
+    zoomFor:
+      zoomFor ??
+      ((height) =>
+        Number.isFinite(height) && height <= 6_000
+          ? { zoom: 14, kind: 'sequence' }
+          : null),
+    colors: { coverage: '#635bff', selected: '#00e5ff' },
+    pickPrefix: 'test:line:',
+    renderKey: 'test-coverage',
+    tuning: TUNING,
+    messages,
+    ...(passes ? { passes } : {}),
+  });
+  t.after(() => {
+    coverage.clear();
+    coverage.resetErrors();
+  });
+  return { viewer, state, coverage, asked };
+}
+
+test('above the zoom range the provider’s own “zoom in” hint shows; without one, the generic hint', (t) => {
+  const tooHigh = 'zoom in to see test coverage';
+  const high = setup(t, { messages: { rateLimited: 'busy', tooHigh } });
+  high.viewer.view.height = 7_000;
+  high.coverage.refresh();
+  assert.equal(high.state.coverage.hint, tooHigh);
+  assert.equal(high.state.coverage.zoom, null);
+  assert.equal(high.asked.length, 0, 'nothing is asked from up there');
+  const generic = setup(t);
+  generic.viewer.view.height = 7_000;
+  generic.coverage.refresh();
+  assert.notEqual(generic.state.coverage.hint, tooHigh);
+  assert.match(generic.state.coverage.hint, /Point the camera/);
+});
+
+test('a provider’s passes() decides which lines are drawn and counted', async (t) => {
+  const all = setup(t, { passes: () => true });
+  all.coverage.refresh();
+  assert.ok(await until(() => all.state.coverage.tiles.size === 1));
+  assert.equal(all.coverage.sequenceCount(), 1, 'control: the line is drawn');
+  const none = setup(t, { passes: () => false });
+  none.coverage.refresh();
+  assert.ok(await until(() => none.state.coverage.tiles.size === 1));
+  assert.equal(none.coverage.sequenceCount(), 0, 'filtered out');
+});
+
+test('a refused key without its own message keeps the error it came with', async (t) => {
+  const refused = Object.assign(new Error('the source refused the key'), {
+    keyRejected: true,
+  });
+  const { state, coverage } = setup(t, { fail: refused });
+  coverage.refresh();
+  assert.ok(await until(() => state.keyRejected === true));
+  assert.equal(state.coverage.lastError, 'the source refused the key');
+});

src/layers/streetLevel/policy.js

@@ -8,6 +8,7 @@ export const POSITION_PICK_ID = 'sl:pos';
 export const PROVIDER_COLORS = Object.freeze({
   mapillary: '#05cb63',
   google: '#4285f4',
+  kartaview: '#635bff',
 });
 
 /** Colours every provider shares: the selection highlight and the marker. */

src/layers/streetLevel/providers/kartaview/decode.js

@@ -0,0 +1,176 @@
+import { MASK_KEEP_SHARE, MASK_SAMPLE_PX } from './policy.js';
+
+/** More than any real tile holds (a dense z13 tile has ~4,700 segments). */
+export const MAX_TILE_SEGMENTS = 20_000;
+/** A chained line stops growing here and the next one starts. */
+export const MAX_LINE_POINTS = 5_000;
+
+/**
+ * The way segments of a KartaView coverage tile
+ * (`{lines: [{track: [{lat, lng}]}]}`), as [lon, lat] point lists. Lines
+ * carry no sequence, date or projection: a filter thins them through a mask
+ * (see `maskedSegments`).
+ * @param {object} payload
+ * @returns {Array<Array<[number, number]>>}
+ */
+export function tileSegments(payload) {
+  // Not cached as empty: an unreadable tile is asked for again.
+  if (!Array.isArray(payload?.lines))
+    throw new Error('KartaView sent an unreadable coverage tile');
+  const segments = [];
+  for (const line of payload.lines) {
+    if (segments.length >= MAX_TILE_SEGMENTS) break;
+    const points = [];
+    for (const point of Array.isArray(line?.track) ? line.track : []) {
+      const lon = Number(point?.lng);
+      const lat = Number(point?.lat);
+      if (!Number.isFinite(lon) || !Number.isFinite(lat)) continue;
+      const last = points[points.length - 1];
+      if (last && last[0] === lon && last[1] === lat) continue;
+      points.push([lon, lat]);
+    }
+    if (points.length >= 2) segments.push(points);
+  }
+  return segments;
+}
+
+/**
+ * Segments chained into line records for the shared coverage: segments
+ * that meet end to start are joined, which cuts the line count about
+ * fourfold.
+ * @param {Array<Array<[number, number]>>} segments
+ * @param {{x: number, y: number, z: number}} address
+ * @returns {{sequences: Array<{id: string, parts: Array<Array<[number, number]>>, capturedAt: number, isPano: boolean}>, overview: Array<never>}}
+ */
+export function chainSegments(segments, { x, y, z }) {
+  const key = ([lon, lat]) => `${lon},${lat}`;
+  const startingAt = new Map();
+  segments.forEach((segment, index) => {
+    const at = key(segment[0]);
+    const list = startingAt.get(at);
+    if (list) list.push(index);
+    else startingAt.set(at, [index]);
+  });
+  const used = new Uint8Array(segments.length);
+  // Per start point, how far its list has been used: each segment is looked
+  // at once, so a tile of segments sharing one point stays linear.
+  const cursor = new Map();
+  const nextFrom = (point) => {
+    const at = key(point);
+    const list = startingAt.get(at);
+    if (!list) return undefined;
+    let i = cursor.get(at) ?? 0;
+    while (i < list.length && used[list[i]]) i++;
+    cursor.set(at, i);
+    return list[i];
+  };
+  const sequences = [];
+  segments.forEach((segment, index) => {
+    if (used[index]) return;
+    used[index] = 1;
+    const chain = [...segment];
+    for (;;) {
+      const next = nextFrom(chain[chain.length - 1]);
+      if (next === undefined) break;
+      // Full: the segment starts the next line instead.
+      if (chain.length + segments[next].length - 1 > MAX_LINE_POINTS) break;
+      used[next] = 1;
+      chain.push(...segments[next].slice(1));
+    }
+    sequences.push({
+      id: `${z}/${x}/${y}/${sequences.length}`,
+      parts: [chain],
+      capturedAt: 0,
+      isPano: false,
+    });
+  });
+  return { sequences, overview: [] };
+}
+
+/** Decode a KartaView coverage tile into the shared coverage's line records. */
+export function decodeCoverageTile(payload, address) {
+  return chainSegments(tileSegments(payload), address);
+}
+
+/**
+ * The segments a filtered PNG tile of the same address draws over. The PNG
+ * draws the same ways a few pixels wide (on a transparent ground): a
+ * segment is kept when at least half the points sampled along it have a
+ * drawn pixel within one pixel. Segments either lie on it or miss it
+ * almost entirely (Jakarta, 360° only: 332 of 1,041 kept, 676 missed, 33
+ * between). A segment with no point on the tile is not this tile's to keep.
+ * @param {Array<Array<[number, number]>>} segments
+ * @param {{width: number, height: number, alpha: ArrayLike<number>}} mask  one alpha byte per pixel
+ * @param {{x: number, y: number, z: number}} address
+ */
+export function maskedSegments(segments, mask, { x, y, z }) {
+  const { width, height, alpha } = mask;
+  const n = 2 ** z;
+  const toPixel = ([lon, lat]) => {
+    const sin = Math.sin((lat * Math.PI) / 180);
+    const my = 0.5 - Math.log((1 + sin) / (1 - sin)) / (4 * Math.PI);
+    return [(((lon + 180) / 360) * n - x) * width, (my * n - y) * height];
+  };
+  const drawnNear = (px, py) => {
+    const cx = Math.floor(px);
+    const cy = Math.floor(py);
+    for (let dy = -1; dy <= 1; dy++)
+      for (let dx = -1; dx <= 1; dx++) {
+        const X = cx + dx;
+        const Y = cy + dy;
+        if (X < 0 || Y < 0 || X >= width || Y >= height) continue;
+        if (alpha[Y * width + X] > 0) return true;
+      }
+    return false;
+  };
+  return segments.filter((segment) => {
+    let on = 0;
+    let tested = 0;
+    let [ax, ay] = toPixel(segment[0]);
+    for (let i = 1; i < segment.length; i++) {
+      const [bx, by] = toPixel(segment[i]);
+      const steps = Math.max(
+        1,
+        Math.ceil(Math.hypot(bx - ax, by - ay) / MASK_SAMPLE_PX),
+      );
+      // Each point once: a segment's next stretch starts where this one ends.
+      for (let j = i === 1 ? 0 : 1; j <= steps; j++) {
+        const px = ax + ((bx - ax) * j) / steps;
+        const py = ay + ((by - ay) * j) / steps;
+        if (px < 0 || py < 0 || px >= width || py >= height) continue;
+        tested++;
+        if (drawnNear(px, py)) on++;
+      }
+      ax = bx;
+      ay = by;
+    }
+    return tested > 0 && on / tested >= MASK_KEEP_SHARE;
+  });
+}
+
+/**
+ * A PNG mask's alpha, one byte per pixel, decoded off the main thread
+ * where the browser can.
+ * @param {Uint8Array} bytes  the PNG
+ * @returns {Promise<{width: number, height: number, alpha: Uint8Array}>}
+ */
+export async function readMaskImage(bytes) {
+  const bitmap = await createImageBitmap(
+    new Blob([bytes], { type: 'image/png' }),
+  );
+  try {
+    const { width, height } = bitmap;
+    const canvas =
+      typeof OffscreenCanvas === 'function'
+        ? new OffscreenCanvas(width, height)
+        : Object.assign(document.createElement('canvas'), { width, height });
+    const context = canvas.getContext('2d', { willReadFrequently: true });
+    context.drawImage(bitmap, 0, 0);
+    const rgba = context.getImageData(0, 0, width, height).data;
+    const alpha = new Uint8Array(width * height);
+    for (let i = 0; i < alpha.length; i++) alpha[i] = rgba[i * 4 + 3];
+    return { width, height, alpha };
+  } finally {
+    bitmap.close?.();
+  }
+}

src/layers/streetLevel/providers/kartaview/decode.test.mjs

@@ -0,0 +1,187 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import {
+  MAX_LINE_POINTS,
+  MAX_TILE_SEGMENTS,
+  chainSegments,
+  decodeCoverageTile,
+  maskedSegments,
+  tileSegments,
+} from './decode.js';
+
+const at = (lng, lat) => ({ lat: String(lat), lng: String(lng) });
+const TILE = { x: 4412, y: 6061, z: 14 };
+
+test('segments that meet end to start chain into one line', () => {
+  const { sequences, overview } = decodeCoverageTile(
+    {
+      lines: [
+        { track: [at(1, 1), at(2, 1)], matched: '1' },
+        { track: [at(5, 5), at(6, 6)], matched: '1' },
+        { track: [at(2, 1), at(3, 1), at(4, 2)], matched: '1' },
+      ],
+    },
+    TILE,
+  );
+  assert.deepEqual(overview, []);
+  assert.equal(sequences.length, 2);
+  assert.deepEqual(sequences[0].parts, [
+    [
+      [1, 1],
+      [2, 1],
+      [3, 1],
+      [4, 2],
+    ],
+  ]);
+  assert.equal(sequences[0].id, '14/4412/6061/0');
+  assert.equal(sequences[1].id, '14/4412/6061/1');
+  // Nothing to date or project: every line passes as flat and undated.
+  assert.equal(sequences[0].capturedAt, 0);
+  assert.equal(sequences[0].isPano, false);
+});
+
+test('a junction continues one way only, and every segment is drawn exactly once', () => {
+  const { sequences } = decodeCoverageTile(
+    {
+      lines: [
+        { track: [at(0, 0), at(1, 0)] },
+        { track: [at(1, 0), at(2, 0)] },
+        { track: [at(1, 0), at(1, 1)] },
+        // A loop back to its own start must end, not spin.
+        { track: [at(9, 9), at(9, 8)] },
+        { track: [at(9, 8), at(9, 9)] },
+      ],
+    },
+    TILE,
+  );
+  const points = sequences.reduce((sum, s) => sum + s.parts[0].length, 0);
+  assert.equal(sequences.length, 3);
+  // 5 segments of 2 points, 2 joins in chains: 10 - 2 = 8 points.
+  assert.equal(points, 8);
+});
+
+test('bad points, repeats and one-point tracks are skipped; an empty tile has no lines', () => {
+  const { sequences } = decodeCoverageTile(
+    {
+      lines: [
+        { track: [at(1, 1), at(1, 1), { lat: 'x', lng: '2' }, at(2, 2)] },
+        { track: [at(3, 3)] },
+        { track: null },
+        null,
+      ],
+    },
+    TILE,
+  );
+  assert.equal(sequences.length, 1);
+  assert.deepEqual(sequences[0].parts[0], [
+    [1, 1],
+    [2, 2],
+  ]);
+  assert.deepEqual(decodeCoverageTile({ lines: [] }, TILE).sequences, []);
+});
+
+test('a tile that is not a line list fails, so it is asked for again rather than kept empty', () => {
+  for (const payload of [
+    null,
+    {},
+    { lines: 'nope' },
+    { status: { apiCode: 690 } },
+  ])
+    assert.throws(
+      () => decodeCoverageTile(payload, TILE),
+      /unreadable coverage tile/,
+    );
+});
+
+test('a tile whose segments all share one point decodes in linear time', () => {
+  // [P, Q_i, P]: every chain step looks at the same start point's list.
+  // 60k: the old quadratic chaining took over a second; capped and linear
+  // decoding takes tens of milliseconds.
+  const lines = Array.from({ length: 60_000 }, (_, i) => ({
+    track: [at(0, 0), at(1 + i * 1e-6, 1), at(0, 0)],
+  }));
+  const started = performance.now();
+  const { sequences } = decodeCoverageTile({ lines }, TILE);
+  const ms = performance.now() - started;
+  assert.ok(
+    ms < 1_000,
+    `${Math.round(ms)} ms (quadratic chaining took ~200 ms per 20k and grows fourfold per doubling)`,
+  );
+  const points = sequences.reduce((sum, s) => sum + s.parts[0].length, 0);
+  assert.ok(sequences.every((s) => s.parts[0].length <= MAX_LINE_POINTS));
+  assert.equal(
+    points,
+    MAX_TILE_SEGMENTS * 2 + sequences.length,
+    'every segment drawn once',
+  );
+});
+
+test('a tile is capped in segments and in points per line', () => {
+  const lines = Array.from({ length: MAX_TILE_SEGMENTS + 500 }, (_, i) => ({
+    track: [at(i, 0), at(i + 1, 0)],
+  }));
+  const { sequences } = decodeCoverageTile({ lines }, TILE);
+  const points = sequences.reduce((sum, s) => sum + s.parts[0].length, 0);
+  // One long chain, cut into lines of at most MAX_LINE_POINTS.
+  assert.ok(sequences.every((s) => s.parts[0].length <= MAX_LINE_POINTS));
+  assert.ok(points <= MAX_TILE_SEGMENTS + sequences.length);
+  assert.ok(
+    sequences.length >= Math.floor(MAX_TILE_SEGMENTS / MAX_LINE_POINTS),
+  );
+});
+
+/** [lon, lat] at pixel (px, py) of a 512 px mask of `tile` (Web Mercator). */
+function lonLatAt(px, py, { x, y, z } = TILE, size = 512) {
+  const n = 2 ** z;
+  const lon = ((x + px / size) / n) * 360 - 180;
+  const my = Math.PI * (1 - (2 * (y + py / size)) / n);
+  const lat = (Math.atan(Math.sinh(my)) * 180) / Math.PI;
+  return [lon, lat];
+}
+
+/** A 512 px mask drawn on the given rows. */
+function rowsMask(rows) {
+  const alpha = new Uint8Array(512 * 512);
+  for (const [from, to] of rows) alpha.fill(255, from * 512, (to + 1) * 512);
+  return { width: 512, height: 512, alpha };
+}
+
+test('a mask keeps the segments it draws over, chained as before', () => {
+  const along = (row, from = 40, to = 470) => [
+    lonLatAt(from, row),
+    lonLatAt(to, row),
+  ];
+  const segments = [
+    along(100), // drawn at row 100
+    along(101.6), // a pixel off: still drawn within one pixel
+    along(300), // not drawn
+    // Two thirds along the drawn row, then off it: kept (at least half).
+    [lonLatAt(40, 100), lonLatAt(400, 100), lonLatAt(400, 280)],
+    // A third along it, then off: dropped.
+    [lonLatAt(300, 100), lonLatAt(400, 100), lonLatAt(400, 300)],
+    // Off the tile entirely: not this tile's to keep.
+    [lonLatAt(-200, 100), lonLatAt(-20, 100)],
+  ];
+  const kept = maskedSegments(segments, rowsMask([[99, 100]]), TILE);
+  assert.deepEqual(kept, [segments[0], segments[1], segments[3]]);
+  assert.deepEqual(maskedSegments(segments, rowsMask([]), TILE), []);
+  // A full mask keeps every segment that is on the tile.
+  assert.equal(maskedSegments(segments, rowsMask([[0, 511]]), TILE).length, 5);
+});
+
+test('decoding is segments then chaining: the same lines either way', () => {
+  const payload = {
+    lines: [
+      { track: [at(1, 1), at(2, 1)] },
+      { track: [at(2, 1), at(3, 1)] },
+      { track: [at(5, 5), at(6, 6)] },
+    ],
+  };
+  const segments = tileSegments(payload);
+  assert.equal(segments.length, 3);
+  assert.deepEqual(
+    chainSegments(segments, TILE),
+    decodeCoverageTile(payload, TILE),
+  );
+  assert.throws(() => tileSegments({}), /unreadable coverage tile/);
+});

src/layers/streetLevel/providers/kartaview/index.js

@@ -0,0 +1,649 @@
+import { createLineCoverage } from '../../lineCoverage.js';
+import { createSequenceCones, thinImages } from '../../sequenceCones.js';
+import { metresBetween } from '../../view.js';
+import {
+  chainSegments,
+  maskedSegments,
+  readMaskImage,
+  tileSegments,
+} from './decode.js';
+import { createKartaViewSource } from './source.js';
+import { createKartaViewViewer } from './viewer.js';
+import {
+  ARCHIVED_MESSAGE,
+  COLORS,
+  COVERAGE_MAX_HEIGHT_M,
+  COVERAGE_NOUN,
+  COVERAGE_STREET_ZOOM_BELOW_M,
+  COVERAGE_TUNING,
+  FILTERED_OUT_MESSAGE,
+  KARTAVIEW_CREDIT_HTML,
+  KARTAVIEW_LABEL,
+  KARTAVIEW_NAME,
+  KARTAVIEW_PROVIDER_ID,
+  LINE_CLICK_HINT,
+  NEAREST_PROBES,
+  NEAREST_RADIUS_M,
+  NO_COVERAGE_HINT,
+  PICK_PREFIX,
+  RATE_LIMITED_MESSAGE,
+  SEQUENCE_PAGE_EDGE,
+  SEQUENCE_PAGE_SIZE,
+  TOO_HIGH_HINT,
+  assignCourses,
+  cameraBearing,
+  normalizePhoto,
+  passesKartaViewFilter,
+  tileFilterQuery,
+} from './policy.js';
+
+/** Photos kept in memory by id (sequence pages fill it). */
+const PHOTO_CACHE_SIZE = 4000;
+/** Sequence pages kept in memory. */
+const PAGE_CACHE_SIZE = 12;
+/** Decoded coverage tiles kept, and for how long (masks too). */
+const TILE_CACHE_SIZE = 24;
+const TILE_CACHE_TTL_MS = 10 * 60_000;
+
+/** z14 near the street, z13 a little higher, nothing above. */
+export function kartaViewZoomFor(heightM) {
+  if (!Number.isFinite(heightM) || heightM > COVERAGE_MAX_HEIGHT_M) return null;
+  return {
+    zoom: heightM > COVERAGE_STREET_ZOOM_BELOW_M ? 13 : 14,
+    kind: 'sequence',
+  };
+}
+
+/** Least-recently-used map: reading an entry renews it. */
+function createLru(limit) {
+  const map = new Map();
+  return {
+    get(key) {
+      if (!map.has(key)) return undefined;
+      const value = map.get(key);
+      map.delete(key);
+      map.set(key, value);
+      return value;
+    },
+    set(key, value) {
+      map.delete(key);
+      map.set(key, value);
+      while (map.size > limit) map.delete(map.keys().next().value);
+    },
+    delete: (key) => map.delete(key),
+    clear: () => map.clear(),
+  };
+}
+
+/**
+ * Loaded coverage tiles by `z/x/y`, at most `size`, each for `ttlMs`. KartaView
+ * sends tiles uncompressed and uncacheable (hundreds of kB, seconds each), so
+ * a pan back or a zoom across z13/z14 would fetch them all again.
+ */
+export function createTileCache({
+  load,
+  size = TILE_CACHE_SIZE,
+  ttlMs = TILE_CACHE_TTL_MS,
+  now = Date.now,
+  keyOf = (tile) => `${tile.z}/${tile.x}/${tile.y}`,
+}) {
+  const kept = createLru(size);
+  return {
+    async get(tile, options) {
+      const key = keyOf(tile);
+      const entry = kept.get(key);
+      if (entry && now() - entry.at < ttlMs) return entry.tile;
+      const loaded = await load(tile, options);
+      kept.set(key, { at: now(), tile: loaded });
+      return loaded;
+    },
+    /** Drop every tile (the provider was switched off). */
+    clear: () => kept.clear(),
+  };
+}
+
+/** The 1-based page of a sequence that holds `index`, if no photo is missing. */
+function pageOf(index) {
+  return Math.floor(Math.max(0, index) / SEQUENCE_PAGE_SIZE) + 1;
+}
+
+/**
+ * KartaView Street Level provider: keyless coverage lines from KartaView's
+ * tile API, the photos nearest a clicked line, cones along the photo's
+ * sequence, and a flat or 360° viewer with ‹ › along the sequence.
+ * @param {{source?: ReturnType<typeof createKartaViewSource>, viewerOptions?: object, readMask?: typeof readMaskImage}} [options]
+ * @returns {import('../../registry.js').StreetLevelProvider}
+ */
+export function createKartaViewProvider({
+  source = createKartaViewSource(),
+  viewerOptions = {},
+  readMask = readMaskImage,
+} = {}) {
+  return Object.freeze({
+    id: KARTAVIEW_PROVIDER_ID,
+    name: KARTAVIEW_NAME,
+    label: KARTAVIEW_LABEL,
+    requiresKeyId: null,
+    pickPrefix: PICK_PREFIX.root,
+    colors: COLORS,
+    // Its own marker, as Street View has: a purple cone that turns with the view.
+    marker: Object.freeze({ kind: 'view-cone', color: COLORS.coverage }),
+    credit: Object.freeze({ html: KARTAVIEW_CREDIT_HTML }),
+    defaultOn: false,
+    // 360° / flat and SINCE, as Mapillary: KartaView filters the lines on
+    // its server (see tileFilterQuery), the photos by their own record.
+    filters: Object.freeze(['pano', 'since']),
+    // SINCE is the upload date for KartaView: the panel notes it.
+    sinceBasis: 'upload',
+    // Its lines are streets, not sequences: a selected drive shows as cones.
+    highlightsSequence: false,
+    coverageLabel: Object.freeze({
+      noun: COVERAGE_NOUN,
+      action: LINE_CLICK_HINT,
+    }),
+
+    create(context) {
+      const state = {
+        context,
+        services: context.services,
+        viewer: null,
+        keyRequired: false,
+        keyRejected: false,
+        statusKnown: true,
+        coverage: {
+          zoom: null,
+          tiles: new Map(),
+          stale: new Map(),
+          staleTimer: null,
+          pending: new Map(),
+          lastError: null,
+          holdUntil: 0,
+          holdTimer: null,
+          debounceTimer: null,
+          removeCameraListener: null,
+          terrainReady: null,
+          hint: '',
+          kind: null,
+        },
+        sequence: {
+          selectedId: null,
+          images: [],
+          cache: new Map(),
+          collection: null,
+          loading: false,
+          abort: null,
+        },
+      };
+      const photos = createLru(PHOTO_CACHE_SIZE);
+      const pages = createLru(PAGE_CACHE_SIZE);
+      /** The photo last opened in each sequence: its cones centre on it. */
+      const anchors = new Map();
+      /** The sequence page the cones were drawn from. */
+      let drawnPage = null;
+
+      /** A record as a photo; the one already known keeps its identity (and course). */
+      function remember(record) {
+        const fresh = normalizePhoto(record);
+        if (!fresh) return null;
+        const known = photos.get(fresh.id);
+        const photo = known ? Object.assign(known, fresh) : fresh;
+        photos.set(photo.id, photo);
+        return photo;
+      }
+
+      async function getPhoto(photoId, { signal } = {}) {
+        const cached = photos.get(photoId);
+        if (cached) return cached;
+        const photo = remember(await source.getPhoto(photoId, { signal }));
+        if (!photo) throw new Error('KartaView has no position for this photo');
+        return photo;
+      }
+
+      /** A page of a sequence's photos, in index order (shared while in flight). */
+      function loadPage(sequenceId, page) {
+        const key = `${sequenceId}:${page}`;
+        let entry = pages.get(key);
+        if (!entry) {
+          entry = source
+            .getSequencePhotos(sequenceId, {
+              page,
+              itemsPerPage: SEQUENCE_PAGE_SIZE,
+            })
+            .then(({ photos: records, hasMore }) => {
+              const list = assignCourses(
+                records
+                  .map(remember)
+                  .filter(Boolean)
+                  .sort(
+                    (a, b) => (a.sequenceIndex ?? 0) - (b.sequenceIndex ?? 0),
+                  ),
+                metresBetween,
+              );
+              // The open photo may have just learnt which way it looked. The
+              // page is good whatever the viewer is doing.
+              try {
+                viewer.refreshPose?.();
+              } catch {
+                /* the next pose carries the direction */
+              }
+              return { page, hasMore, photos: list };
+            });
+          pages.set(key, entry);
+          entry.catch(() => pages.delete(key));
+        }
+        return entry;
+      }
+
+      /**
+       * The page holding `photo`. Pages follow photo ids, which only roughly
+       * follow the index, and photos go missing, so the page the index
+       * suggests is a first guess: step towards the photo until a page holds
+       * it, or the pages straddle where it would be.
+       */
+      async function homePage(photo) {
+        let number = pageOf(photo.sequenceIndex ?? 0);
+        const index = photo.sequenceIndex ?? 0;
+        let page = await loadPage(photo.sequenceId, number);
+        if (!page.photos.length && number > 1) {
+          // Past the end (many photos deleted): find the last page by halving.
+          let low = 1;
+          let high = number - 1;
+          while (low < high) {
+            const middle = Math.ceil((low + high) / 2);
+            if ((await loadPage(photo.sequenceId, middle)).photos.length)
+              low = middle;
+            else high = middle - 1;
+          }
+          number = low;
+        }
+        const seen = new Set();
+        while (!seen.has(number) && seen.size < 8) {
+          seen.add(number);
+          page = await loadPage(photo.sequenceId, number);
+          if (page.photos.some((p) => p.id === photo.id)) return page;
+          const first = page.photos[0]?.sequenceIndex;
+          const last = page.photos.at(-1)?.sequenceIndex;
+          // Past the last page, or before this page's photos: go back.
+          if ((first === undefined || index < first) && number > 1) number--;
+          else if (last !== undefined && index > last && page.hasMore) number++;
+          else break;
+        }
+        return page;
+      }
+
+      /**
+       * The photos around `photo` in index order: its page, plus a
+       * neighbour page when it sits near an edge (pages overlap in index).
+       * @returns {Promise<{home: number, photos: Array<object>}>}
+       */
+      async function windowOf(photo) {
+        const home = await homePage(photo);
+        const list = home.photos;
+        const found = list.findIndex((p) => p.id === photo.id);
+        // A photo no page lists sits where its index would.
+        const at =
+          found !== -1
+            ? found
+            : list.filter(
+                (p) => (p.sequenceIndex ?? 0) < (photo.sequenceIndex ?? 0),
+              ).length;
+        const parts = [list];
+        if (at < SEQUENCE_PAGE_EDGE && home.page > 1)
+          parts.push((await loadPage(photo.sequenceId, home.page - 1)).photos);
+        if (at >= list.length - SEQUENCE_PAGE_EDGE && home.hasMore)
+          parts.push((await loadPage(photo.sequenceId, home.page + 1)).photos);
+        if (parts.length === 1) return { home: home.page, photos: list };
+        const byId = new Map(parts.flat().map((p) => [p.id, p]));
+        return {
+          home: home.page,
+          photos: [...byId.values()].sort(
+            (a, b) => (a.sequenceIndex ?? 0) - (b.sequenceIndex ?? 0),
+          ),
+        };
+      }
+
+      /**
+       * Photo id → whether its file is there (archived ones are not). Only
+       * a definite answer is kept: a storage hiccup is asked again next
+       * time, and meanwhile the photo is tried. A probe is shared, so it
+       * runs to its own timeout rather than any one caller's abort.
+       */
+      const probes = createLru(PHOTO_CACHE_SIZE);
+      function showable(photo) {
+        if (!photo?.urls?.view) return Promise.resolve(false);
+        let probe = probes.get(photo.id);
+        if (!probe) {
+          probe = source.probeImage(photo.urls.view).then(
+            (answer) => {
+              if (answer === null) probes.delete(photo.id);
+              return answer !== false;
+            },
+            () => {
+              probes.delete(photo.id);
+              return true;
+            },
+          );
+          probes.set(photo.id, probe);
+        }
+        return probe;
+      }
+
+      // A tile's way segments, kept a while: panning back, or a filter
+      // change, asks KartaView nothing more for them.
+      const tiles = createTileCache({
+        load: async (tile, { signal }) =>
+          tileSegments(await source.getTile(tile, { signal })),
+      });
+      // A filtered tile's mask, by filter and tile.
+      const masks = createTileCache({
+        load: async ({ query, ...tile }, { signal }) =>
+          readMask(await source.getTileMask(tile, query, { signal })),
+        keyOf: ({ query, z, x, y }) => `${query}|${z}/${x}/${y}`,
+      });
+      /** The tile's lines under the filter now: all, or the masked ones. */
+      async function fetchTile(tile, options) {
+        const query = tileFilterQuery(context.getFilter());
+        if (!query) return chainSegments(await tiles.get(tile, options), tile);
+        const [segments, mask] = await Promise.all([
+          tiles.get(tile, options),
+          masks.get({ ...tile, query }, options),
+        ]);
+        return chainSegments(maskedSegments(segments, mask, tile), tile);
+      }
+      /** The query the drawn lines were loaded under. */
+      let drawnQuery = tileFilterQuery(context.getFilter());
+
+      /**
+       * The next showable photo `delta` along the sequence, or null at its
+       * end. Archived photos are skipped, a few at most.
+       */
+      async function step(photo, delta) {
+        if (!photo?.sequenceId) return null;
+        let from = photo;
+        for (let skipped = 0; skipped <= NEAREST_PROBES; skipped++) {
+          const { photos: list } = await windowOf(from);
+          let at = list.findIndex((p) => p.id === from.id);
+          if (at === -1) {
+            // Not found anywhere: the nearest index on the right side.
+            const index = from.sequenceIndex ?? 0;
+            const later = list.findIndex((p) => (p.sequenceIndex ?? 0) > index);
+            if (delta > 0 && later === -1) return null;
+            at =
+              delta > 0
+                ? later - 1
+                : later === -1
+                  ? list.length
+                  : list.findIndex((p) => (p.sequenceIndex ?? 0) >= index);
+          }
+          const next = list[at + delta];
+          if (!next) return null;
+          if (await showable(next)) return next.id;
+          from = next;
+        }
+        return null;
+      }
+
+      const coverage = createLineCoverage({
+        state,
+        fetchTile,
+        zoomFor: kartaViewZoomFor,
+        colors: COLORS,
+        pickPrefix: PICK_PREFIX.line,
+        renderKey: 'kartaview-coverage',
+        tuning: COVERAGE_TUNING,
+        messages: { rateLimited: RATE_LIMITED_MESSAGE, tooHigh: TOO_HIGH_HINT },
+        // Filtered on the way in (fetchTile): a line has no date to test.
+        passes: () => true,
+      });
+
+      const cones = createSequenceCones({
+        state,
+        async loadImages(sequenceId, { signal }) {
+          let anchor = anchors.get(sequenceId);
+          if (!anchor) return [];
+          let window = await windowOf(anchor);
+          signal?.throwIfAborted();
+          // Another photo of the drive opened while that page loaded (its
+          // re-centre found nothing drawn yet): centre on the newest one.
+          while (anchors.get(sequenceId) !== anchor) {
+            anchor = anchors.get(sequenceId);
+            window = await windowOf(anchor);
+            signal?.throwIfAborted();
+          }
+          drawnPage = { sequenceId, page: window.home };
+          countPhotos(sequenceId);
+          return thinImages(
+            window.photos.map((photo) => ({
+              id: photo.id,
+              lon: photo.lon,
+              lat: photo.lat,
+              compassAngle: cameraBearing(photo) ?? 0,
+              capturedAt: photo.capturedAt ?? 0,
+              uploadedAt: photo.uploadedAt,
+              isPano: photo.isPano,
+            })),
+          );
+        },
+        colors: COLORS,
+        pickPrefix: PICK_PREFIX.image,
+        spriteId: 'street-level:kartaview-cones',
+        renderKey: 'kartaview-sequence',
+        // By projection and upload date, as the lines.
+        passes: passesKartaViewFilter,
+      });
+
+      /** Sequence id → its photo count from KartaView (asked once). */
+      const counts = new Map();
+      function countPhotos(sequenceId) {
+        if (counts.has(sequenceId) || !source.getSequenceCount) return;
+        counts.set(sequenceId, undefined);
+        source.getSequenceCount(sequenceId).then(
+          (count) => {
+            if (count === null) counts.delete(sequenceId);
+            else {
+              counts.set(sequenceId, count);
+              context.notify();
+            }
+          },
+          () => counts.delete(sequenceId),
+        );
+      }
+
+      /** ‹ › open through the core (loading, errors, cones), camera still. */
+      function openStepped(photoId) {
+        context.actions.openImage(photoId, { frame: false });
+      }
+
+      /**
+       * The cones show one page of a sequence: once a photo of the selected
+       * sequence opens on another page (‹ ›, a cone, a line), re-centre them.
+       */
+      async function recentreCones(photo) {
+        if (!photo?.sequenceId) return;
+        if (state.sequence.selectedId !== photo.sequenceId) return;
+        const drawn = drawnPage;
+        if (drawn?.sequenceId !== photo.sequenceId) return;
+        const window = await windowOf(photo).catch(() => null);
+        // Still the drawn page and the latest photo once the page is in.
+        if (
+          window &&
+          drawnPage === drawn &&
+          window.home !== drawn.page &&
+          anchors.get(photo.sequenceId) === photo
+        )
+          cones.select(photo.sequenceId, { force: true });
+      }
+
+      const viewer = createKartaViewViewer({
+        getPhoto: async (photoId) => {
+          const photo = await getPhoto(photoId);
+          if (photo.sequenceId) anchors.set(photo.sequenceId, photo);
+          return photo;
+        },
+        step,
+        onStep: openStepped,
+        onShown: recentreCones,
+        // After a GPU reset the same photo is drawn again by the viewer
+        // itself: going through the core would cancel a lookup the user
+        // started. A failure still shows.
+        onReopen: (photoId) =>
+          viewer
+            .open(photoId)
+            .catch((error) =>
+              context.actions.reportError(
+                error?.message || 'The KartaView photo could not be loaded',
+              ),
+            ),
+        render: context.services?.render,
+        ...viewerOptions,
+      });
+
+      return {
+        async status() {
+          return { configured: true };
+        },
+
+        init(cesiumViewer) {
+          state.viewer = cesiumViewer;
+          cones.ensureCollections(cesiumViewer);
+          cones.setVisible(false);
+        },
+
+        activate(cesiumViewer) {
+          state.viewer = cesiumViewer;
+          cones.setVisible(true);
+          coverage.attach(cesiumViewer);
+        },
+
+        deactivate() {
+          coverage.detach();
+          coverage.clear();
+          coverage.resetErrors();
+          cones.clearSelection();
+          cones.setVisible(false);
+          drawnPage = null;
+          // Tens of MB of decoded lines are not kept for a source left off.
+          tiles.clear();
+          masks.clear();
+        },
+
+        destroy(cesiumViewer) {
+          coverage.detach();
+          coverage.clear();
+          coverage.resetErrors();
+          cones.destroy(cesiumViewer);
+          tiles.clear();
+          masks.clear();
+        },
+
+        refreshCoverage: () => coverage.refresh(),
+
+        /**
+         * The filter changed: the lines come from KartaView again under it
+         * (the old ones show meanwhile), the cones are drawn again.
+         */
+        setFilter() {
+          const query = tileFilterQuery(context.getFilter());
+          if (query !== drawnQuery) {
+            drawnQuery = query;
+            coverage.reload();
+          }
+          cones.rerender();
+        },
+
+        setSurface() {
+          coverage.setSurface();
+          cones.rerender();
+        },
+
+        coverageStats() {
+          const { hint } = state.coverage;
+          const count = coverage.sequenceCount();
+          const loading = state.coverage.pending.size > 0;
+          const empty =
+            state.coverage.zoom !== null &&
+            !loading &&
+            count === 0 &&
+            !state.coverage.lastError;
+          return {
+            count,
+            zoom: state.coverage.zoom,
+            kind: state.coverage.kind,
+            loading,
+            hint: hint || (empty ? NO_COVERAGE_HINT : ''),
+            error: state.coverage.lastError,
+            keyRequired: false,
+            keyRejected: false,
+          };
+        },
+
+        /** A line opens the photo nearest the click; a cone opens its photo. */
+        handlePick(pickId, { groundPoint } = {}) {
+          if (pickId.startsWith(PICK_PREFIX.image)) {
+            context.actions.openImage(pickId.slice(PICK_PREFIX.image.length));
+            return true;
+          }
+          if (pickId.startsWith(PICK_PREFIX.line)) {
+            const point = groundPoint?.();
+            if (point) context.actions.openNearest(point);
+            return true;
+          }
+          return false;
+        },
+
+        // Never from the cache: it is keyed by sequence, the cones by page.
+        selectSequence: (sequenceId) =>
+          cones.select(sequenceId, { force: true }),
+        clearSequence: () => {
+          cones.clearSelection();
+          drawnPage = null;
+        },
+        // The drive's own count, not the thinned page of it the cones show.
+        sequenceStats: () => ({
+          selectedId: state.sequence.selectedId,
+          images:
+            counts.get(state.sequence.selectedId) ??
+            state.sequence.images.length,
+          loading: state.sequence.loading,
+        }),
+
+        /**
+         * The nearest photo within the search radius that can be shown, or
+         * null. Many photos are archived (their files answer 409) or have no
+         * file at all, so the nearest few are tried in turn.
+         */
+        async nearestImage({ lat, lon }, { signal } = {}) {
+          const filter = context.getFilter();
+          const records = await source.nearestPhotos(
+            { lat, lon, filter },
+            { signal },
+          );
+          const near = [];
+          let filteredOut = 0;
+          for (const record of records) {
+            const photo = remember(record);
+            if (!photo?.urls.view) continue;
+            const metres = metresBetween({ lat, lon }, photo);
+            if (metres > NEAREST_RADIUS_M) continue;
+            if (!passesKartaViewFilter(photo, filter)) filteredOut++;
+            else near.push({ photo, metres });
+          }
+          near.sort((a, b) => a.metres - b.metres);
+          // Probed side by side (photo storage is not the API host): the
+          // nearest one that answers wins.
+          const candidates = near.slice(0, NEAREST_PROBES);
+          const answers = await Promise.all(
+            candidates.map(({ photo }) => showable(photo, { signal })),
+          );
+          const hit = candidates.find((_, i) => answers[i]);
+          if (hit) return hit.photo.id;
+          if (near.length) throw new Error(ARCHIVED_MESSAGE);
+          if (filteredOut) throw new Error(FILTERED_OUT_MESSAGE);
+          return null;
+        },
+
+        viewer,
+      };
+    },
+  });
+}

src/layers/streetLevel/providers/kartaview/panorama.js

@@ -0,0 +1,243 @@
+/**
+ * A minimal equirectangular panorama renderer on WebGL: one full-screen
+ * triangle whose fragment shader turns each pixel's view ray into texture
+ * coordinates. The image centre is the camera's forward direction; yaw turns
+ * right from it, pitch looks up.
+ */
+
+export const PANO_FOV_DEFAULT_DEG = 80;
+export const PANO_FOV_MIN_DEG = 30;
+export const PANO_FOV_MAX_DEG = 100;
+export const PANO_PITCH_LIMIT_DEG = 85;
+
+const VERTEX = `
+attribute vec2 a_position;
+varying vec2 v_ndc;
+void main() {
+  v_ndc = a_position;
+  gl_Position = vec4(a_position, 0.0, 1.0);
+}`;
+
+const FRAGMENT = `
+precision highp float;
+uniform sampler2D u_image;
+uniform float u_yaw;
+uniform float u_pitch;
+uniform float u_tanHalfFov;
+uniform float u_aspect;
+varying vec2 v_ndc;
+const float PI = 3.141592653589793;
+void main() {
+  vec3 ray = normalize(vec3(v_ndc.x * u_tanHalfFov * u_aspect, v_ndc.y * u_tanHalfFov, -1.0));
+  float cp = cos(u_pitch), sp = sin(u_pitch);
+  ray = vec3(ray.x, ray.y * cp - ray.z * sp, ray.y * sp + ray.z * cp);
+  float cy = cos(u_yaw), sy = sin(u_yaw);
+  ray = vec3(ray.x * cy - ray.z * sy, ray.y, ray.x * sy + ray.z * cy);
+  float lon = atan(ray.x, -ray.z);
+  float lat = asin(clamp(ray.y, -1.0, 1.0));
+  gl_FragColor = texture2D(u_image, vec2(0.5 + lon / (2.0 * PI), 0.5 - lat / PI));
+}`;
+
+/** Wrap degrees into [0, 360). */
+export function wrapDegrees(value) {
+  return ((value % 360) + 360) % 360;
+}
+
+export function clampPitch(degrees) {
+  return Math.max(
+    -PANO_PITCH_LIMIT_DEG,
+    Math.min(PANO_PITCH_LIMIT_DEG, degrees),
+  );
+}
+
+export function clampFov(degrees) {
+  return Math.max(PANO_FOV_MIN_DEG, Math.min(PANO_FOV_MAX_DEG, degrees));
+}
+
+/**
+ * Texture coordinates the shader samples for a view ray, for tests and
+ * picking: `yaw`/`pitch` in degrees, the ray in camera space (x right, y up,
+ * z backward).
+ */
+export function rayToUv(ray, { yaw = 0, pitch = 0 } = {}) {
+  const p = (pitch * Math.PI) / 180;
+  const w = (yaw * Math.PI) / 180;
+  const length = Math.hypot(ray[0], ray[1], ray[2]) || 1;
+  let [x, y, z] = ray.map((v) => v / length);
+  [y, z] = [
+    y * Math.cos(p) - z * Math.sin(p),
+    y * Math.sin(p) + z * Math.cos(p),
+  ];
+  [x, z] = [
+    x * Math.cos(w) - z * Math.sin(w),
+    x * Math.sin(w) + z * Math.cos(w),
+  ];
+  const lon = Math.atan2(x, -z);
+  const lat = Math.asin(Math.max(-1, Math.min(1, y)));
+  return [0.5 + lon / (2 * Math.PI), 0.5 - lat / Math.PI];
+}
+
+function compile(gl, type, source) {
+  const shader = gl.createShader(type);
+  gl.shaderSource(shader, source);
+  gl.compileShader(shader);
+  if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
+    const log = gl.getShaderInfoLog(shader);
+    gl.deleteShader(shader);
+    throw new Error(`Panorama shader failed: ${log}`);
+  }
+  return shader;
+}
+
+const isPowerOfTwo = (n) => n > 0 && (n & (n - 1)) === 0;
+
+/**
+ * A panorama view on `canvas`. Throws when WebGL is unavailable, so the
+ * caller can fall back to a flat picture.
+ * @param {HTMLCanvasElement} canvas
+ * @returns {{setImage: (image: TexImageSource) => void, setView: (view: {yaw?: number, pitch?: number, fov?: number}) => void, getView: () => {yaw: number, pitch: number, fov: number}, resize: () => void, render: () => void, hasImage: () => boolean, destroy: () => void}}
+ */
+export function createPanoramaRenderer(canvas) {
+  const gl =
+    canvas.getContext('webgl', {
+      antialias: false,
+      depth: false,
+      preserveDrawingBuffer: false,
+    }) || canvas.getContext('experimental-webgl');
+  if (!gl) throw new Error('WebGL is unavailable');
+
+  const program = gl.createProgram();
+  gl.attachShader(program, compile(gl, gl.VERTEX_SHADER, VERTEX));
+  gl.attachShader(program, compile(gl, gl.FRAGMENT_SHADER, FRAGMENT));
+  gl.linkProgram(program);
+  if (!gl.getProgramParameter(program, gl.LINK_STATUS))
+    throw new Error('Panorama program failed to link');
+  gl.useProgram(program);
+
+  const buffer = gl.createBuffer();
+  gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
+  // One triangle covering the screen.
+  gl.bufferData(
+    gl.ARRAY_BUFFER,
+    new Float32Array([-1, -1, 3, -1, -1, 3]),
+    gl.STATIC_DRAW,
+  );
+  const position = gl.getAttribLocation(program, 'a_position');
+  gl.enableVertexAttribArray(position);
+  gl.vertexAttribPointer(position, 2, gl.FLOAT, false, 0, 0);
+  const uniforms = Object.fromEntries(
+    ['u_image', 'u_yaw', 'u_pitch', 'u_tanHalfFov', 'u_aspect'].map((name) => [
+      name,
+      gl.getUniformLocation(program, name),
+    ]),
+  );
+  const texture = gl.createTexture();
+  let loaded = false;
+  let frame = 0;
+  const view = { yaw: 0, pitch: 0, fov: PANO_FOV_DEFAULT_DEG };
+
+  /** Match the drawing buffer to the canvas's laid-out size. */
+  function syncSize() {
+    const ratio = Math.min(globalThis.devicePixelRatio || 1, 2);
+    const width = Math.max(1, Math.round(canvas.clientWidth * ratio));
+    const height = Math.max(1, Math.round(canvas.clientHeight * ratio));
+    if (canvas.width !== width || canvas.height !== height) {
+      canvas.width = width;
+      canvas.height = height;
+    }
+  }
+
+  function resize() {
+    syncSize();
+    scheduleRender();
+  }
+
+  function draw() {
+    frame = 0;
+    if (gl.isContextLost()) return;
+    // Every frame: the canvas may have been laid out since the last one.
+    syncSize();
+    gl.viewport(0, 0, canvas.width, canvas.height);
+    gl.clearColor(0, 0, 0, 1);
+    gl.clear(gl.COLOR_BUFFER_BIT);
+    if (!loaded) return;
+    gl.uniform1i(uniforms.u_image, 0);
+    gl.uniform1f(uniforms.u_yaw, (view.yaw * Math.PI) / 180);
+    gl.uniform1f(uniforms.u_pitch, (view.pitch * Math.PI) / 180);
+    gl.uniform1f(uniforms.u_tanHalfFov, Math.tan((view.fov * Math.PI) / 360));
+    gl.uniform1f(uniforms.u_aspect, canvas.width / Math.max(1, canvas.height));
+    gl.drawArrays(gl.TRIANGLES, 0, 3);
+  }
+
+  function scheduleRender() {
+    if (frame) return;
+    frame = requestAnimationFrame(draw);
+  }
+
+  return {
+    setImage(image) {
+      gl.activeTexture(gl.TEXTURE0);
+      gl.bindTexture(gl.TEXTURE_2D, texture);
+      gl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL, false);
+      // RGBA: the format a decoded ImageBitmap uploads without conversion.
+      gl.texImage2D(
+        gl.TEXTURE_2D,
+        0,
+        gl.RGBA,
+        gl.RGBA,
+        gl.UNSIGNED_BYTE,
+        image,
+      );
+      // The pixels are on the GPU now; a bitmap's copy can go.
+      image.close?.();
+      // Linear only: a mipmapped lookup draws a seam where longitude wraps.
+      gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
+      gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
+      const repeat =
+        isPowerOfTwo(image.width) && isPowerOfTwo(image.height)
+          ? gl.REPEAT
+          : gl.CLAMP_TO_EDGE;
+      gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, repeat);
+      gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
+      loaded = true;
+      resize();
+      scheduleRender();
+    },
+    setView(next = {}) {
+      if (Number.isFinite(next.yaw)) view.yaw = wrapDegrees(next.yaw);
+      if (Number.isFinite(next.pitch)) view.pitch = clampPitch(next.pitch);
+      if (Number.isFinite(next.fov)) view.fov = clampFov(next.fov);
+      scheduleRender();
+    },
+    getView: () => ({ ...view }),
+    resize,
+    render: scheduleRender,
+    hasImage: () => loaded,
+    clear() {
+      loaded = false;
+      // Hand the 32 MB texture back: a closed viewer keeps only 1×1.
+      gl.bindTexture(gl.TEXTURE_2D, texture);
+      gl.texImage2D(
+        gl.TEXTURE_2D,
+        0,
+        gl.RGBA,
+        1,
+        1,
+        0,
+        gl.RGBA,
+        gl.UNSIGNED_BYTE,
+        new Uint8Array(4),
+      );
+      scheduleRender();
+    },
+    destroy() {
+      if (frame) cancelAnimationFrame(frame);
+      frame = 0;
+      loaded = false;
+      gl.deleteTexture(texture);
+      gl.deleteBuffer(buffer);
+      gl.deleteProgram(program);
+      gl.getExtension('WEBGL_lose_context')?.loseContext();
+    },
+  };
+}

src/layers/streetLevel/providers/kartaview/panorama.test.mjs

@@ -0,0 +1,169 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import {
+  PANO_FOV_MAX_DEG,
+  PANO_FOV_MIN_DEG,
+  PANO_PITCH_LIMIT_DEG,
+  clampFov,
+  clampPitch,
+  createPanoramaRenderer,
+  rayToUv,
+  wrapDegrees,
+} from './panorama.js';
+
+const close = (actual, expected) =>
+  actual.forEach((value, i) =>
+    assert.ok(Math.abs(value - expected[i]) < 1e-9, `${actual} ≉ ${expected}`),
+  );
+
+test('straight ahead samples the image centre; yaw turns right, pitch looks up', () => {
+  close(rayToUv([0, 0, -1]), [0.5, 0.5]);
+  close(rayToUv([0, 0, -1], { yaw: 90 }), [0.75, 0.5]);
+  close(rayToUv([0, 0, -1], { yaw: -90 }), [0.25, 0.5]);
+  close(rayToUv([0, 0, -1], { pitch: 45 }), [0.5, 0.25]);
+  close(rayToUv([0, 0, -1], { pitch: -90 }), [0.5, 1]);
+  // Pitch first, then yaw: looking up-right stays up.
+  close(rayToUv([0, 0, -1], { yaw: 90, pitch: 45 }), [0.75, 0.25]);
+  // A ray to the right of the screen is the same as turning right.
+  close(rayToUv([1, 0, 0]), [0.75, 0.5]);
+});
+
+test('view limits: pitch stops short of the poles, field of view stays usable', () => {
+  assert.equal(clampPitch(120), PANO_PITCH_LIMIT_DEG);
+  assert.equal(clampPitch(-120), -PANO_PITCH_LIMIT_DEG);
+  assert.equal(clampFov(5), PANO_FOV_MIN_DEG);
+  assert.equal(clampFov(170), PANO_FOV_MAX_DEG);
+  assert.equal(wrapDegrees(-30), 330);
+  assert.equal(wrapDegrees(725), 5);
+});
+
+/**
+ * A WebGL stand-in that records draw calls and uniform values; `lost` makes
+ * it report a lost context.
+ */
+function stubGl() {
+  const gl = {
+    lost: false,
+    calls: [],
+    uniforms: {},
+    isContextLost: () => gl.lost,
+    getShaderParameter: () => true,
+    getProgramParameter: () => true,
+    getUniformLocation: (program, name) => name,
+    getExtension: () => null,
+    uniform1f: (name, value) => (gl.uniforms[name] = value),
+  };
+  return new Proxy(gl, {
+    get(target, key) {
+      if (key in target) return target[key];
+      if (typeof key === 'string' && /^[A-Z_0-9]+$/.test(key)) return key;
+      return (...args) => {
+        target.calls.push(key);
+        return { key, args };
+      };
+    },
+  });
+}
+
+/** A panorama on a stub canvas, with frames run when the test says. */
+function stubPanorama(t, { width = 400, height = 250 } = {}) {
+  const gl = stubGl();
+  const canvas = {
+    clientWidth: width,
+    clientHeight: height,
+    width: 300,
+    height: 150,
+    getContext: () => gl,
+  };
+  const frames = [];
+  const saved = {
+    request: globalThis.requestAnimationFrame,
+    cancel: globalThis.cancelAnimationFrame,
+  };
+  globalThis.requestAnimationFrame = (callback) => frames.push(callback);
+  globalThis.cancelAnimationFrame = () => {};
+  t.after(() => {
+    globalThis.requestAnimationFrame = saved.request;
+    globalThis.cancelAnimationFrame = saved.cancel;
+  });
+  const renderer = createPanoramaRenderer(canvas);
+  const runFrames = () => {
+    while (frames.length) frames.shift()();
+  };
+  return { gl, canvas, renderer, runFrames };
+}
+
+const IMAGE = { width: 1024, height: 512 };
+
+test('a panorama draws once it has an image; looking up and right are positive angles', (t) => {
+  const { gl, renderer, runFrames } = stubPanorama(t);
+  renderer.render();
+  runFrames();
+  assert.equal(gl.calls.includes('drawArrays'), false, 'nothing to draw yet');
+  renderer.setImage(IMAGE);
+  renderer.setView({ yaw: 30, pitch: 30 });
+  runFrames();
+  assert.ok(gl.calls.includes('drawArrays'));
+  assert.ok(gl.uniforms.u_pitch > 0, `u_pitch ${gl.uniforms.u_pitch}`);
+  assert.ok(Math.abs(gl.uniforms.u_pitch - Math.PI / 6) < 1e-9);
+  assert.ok(Math.abs(gl.uniforms.u_yaw - Math.PI / 6) < 1e-9);
+  renderer.setView({ pitch: -20 });
+  runFrames();
+  assert.ok(gl.uniforms.u_pitch < 0, 'looking down is negative');
+});
+
+test('a lost WebGL context draws nothing', (t) => {
+  const { gl, renderer, runFrames } = stubPanorama(t);
+  renderer.setImage(IMAGE);
+  gl.lost = true;
+  gl.calls.length = 0;
+  runFrames();
+  assert.deepEqual(
+    gl.calls.filter((call) =>
+      ['viewport', 'clear', 'drawArrays'].includes(call),
+    ),
+    [],
+  );
+});
+
+test('the canvas is measured again when it draws, not only when its image arrived', (t) => {
+  // The image arrives while the canvas is still hidden (0×0)…
+  const { canvas, renderer, runFrames } = stubPanorama(t, {
+    width: 0,
+    height: 0,
+  });
+  renderer.setImage(IMAGE);
+  assert.deepEqual([canvas.width, canvas.height], [1, 1]);
+  // …and is laid out before the frame draws.
+  canvas.clientWidth = 400;
+  canvas.clientHeight = 250;
+  runFrames();
+  assert.deepEqual([canvas.width, canvas.height], [400, 250]);
+});
+
+test('an image uploads as RGBA and its bitmap is released; closing hands the texture back as 1×1', (t) => {
+  const { gl, renderer } = stubPanorama(t);
+  const uploads = [];
+  gl.texImage2D = (...args) => uploads.push(args);
+  let closed = false;
+  renderer.setImage({
+    width: 2048,
+    height: 1024,
+    close: () => (closed = true),
+  });
+  assert.equal(uploads.length, 1);
+  assert.equal(
+    uploads[0][2],
+    'RGBA',
+    'the format a decoded bitmap uploads without conversion',
+  );
+  assert.equal(closed, true, 'the decoded copy is freed once on the GPU');
+  renderer.clear();
+  const last = uploads.at(-1);
+  assert.deepEqual(
+    [last[3], last[4]],
+    [1, 1],
+    'a closed viewer keeps a 1×1 texture',
+  );
+  assert.equal(renderer.hasImage(), false);
+});

src/layers/streetLevel/providers/kartaview/policy.js

@@ -0,0 +1,397 @@
+import { COLORS as SHARED_COLORS, PROVIDER_COLORS } from '../../policy.js';
+
+export { NEAREST_RADIUS_M } from '../../policy.js';
+
+/** Identity and tuning for the KartaView street-level provider (keyless). */
+export const KARTAVIEW_PROVIDER_ID = 'kartaview';
+export const KARTAVIEW_NAME = 'KartaView';
+export const KARTAVIEW_LABEL = 'KARTAVIEW';
+
+/**
+ * The public API. Its documented twin, api.openstreetcam.org, still answers
+ * but serves empty coverage tiles.
+ */
+export const KARTAVIEW_API_HOST = 'https://api.kartaview.org';
+/** KartaView's image proxy: resizes a photo given its base64url address. */
+export const KARTAVIEW_CDN_HOST = 'https://cdn.kartaview.org';
+
+/** Stable id prefixes for picked primitives; every one starts with `kv:`. */
+export const PICK_PREFIX = Object.freeze({
+  root: 'kv:',
+  line: 'kv:line:',
+  image: 'kv:img:',
+});
+
+export const COLORS = Object.freeze({
+  coverage: PROVIDER_COLORS.kartaview,
+  selected: SHARED_COLORS.selected,
+});
+
+/**
+ * Coverage lines are OSM ways with photos, from z13–14 JSON tiles. Lower
+ * zooms take seconds per tile (z10 does not answer), so higher up the panel
+ * asks the user to zoom in.
+ */
+export const COVERAGE_STREET_ZOOM_BELOW_M = 2_500;
+export const COVERAGE_MAX_HEIGHT_M = 6_000;
+export const COVERAGE_TUNING = Object.freeze({
+  maxTiles: 9,
+  overviewMaxTiles: 0,
+  // Chained ways are short: a dense downtown z13 tile holds ~1,500, so each
+  // tile may draw 1,600 (a frame stays at 16.7 ms with 4,400 drawn).
+  maxSequences: 14_400,
+  lineWidthPx: 2.5,
+  overviewPointPx: 2.5,
+  moveDebounceMs: 320,
+  viewRangeMinM: 2_500,
+  viewRangePerHeight: 10,
+  viewNearM: 1_000,
+});
+export const TOO_HIGH_HINT = 'zoom in to see KartaView coverage';
+export const NO_COVERAGE_HINT = 'no KartaView photos in view';
+export const RATE_LIMITED_MESSAGE =
+  'KartaView is rate-limiting requests — they resume on their own';
+
+/**
+ * The photo API answers 429 to more than about three requests at once, so
+ * at most two are in flight; a 429 is retried after a short wait.
+ */
+export const PHOTO_API_CONCURRENCY = 2;
+export const PHOTO_API_RETRIES = 3;
+export const PHOTO_API_RETRY_BASE_MS = 800;
+/** A Retry-After longer than this is not waited out. */
+export const PHOTO_API_RETRY_MAX_MS = 10_000;
+/** The API is HTTP/1.1 (six connections): tiles 3, lookups 2, pages 1. */
+export const TILE_CONCURRENCY = 3;
+export const PAGE_CONCURRENCY = 1;
+export const TILE_TIMEOUT_MS = 20_000;
+export const PHOTO_API_TIMEOUT_MS = 15_000;
+/**
+ * The first try of a lookup: KartaView sometimes sits on a lookup for 11 s
+ * and more, then answers the same one again in 3 s.
+ */
+export const PHOTO_API_FIRST_TIMEOUT_MS = 8_000;
+/** A sequence page is about 650 kB of JSON. */
+export const PAGE_TIMEOUT_MS = 30_000;
+/** Real tiles are under 1 MB; refuse anything absurd before parsing it. */
+export const MAX_RESPONSE_BYTES = 16 * 1024 * 1024;
+/** A photo download (tens of kilobytes to a few megabytes). */
+export const IMAGE_TIMEOUT_MS = 15_000;
+/** Whether a photo file is there (not archived): headers only. */
+export const IMAGE_PROBE_TIMEOUT_MS = 8_000;
+/** Nearest photos probed (at once) before giving up on archived ones; ‹ › skip this many. */
+export const NEAREST_PROBES = 6;
+export const ARCHIVED_MESSAGE =
+  'KartaView’s photos here are archived and cannot be shown';
+
+/** Photos asked for around a point; the API returns them nearest first. */
+export const NEAREST_LIMIT = 10;
+/** The photo API's search zoom: 18 searches the few tens of metres around the point. */
+export const NEAREST_SEARCH_ZOOM = 18;
+
+/**
+ * Photos of a sequence fetched at once, around the open one. Records are
+ * ~2.6 kB each, so a page is ~650 kB; the cones and ‹ › use it. Pages are in
+ * photo-id order, which only roughly follows the sequence index.
+ */
+export const SEQUENCE_PAGE_SIZE = 250;
+/** Within this many photos of a page's edge, its neighbour page joins it. */
+export const SEQUENCE_PAGE_EDGE = 12;
+
+/** Equirectangular panorama sizes: a quick preview, then the sharp one. */
+export const PANO_PREVIEW_SIZE = Object.freeze([1024, 512]);
+/** Enough for a docked viewer; an expanded one gets the full size. */
+export const PANO_MID_SIZE = Object.freeze([2048, 1024]);
+export const PANO_FULL_SIZE = Object.freeze([4096, 2048]);
+/** A flat photo's first version, then its sharp one. */
+export const FLAT_VIEW_SIZE = Object.freeze([1280, 1280]);
+export const FLAT_FULL_SIZE = Object.freeze([2560, 2560]);
+
+/** On-globe credit: KartaView imagery is CC BY-SA 4.0 and needs attribution. */
+export const KARTAVIEW_CREDIT_HTML =
+  'Street Level: imagery © <a href="https://kartaview.org" target="_blank" rel="noopener">KartaView</a> contributors, CC BY-SA 4.0';
+
+/**
+ * The imagery filter (360° or flat, SINCE). KartaView filters coverage on
+ * its server only in its PNG tiles: its JSON tiles come back empty once a
+ * filter is asked for. So a filtered PNG tile is a mask, and a JSON line is
+ * kept where it lies on the mask's drawn pixels.
+ *
+ * KartaView's date filter is the upload date, and SINCE goes by it
+ * throughout (lines, the photo a click opens, the cones), as KartaView's own
+ * map does; the panel says so under the slider.
+ */
+export const MASK_TIMEOUT_MS = 20_000;
+/**
+ * A filtered PNG tile is drawn on demand and a dense one can outlast
+ * KartaView's own 60 s (504); it keeps drawing, and has the tile a few
+ * seconds later. A timeout or a 5xx is asked again this many times in all.
+ */
+export const MASK_ATTEMPTS = 4;
+export const MASK_RETRY_WAIT_MS = 4_000;
+/** Real masks are tens of kilobytes. */
+export const MASK_MAX_BYTES = 2 * 1024 * 1024;
+/** A segment is kept when this share of the points along it lies on the mask. */
+export const MASK_KEEP_SHARE = 0.5;
+/** Points along a segment are tested this many mask pixels apart. */
+export const MASK_SAMPLE_PX = 2;
+export const MASK_SLOW_MESSAGE =
+  'KartaView did not filter this area in time — move the map to ask again';
+export const FILTERED_OUT_MESSAGE =
+  'None of KartaView’s photos here pass the imagery filter';
+/** Under the SINCE slider while KartaView is lit. */
+export const SINCE_NOTE = 'KartaView: by upload date';
+
+/** The UTC calendar day of `ms`, as KartaView's startDate reads it. */
+function utcDay(ms) {
+  return new Date(ms).toISOString().slice(0, 10);
+}
+
+const filtersSince = (filter) =>
+  Number.isFinite(filter?.sinceMs) && filter.sinceMs > 0;
+
+const DAY_MS = 86_400_000;
+
+/**
+ * Whether a photo passes the resolved imagery filter by its projection and
+ * upload date, the cut-off taken as its UTC day, as KartaView's startDate.
+ * @param {{isPano: boolean, uploadedAt: number|null}} photo
+ * @param {{pano: string, sinceMs: number|null}|null} filter
+ */
+export function passesKartaViewFilter(photo, filter) {
+  if (!filter) return true;
+  if (filter.pano === 'pano' && !photo.isPano) return false;
+  if (filter.pano === 'flat' && photo.isPano) return false;
+  if (!filtersSince(filter)) return true;
+  const day = Math.floor(filter.sinceMs / DAY_MS) * DAY_MS;
+  return (photo.uploadedAt ?? 0) >= day;
+}
+
+/**
+ * The query of a filtered PNG coverage tile, or '' when nothing is
+ * filtered. The day, not the instant, so it is stable for a day (and keys
+ * the mask cache).
+ * @param {{pano: string, sinceMs: number|null}|null} filter  resolved
+ */
+export function tileFilterQuery(filter) {
+  const params = new URLSearchParams();
+  if (filter?.pano === 'pano') params.set('fieldOfView', '360');
+  else if (filter?.pano === 'flat') params.set('fieldOfView', 'plane');
+  if (filtersSince(filter)) params.set('startDate', utcDay(filter.sinceMs));
+  return params.toString();
+}
+
+/**
+ * The photo search's own filter: projection and upload date (its
+ * `fieldOfView` is ignored).
+ * @param {{pano: string, sinceMs: number|null}|null} filter  resolved
+ * @returns {Record<string, string>}
+ */
+export function photoFilterParams(filter) {
+  const params = {};
+  if (filter?.pano === 'pano') params.projection = 'SPHERE';
+  else if (filter?.pano === 'flat') params.projection = 'PLANE';
+  if (filtersSince(filter)) params.startDate = utcDay(filter.sinceMs);
+  return params;
+}
+
+/** The cone and coverage noun: a line is a street with photos, not a sequence. */
+export const COVERAGE_NOUN = 'streets';
+export const LINE_CLICK_HINT = 'click a line for its nearest photo';
+
+/** Base64url of a string, as the image proxy reads addresses. */
+function base64Url(text) {
+  const bytes = new TextEncoder().encode(text);
+  let binary = '';
+  for (const byte of bytes) binary += String.fromCharCode(byte);
+  return btoa(binary)
+    .replace(/\+/g, '-')
+    .replace(/\//g, '_')
+    .replace(/=+$/, '');
+}
+
+/** A photo resized by KartaView's image proxy to fit `width`×`height`. */
+export function resizedImageUrl(url, [width, height]) {
+  if (!url) return null;
+  return `${KARTAVIEW_CDN_HOST}/pr:sharp/rs:fit:${width}:${height}/${base64Url(url)}`;
+}
+
+/** Epoch ms for a KartaView timestamp ('2016-02-19 15:28:18.000', UTC), or null. */
+export function kartaViewTimeMs(value) {
+  const match =
+    /^(\d{4})-(\d{2})-(\d{2})(?:[ T](\d{2}):(\d{2})(?::(\d{2}))?)?/.exec(
+      String(value ?? ''),
+    );
+  if (!match) return null;
+  const [, y, mo, d, h = '0', mi = '0', s = '0'] = match;
+  if (Number(y) < 1990) return null;
+  const ms = Date.UTC(+y, +mo - 1, +d, +h, +mi, +s);
+  return Number.isFinite(ms) ? ms : null;
+}
+
+/** Initial great-circle bearing from `a` to `b`, degrees clockwise from north. */
+export function bearingBetween(a, b) {
+  const rad = Math.PI / 180;
+  const dLon = (b.lon - a.lon) * rad;
+  const y = Math.sin(dLon) * Math.cos(b.lat * rad);
+  const x =
+    Math.cos(a.lat * rad) * Math.sin(b.lat * rad) -
+    Math.sin(a.lat * rad) * Math.cos(b.lat * rad) * Math.cos(dLon);
+  return (Math.atan2(y, x) / rad + 360) % 360;
+}
+
+/** Photos closer than this say nothing about the direction of travel. */
+const COURSE_MIN_STEP_M = 2;
+/** How many photos along to look for one far enough away. */
+const COURSE_SEARCH = 5;
+
+/**
+ * Give each photo of a drive (in index order) its `course`: the direction
+ * of travel from it to the next photo a few metres on (from the previous one
+ * at the end). KartaView is dashcam imagery, so this is where the camera
+ * looks; its `heading` is the device compass, which reads 0 without one and
+ * can sit 110° off inside a car.
+ * @param {Array<{lon: number, lat: number, course?: number|null}>} photos
+ * @param {(a: object, b: object) => number} metres
+ */
+export function assignCourses(photos, metres) {
+  photos.forEach((photo, i) => {
+    let course = null;
+    for (let j = i + 1; j <= i + COURSE_SEARCH && j < photos.length; j++)
+      if (metres(photo, photos[j]) >= COURSE_MIN_STEP_M) {
+        course = bearingBetween(photo, photos[j]);
+        break;
+      }
+    for (
+      let k = i - 1;
+      course === null && k >= i - COURSE_SEARCH && k >= 0;
+      k--
+    )
+      if (metres(photos[k], photo) >= COURSE_MIN_STEP_M)
+        course = bearingBetween(photos[k], photo);
+    photo.course = course;
+  });
+  return photos;
+}
+
+/** Where the camera looked: the direction of travel, else the compass, else unknown. */
+export function cameraBearing(photo) {
+  return photo?.course ?? photo?.heading ?? null;
+}
+
+/** A coordinate pair as numbers; the road-matched one when KartaView has it. */
+function positionOf(record) {
+  const matchLat = Number(record.matchLat);
+  const matchLon = Number(record.matchLng);
+  if (
+    Number.isFinite(matchLat) &&
+    Number.isFinite(matchLon) &&
+    (matchLat !== 0 || matchLon !== 0)
+  )
+    return { lat: matchLat, lon: matchLon };
+  return { lat: Number(record.lat), lon: Number(record.lng) };
+}
+
+const STORAGE_HOST = /^storage\d+$/;
+
+/** A KartaView photo-storage address, or null for anything else. */
+function storageUrl(value) {
+  try {
+    const url = new URL(String(value));
+    return url.protocol === 'https:' &&
+      /^storage\d+\.openstreetcam\.org$/.test(url.hostname)
+      ? url.href
+      : null;
+  } catch {
+    return null;
+  }
+}
+
+/**
+ * A photo file's address. The API's `fileurl*` fields always name storage1,
+ * but a photo whose `storage` is another host (storage2…) is only there, so
+ * the address is built from `storage` and the relative `filepath*`. A
+ * `fileurl*` fallback must itself be on KartaView's storage.
+ */
+function fileUrl(record, pathKey, urlKey) {
+  const path = record[pathKey];
+  if (STORAGE_HOST.test(record.storage || '') && path)
+    return storageUrl(
+      `https://${record.storage}.openstreetcam.org/files/photo/${path}`,
+    );
+  return storageUrl(record[urlKey]);
+}
+
+/** A storage URL with its `{{sizeprefix}}` placeholder filled. */
+function sized(record, prefix) {
+  const fill = (value) =>
+    typeof value === 'string' && value.includes('{{sizeprefix}}')
+      ? value.replace('{{sizeprefix}}', prefix)
+      : null;
+  const path = fill(record.filepath);
+  return fileUrl(
+    { ...record, filepath: path, fileurl: fill(record.fileurl) },
+    'filepath',
+    'fileurl',
+  );
+}
+
+/**
+ * A photo API record in the shape the provider uses, or null without an id
+ * or a position.
+ * @returns {{id: string, sequenceId: string|null, sequenceIndex: number|null, lon: number, lat: number, heading: number|null, isPano: boolean, capturedAt: number|null, urls: {view: string|null, full: string|null, pano: string|null}}|null}
+ */
+export function normalizePhoto(record) {
+  if (!record || record.id == null) return null;
+  const { lat, lon } = positionOf(record);
+  if (!Number.isFinite(lat) || !Number.isFinite(lon)) return null;
+  // 0,0 is a missing fix, not a photo in the Gulf of Guinea.
+  if (lat === 0 && lon === 0) return null;
+  if (Math.abs(lat) > 90 || Math.abs(lon) > 180) return null;
+  // An exact 0 is a device without a compass (whole drives read 0), not north.
+  const heading =
+    record.heading === '' || record.heading == null
+      ? NaN
+      : Number(record.heading) || NaN;
+  const isPano =
+    record.projection === 'SPHERE' || Number(record.fieldOfView) >= 360;
+  const full =
+    fileUrl(record, 'filepathProc', 'fileurlProc') || sized(record, 'proc');
+  const index = Number(record.sequenceIndex);
+  return {
+    id: String(record.id),
+    sequenceId: record.sequenceId != null ? String(record.sequenceId) : null,
+    sequenceIndex: Number.isFinite(index) ? index : null,
+    lon,
+    lat,
+    heading: Number.isFinite(heading) ? heading : null,
+    isPano,
+    capturedAt:
+      kartaViewTimeMs(record.shotDate) ?? kartaViewTimeMs(record.dateAdded),
+    // KartaView's SINCE goes by this (its server filters by upload date).
+    uploadedAt: kartaViewTimeMs(record.dateAdded),
+    urls: {
+      // A 1280 px rendition; for a 360° photo it is the front view only.
+      view:
+        fileUrl(record, 'filepathLTh', 'fileurlLTh') ||
+        sized(record, 'lth') ||
+        full,
+      full,
+      // A 360° photo's equirectangular image ('wrapped_proc').
+      pano: isPano && /wrapped/.test(full || '') ? full : null,
+    },
+  };
+}
+
+/**
+ * Where the image link goes. KartaView's photo pages fail for signed-out
+ * visitors ("Sequence cannot be loaded"), so it is the full-size photo
+ * through KartaView's image proxy, which also serves photos whose storage
+ * host answers 502 directly.
+ */
+export function kartaViewPhotoUrl(photo) {
+  const url = photo?.urls?.full || photo?.urls?.view;
+  return url
+    ? `${KARTAVIEW_CDN_HOST}/pr:sharp/${base64Url(url)}`
+    : 'https://kartaview.org';
+}

src/layers/streetLevel/providers/kartaview/policy.test.mjs

@@ -0,0 +1,348 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import {
+  assignCourses,
+  bearingBetween,
+  cameraBearing,
+  kartaViewPhotoUrl,
+  kartaViewTimeMs,
+  normalizePhoto,
+  passesKartaViewFilter,
+  photoFilterParams,
+  resizedImageUrl,
+  tileFilterQuery,
+} from './policy.js';
+
+/** A photo record as /2.0/photo returns it (trimmed to what is read). */
+function record(overrides = {}) {
+  return {
+    id: '7102491',
+    sequenceId: '14010',
+    sequenceIndex: '950',
+    lat: '42.335712',
+    lng: '-83.048301',
+    matchLat: '42.335731506347656',
+    matchLng: '-83.04828643798828',
+    heading: '299.58',
+    fieldOfView: '0',
+    projection: 'PLANE',
+    shotDate: '2016-08-23 20:17:47.000',
+    dateAdded: '2016-08-24 04:01:07',
+    storage: 'storage1',
+    filepath: '2016/8/24/{{sizeprefix}}/14010_ba53c_57bd1d23d50b7.jpg',
+    filepathLTh: '2016/8/24/lth/14010_ba53c_57bd1d23d50b7.jpg',
+    filepathProc: '2016/8/24/proc/14010_ba53c_57bd1d23d50b7.jpg',
+    fileurl:
+      'https://storage1.openstreetcam.org/files/photo/2016/8/24/{{sizeprefix}}/14010_ba53c_57bd1d23d50b7.jpg',
+    fileurlLTh:
+      'https://storage1.openstreetcam.org/files/photo/2016/8/24/lth/14010_ba53c_57bd1d23d50b7.jpg',
+    fileurlProc:
+      'https://storage1.openstreetcam.org/files/photo/2016/8/24/proc/14010_ba53c_57bd1d23d50b7.jpg',
+    ...overrides,
+  };
+}
+
+test('a photo record normalizes to numbers, the road-matched position and UTC capture time', () => {
+  const photo = normalizePhoto(record());
+  assert.equal(photo.id, '7102491');
+  assert.equal(photo.sequenceId, '14010');
+  assert.equal(photo.sequenceIndex, 950);
+  assert.equal(photo.lat, 42.335731506347656);
+  assert.equal(photo.lon, -83.04828643798828);
+  assert.equal(photo.heading, 299.58);
+  assert.equal(photo.isPano, false);
+  assert.equal(photo.capturedAt, Date.UTC(2016, 7, 23, 20, 17, 47));
+  assert.equal(photo.urls.pano, null);
+});
+
+test('photo files come from the storage host the record names, not the one its URLs say', () => {
+  // The API writes storage1 into every URL; this photo lives on storage2.
+  const photo = normalizePhoto(record({ storage: 'storage2' }));
+  assert.equal(
+    photo.urls.view,
+    'https://storage2.openstreetcam.org/files/photo/2016/8/24/lth/14010_ba53c_57bd1d23d50b7.jpg',
+  );
+  assert.equal(
+    photo.urls.full,
+    'https://storage2.openstreetcam.org/files/photo/2016/8/24/proc/14010_ba53c_57bd1d23d50b7.jpg',
+  );
+  // The link goes through the image proxy, which serves photos whose
+  // storage host answers 502 directly.
+  const link = kartaViewPhotoUrl(photo);
+  assert.match(link, /^https:\/\/cdn\.kartaview\.org\/pr:sharp\/[\w-]+$/);
+  assert.equal(
+    Buffer.from(link.split('/').at(-1), 'base64url').toString(),
+    photo.urls.full,
+  );
+  // A fallback address must be on KartaView's storage, over https.
+  for (const fileurlLTh of [
+    'https://tracker.example/x.jpg',
+    'http://storage1.openstreetcam.org/a.jpg',
+    'https://storage1.openstreetcam.org.evil.example/a.jpg',
+    'javascript:alert(1)',
+  ]) {
+    const hostile = normalizePhoto(
+      record({ storage: '', filepathLTh: '', fileurlLTh, fileurl: fileurlLTh }),
+    );
+    assert.notEqual(hostile.urls.view, fileurlLTh);
+    assert.doesNotMatch(
+      String(hostile.urls.view),
+      /tracker|javascript|evil|^http:/,
+    );
+  }
+  // An unexpected storage value falls back to the URLs as given.
+  const odd = normalizePhoto(record({ storage: 'https://evil.example' }));
+  assert.match(odd.urls.view, /^https:\/\/storage1\.openstreetcam\.org\//);
+  // No large thumbnail path: the size prefix fills in.
+  const bare = normalizePhoto(
+    record({ filepathLTh: '', fileurlLTh: '', storage: 'storage3' }),
+  );
+  assert.equal(
+    bare.urls.view,
+    'https://storage3.openstreetcam.org/files/photo/2016/8/24/lth/14010_ba53c_57bd1d23d50b7.jpg',
+  );
+});
+
+test('a 360° photo keeps its equirectangular image; the unmatched position is the fallback', () => {
+  const photo = normalizePhoto(
+    record({
+      projection: 'SPHERE',
+      fieldOfView: '360',
+      matchLat: '0',
+      matchLng: '0',
+      storage: 'storage13',
+      filepathProc: '2022/10/6/wrapped_proc/6187609_626b8.jpg',
+    }),
+  );
+  assert.equal(photo.isPano, true);
+  assert.equal(photo.lat, 42.335712);
+  assert.equal(
+    photo.urls.pano,
+    'https://storage13.openstreetcam.org/files/photo/2022/10/6/wrapped_proc/6187609_626b8.jpg',
+  );
+  // A sphere without a wrapped image has nothing to project.
+  assert.equal(
+    normalizePhoto(record({ projection: 'SPHERE', fieldOfView: '360' })).urls
+      .pano,
+    null,
+  );
+});
+
+test('records without an id or a position are dropped; a missing heading is null', () => {
+  assert.equal(normalizePhoto(null), null);
+  // 0,0 is a missing fix.
+  assert.equal(
+    normalizePhoto(
+      record({ lat: '0', lng: '0', matchLat: '0', matchLng: '0' }),
+    ),
+    null,
+  );
+  assert.equal(normalizePhoto(record({ lat: '95', matchLat: '95' })), null);
+  assert.equal(normalizePhoto(record({ id: undefined })), null);
+  assert.equal(
+    normalizePhoto(
+      record({ lat: 'x', lng: 'y', matchLat: undefined, matchLng: undefined }),
+    ),
+    null,
+  );
+  assert.equal(normalizePhoto(record({ heading: '' })).heading, null);
+  // A device without a compass reads 0 for a whole drive: unknown, not north.
+  assert.equal(normalizePhoto(record({ heading: '0' })).heading, null);
+  assert.equal(normalizePhoto(record({ heading: '0.5' })).heading, 0.5);
+  assert.equal(normalizePhoto(record({ heading: 'n/a' })).heading, null);
+});
+
+test('timestamps parse as UTC; years before 1990 and garbage are unknown', () => {
+  assert.equal(kartaViewTimeMs('2022-03-21'), Date.UTC(2022, 2, 21));
+  assert.equal(
+    kartaViewTimeMs('2022-03-21T06:42:59'),
+    Date.UTC(2022, 2, 21, 6, 42, 59),
+  );
+  assert.equal(kartaViewTimeMs('0000-00-00 00:00:00'), null);
+  assert.equal(kartaViewTimeMs(''), null);
+  assert.equal(kartaViewTimeMs(null), null);
+  const fallback = normalizePhoto(record({ shotDate: null }));
+  assert.equal(fallback.capturedAt, Date.UTC(2016, 7, 24, 4, 1, 7));
+});
+
+test('resized images go through the proxy with a base64url address', () => {
+  const url = resizedImageUrl(
+    'https://storage13.openstreetcam.org/files/photo/a?b=c+d',
+    [1024, 512],
+  );
+  const [, encoded] = /\/rs:fit:1024:512\/(.+)$/.exec(url);
+  assert.match(url, /^https:\/\/cdn\.kartaview\.org\/pr:sharp\/rs:fit:/);
+  assert.doesNotMatch(encoded, /[+/=]/);
+  const decoded = Buffer.from(
+    encoded.replace(/-/g, '+').replace(/_/g, '/'),
+    'base64',
+  ).toString();
+  assert.equal(
+    decoded,
+    'https://storage13.openstreetcam.org/files/photo/a?b=c+d',
+  );
+  assert.equal(resizedImageUrl(null, [1, 1]), null);
+});
+
+test('a storage value that only contains a storage host name builds no address from it', () => {
+  for (const storage of ['evil.example/#storage1', 'storage1.evil.example']) {
+    const photo = normalizePhoto(record({ storage }));
+    // Not a storage host: the API's own storage URLs serve.
+    assert.equal(
+      photo.urls.view,
+      'https://storage1.openstreetcam.org/files/photo/2016/8/24/lth/14010_ba53c_57bd1d23d50b7.jpg',
+      storage,
+    );
+    assert.equal(
+      photo.urls.full,
+      'https://storage1.openstreetcam.org/files/photo/2016/8/24/proc/14010_ba53c_57bd1d23d50b7.jpg',
+      storage,
+    );
+  }
+});
+
+test('a 360° field of view makes a panorama whatever the projection says', () => {
+  assert.equal(
+    normalizePhoto(record({ projection: 'PLANE', fieldOfView: '360' })).isPano,
+    true,
+  );
+  assert.equal(
+    normalizePhoto(record({ projection: 'PLANE', fieldOfView: '359' })).isPano,
+    false,
+  );
+});
+
+test('a longitude past ±180 is not a position', () => {
+  assert.equal(normalizePhoto(record({ lng: '181', matchLng: '181' })), null);
+  assert.equal(normalizePhoto(record({ lng: '-181', matchLng: '-181' })), null);
+  assert.equal(
+    normalizePhoto(record({ lng: '180', matchLng: '180' })).lon,
+    180,
+  );
+});
+
+test('with no processed-photo path the size prefix gives the full photo', () => {
+  const photo = normalizePhoto(
+    record({ filepathProc: '', fileurlProc: '', storage: 'storage3' }),
+  );
+  assert.equal(
+    photo.urls.full,
+    'https://storage3.openstreetcam.org/files/photo/2016/8/24/proc/14010_ba53c_57bd1d23d50b7.jpg',
+  );
+  // Only the large thumbnail, no path at all: the thumbnail still shows.
+  const thumbOnly = normalizePhoto(
+    record({
+      filepathProc: '',
+      fileurlProc: '',
+      filepath: '',
+      fileurl: '',
+      storage: 'storage3',
+    }),
+  );
+  assert.equal(thumbOnly.urls.full, null);
+  assert.match(
+    thumbOnly.urls.view,
+    /^https:\/\/storage3\.openstreetcam\.org\/.*\/lth\//,
+  );
+});
+
+test('the camera looks along the drive: each photo’s course points to the next one a few metres on', () => {
+  // North along a meridian, 5 m apart, then a repeat of the last position.
+  const step = 5 / 110_540;
+  const photos = [0, 1, 2, 3].map((i) => ({ lon: 10, lat: 50 + i * step }));
+  photos.push({ lon: 10, lat: 50 + 3 * step }); // a stop: same place
+  const metres = (a, b) =>
+    Math.hypot(
+      (b.lon - a.lon) * 111_320 * Math.cos((a.lat * Math.PI) / 180),
+      (b.lat - a.lat) * 110_540,
+    );
+  assignCourses(photos, metres);
+  for (const photo of photos)
+    assert.ok(
+      Math.abs(photo.course) < 0.5 || Math.abs(photo.course - 360) < 0.5,
+      `${photo.course}`,
+    );
+  // Eastward: 90°.
+  const east = [0, 1].map((i) => ({ lon: 10 + (i * 5) / 71_600, lat: 50 }));
+  assignCourses(east, metres);
+  assert.ok(
+    Math.abs(east[0].course - 90) < 0.5 && Math.abs(east[1].course - 90) < 0.5,
+  );
+  // A lone photo has no course; the compass is the fallback, then unknown.
+  const [lone] = assignCourses([{ lon: 1, lat: 1 }], metres);
+  assert.equal(lone.course, null);
+  assert.equal(cameraBearing({ ...lone, heading: 42 }), 42);
+  assert.equal(cameraBearing({ ...lone, heading: null }), null);
+  assert.equal(
+    cameraBearing({ course: 90, heading: 200 }),
+    90,
+    'the drive beats the compass',
+  );
+  assert.ok(
+    Math.abs(bearingBetween({ lon: 0, lat: 0 }, { lon: 0, lat: -1 }) - 180) <
+      1e-9,
+  );
+});
+
+test('the imagery filter becomes KartaView’s tile query and photo-search params', () => {
+  // 2026-03-05 23:30 UTC: the cut-off day is the UTC one.
+  const sinceMs = Date.UTC(2026, 2, 5, 23, 30);
+  assert.equal(tileFilterQuery(null), '');
+  assert.equal(tileFilterQuery({ pano: 'all', sinceMs: null }), '');
+  assert.equal(
+    tileFilterQuery({ pano: 'pano', sinceMs: null }),
+    'fieldOfView=360',
+  );
+  assert.equal(
+    tileFilterQuery({ pano: 'flat', sinceMs }),
+    'fieldOfView=plane&startDate=2026-03-05',
+  );
+  assert.equal(tileFilterQuery({ pano: 'all', sinceMs: 0 }), '');
+  // The search ignores fieldOfView; its projection filters instead.
+  assert.deepEqual(photoFilterParams({ pano: 'all', sinceMs: null }), {});
+  assert.deepEqual(photoFilterParams({ pano: 'pano', sinceMs }), {
+    projection: 'SPHERE',
+    startDate: '2026-03-05',
+  });
+  assert.deepEqual(photoFilterParams({ pano: 'flat', sinceMs: null }), {
+    projection: 'PLANE',
+  });
+});
+
+test('KartaView’s SINCE is the upload date, from the start of the cut-off’s UTC day', () => {
+  const photo = normalizePhoto(
+    record({
+      shotDate: '2016-08-23 20:17:47.000',
+      dateAdded: '2026-03-05 00:10:00',
+    }),
+  );
+  assert.equal(photo.uploadedAt, Date.UTC(2026, 2, 5, 0, 10));
+  const since = (iso) => ({ pano: 'all', sinceMs: Date.parse(iso) });
+  // Taken in 2016, uploaded on the cut-off day: it passes, as KartaView's
+  // startDate=2026-03-05 keeps it.
+  assert.equal(
+    passesKartaViewFilter(photo, since('2026-03-05T23:00:00Z')),
+    true,
+  );
+  assert.equal(
+    passesKartaViewFilter(photo, since('2026-03-06T00:00:00Z')),
+    false,
+  );
+  assert.equal(
+    passesKartaViewFilter(photo, { pano: 'pano', sinceMs: null }),
+    false,
+  );
+  assert.equal(
+    passesKartaViewFilter(photo, { pano: 'flat', sinceMs: null }),
+    true,
+  );
+  assert.equal(passesKartaViewFilter(photo, null), true);
+  assert.equal(
+    passesKartaViewFilter(
+      { ...photo, uploadedAt: null },
+      since('2020-01-01T00:00:00Z'),
+    ),
+    false,
+    'no upload date passes no SINCE',
+  );
+});

src/layers/streetLevel/providers/kartaview/source.js

@@ -0,0 +1,459 @@
+import {
+  IMAGE_PROBE_TIMEOUT_MS,
+  MAX_RESPONSE_BYTES,
+  KARTAVIEW_API_HOST,
+  MASK_ATTEMPTS,
+  MASK_MAX_BYTES,
+  MASK_RETRY_WAIT_MS,
+  MASK_SLOW_MESSAGE,
+  MASK_TIMEOUT_MS,
+  NEAREST_LIMIT,
+  NEAREST_SEARCH_ZOOM,
+  PAGE_CONCURRENCY,
+  PAGE_TIMEOUT_MS,
+  PHOTO_API_CONCURRENCY,
+  PHOTO_API_RETRIES,
+  PHOTO_API_RETRY_BASE_MS,
+  PHOTO_API_RETRY_MAX_MS,
+  PHOTO_API_FIRST_TIMEOUT_MS,
+  PHOTO_API_TIMEOUT_MS,
+  TILE_CONCURRENCY,
+  TILE_TIMEOUT_MS,
+  photoFilterParams,
+} from './policy.js';
+
+/**
+ * An HTTP or API failure; `retryAfterSec` is set while KartaView rate-limits,
+ * `timedOut` when it did not answer in time (the one failure worth asking
+ * again at once).
+ */
+export class KartaViewSourceError extends Error {
+  constructor(
+    message,
+    { status = 0, retryAfterSec = null, timedOut = false } = {},
+  ) {
+    super(message);
+    this.name = 'KartaViewSourceError';
+    this.status = status;
+    this.retryAfterSec = retryAfterSec;
+    this.timedOut = timedOut;
+  }
+}
+
+const NO_ANSWER = 'KartaView did not answer in time — try again';
+const UNREACHABLE = 'KartaView could not be reached — check the network';
+const UNREADABLE = 'KartaView sent an answer that could not be read';
+/** Statuses that mean a photo file is gone, not that storage hiccupped. */
+const GONE_STATUSES = Object.freeze([403, 404, 409, 410]);
+
+/** Resolves after `ms`, or rejects when `signal` aborts first. */
+function wait(ms, signal) {
+  return new Promise((resolve, reject) => {
+    if (signal?.aborted) return reject(signal.reason);
+    const timer = setTimeout(done, ms);
+    const onAbort = () => {
+      clearTimeout(timer);
+      reject(signal.reason);
+    };
+    signal?.addEventListener('abort', onAbort, { once: true });
+    function done() {
+      signal?.removeEventListener('abort', onAbort);
+      resolve();
+    }
+  });
+}
+
+/** Seconds from a Retry-After header, or null. */
+function retryAfterSeconds(response) {
+  const header = response.headers?.get?.('retry-after');
+  const value = header == null || header === '' ? NaN : Number(header);
+  return Number.isFinite(value) && value >= 0 ? value : null;
+}
+
+/**
+ * A gate letting at most `limit` tasks run at once, first in first out, or
+ * newest first with `lifo` (the last request is the one the user waits on).
+ */
+export function createLimiter(limit, { lifo = false } = {}) {
+  let running = 0;
+  const queue = [];
+  function next() {
+    while (running < limit && queue.length) {
+      const { task, resolve, reject, signal } = lifo
+        ? queue.pop()
+        : queue.shift();
+      if (signal?.aborted) {
+        reject(signal.reason);
+        continue;
+      }
+      running++;
+      Promise.resolve()
+        .then(task)
+        .then(resolve, reject)
+        .finally(() => {
+          running--;
+          next();
+        });
+    }
+  }
+  return {
+    run(task, { signal } = {}) {
+      return new Promise((resolve, reject) => {
+        const item = { task, resolve, reject, signal };
+        queue.push(item);
+        signal?.addEventListener(
+          'abort',
+          () => {
+            const at = queue.indexOf(item);
+            if (at === -1) return;
+            queue.splice(at, 1);
+            reject(signal.reason);
+          },
+          { once: true },
+        );
+        next();
+      });
+    },
+    get pending() {
+      return running + queue.length;
+    },
+  };
+}
+
+/**
+ * KartaView's public API, browser-side and keyless (it allows any origin).
+ * It speaks HTTP/1.1, so the browser opens six connections to it: tiles take
+ * at most three, photo lookups two and sequence pages one, so a lookup never
+ * waits behind slow tiles or pages. The photo API answers 429 to more than
+ * about three requests at once; a 429 (and a lookup that timed out) is
+ * retried.
+ * @param {{fetchImpl?: typeof fetch, apiHost?: string, retryBaseMs?: number, maskRetryMs?: number}} [options]
+ */
+export function createKartaViewSource({
+  fetchImpl = (...args) => globalThis.fetch(...args),
+  apiHost = KARTAVIEW_API_HOST,
+  retryBaseMs = PHOTO_API_RETRY_BASE_MS,
+  maskRetryMs = MASK_RETRY_WAIT_MS,
+} = {}) {
+  const limiter = createLimiter(PHOTO_API_CONCURRENCY);
+  const tileLimiter = createLimiter(TILE_CONCURRENCY);
+  const pageLimiter = createLimiter(PAGE_CONCURRENCY, { lifo: true });
+
+  /** GET JSON within `timeoutMs`; the caller's abort wins over the timeout. */
+  function getJson(url, { signal, timeoutMs }) {
+    return fetchBody(url, { signal, timeoutMs, as: 'json' });
+  }
+
+  /**
+   * GET a body within `timeoutMs`, at most `maxBytes` of it, as parsed JSON
+   * or (`as: 'bytes'`) a Uint8Array; the caller's abort wins over the
+   * timeout.
+   */
+  async function fetchBody(
+    url,
+    { signal, timeoutMs, as = 'json', maxBytes = MAX_RESPONSE_BYTES },
+  ) {
+    const controller = new AbortController();
+    const onAbort = () => controller.abort(signal.reason);
+    if (signal?.aborted) throw signal.reason;
+    signal?.addEventListener('abort', onAbort, { once: true });
+    const timer = setTimeout(
+      () =>
+        controller.abort(
+          new KartaViewSourceError(NO_ANSWER, { timedOut: true }),
+        ),
+      timeoutMs,
+    );
+    let response = null;
+    let read = false;
+    try {
+      response = await fetchImpl(url, { signal: controller.signal });
+      if (response.status === 429)
+        throw new KartaViewSourceError('KartaView is rate-limiting requests', {
+          status: 429,
+          retryAfterSec: retryAfterSeconds(response) ?? 2,
+        });
+      if (!response.ok)
+        throw new KartaViewSourceError(
+          `KartaView answered HTTP ${response.status}`,
+          { status: response.status },
+        );
+      const length = Number(response.headers?.get?.('content-length'));
+      const tooMuch = () =>
+        new KartaViewSourceError('KartaView sent too much data', {
+          status: response.status,
+        });
+      if (length > maxBytes) throw tooMuch();
+      // KartaView answers chunked, without a length: count while reading.
+      const reader = response.body?.getReader?.();
+      if (!reader) {
+        read = true;
+        try {
+          if (as === 'bytes')
+            return new Uint8Array(await response.arrayBuffer());
+          return await response.json();
+        } catch (error) {
+          if (controller.signal.aborted) throw error;
+          throw new KartaViewSourceError(UNREADABLE, {
+            status: response.status,
+          });
+        }
+      }
+      read = true;
+      const chunks = [];
+      let bytes = 0;
+      for (;;) {
+        const { done, value } = await reader.read();
+        if (done) break;
+        bytes += value.byteLength;
+        if (bytes > maxBytes) {
+          reader.cancel().catch(() => {});
+          throw tooMuch();
+        }
+        chunks.push(value);
+      }
+      const body = new Uint8Array(bytes);
+      let offset = 0;
+      for (const chunk of chunks) {
+        body.set(chunk, offset);
+        offset += chunk.byteLength;
+      }
+      if (as === 'bytes') return body;
+      try {
+        return JSON.parse(new TextDecoder().decode(body));
+      } catch {
+        throw new KartaViewSourceError(UNREADABLE, {
+          status: response.status,
+        });
+      }
+    } catch (error) {
+      if (signal?.aborted) throw signal.reason;
+      if (controller.signal.aborted) throw controller.signal.reason;
+      if (error instanceof KartaViewSourceError) throw error;
+      // fetch rejects on no network, a blocked request or a refused CORS check.
+      throw new KartaViewSourceError(UNREACHABLE);
+    } finally {
+      clearTimeout(timer);
+      signal?.removeEventListener('abort', onAbort);
+      // An answer turned away unread (429, an error, too long) still holds
+      // its connection, one of the six the browser has: let it go.
+      if (response && !read) {
+        controller.abort();
+        if (response.body && !response.body.locked)
+          response.body.cancel?.().catch?.(() => {});
+      }
+    }
+  }
+
+  /**
+   * A photo-API call through `gate`, retrying 429s with backoff and, once, a
+   * call that timed out.
+   */
+  async function photoApi(
+    path,
+    params,
+    { signal } = {},
+    {
+      gate = limiter,
+      timeoutMs = PHOTO_API_TIMEOUT_MS,
+      firstTimeoutMs = PHOTO_API_FIRST_TIMEOUT_MS,
+    } = {},
+  ) {
+    const query = params ? `?${new URLSearchParams(params)}` : '';
+    const url = `${apiHost}${path}${query}`;
+    let timeouts = 0;
+    for (let attempt = 0; ; attempt++) {
+      try {
+        const payload = await gate.run(
+          // A slow first answer is usually quick when asked again.
+          () =>
+            getJson(url, {
+              signal,
+              timeoutMs: timeouts === 0 ? firstTimeoutMs : timeoutMs,
+            }),
+          { signal },
+        );
+        const code = Number(payload?.status?.apiCode);
+        // 600 ok, 601 empty, 602 partial: anything else is a refusal.
+        if (Number.isFinite(code) && (code < 600 || code > 603))
+          throw new KartaViewSourceError(
+            `KartaView refused the request (code ${code})`,
+            { status: Number(payload?.status?.httpCode) || 0 },
+          );
+        return payload?.result ?? {};
+      } catch (error) {
+        if (signal?.aborted) throw error;
+        const timedOut = error?.timedOut === true;
+        if (timedOut && timeouts++ < 1) continue;
+        if (error?.status !== 429 || attempt >= PHOTO_API_RETRIES) {
+          if (error?.status === 429)
+            throw new KartaViewSourceError(
+              'KartaView is rate-limiting requests — try again in a moment',
+              { status: 429, retryAfterSec: error.retryAfterSec },
+            );
+          throw error;
+        }
+        await wait(
+          Math.min(
+            PHOTO_API_RETRY_MAX_MS,
+            Math.max(
+              retryBaseMs * 2 ** attempt,
+              (error.retryAfterSec ?? 0) * 1000,
+            ),
+          ),
+          signal,
+        );
+      }
+    }
+  }
+
+  return {
+    /** A coverage tile: `{lines: [{track: [{lat, lng}]}]}`. */
+    async getTile({ x, y, z }, { signal } = {}) {
+      const url = `${apiHost}/2.0/sequence/tiles/${x}/${y}/${z}.json`;
+      const once = () =>
+        tileLimiter.run(
+          () => getJson(url, { signal, timeoutMs: TILE_TIMEOUT_MS }),
+          { signal },
+        );
+      try {
+        return await once();
+      } catch (error) {
+        // A cold dense tile can outlast the timeout; KartaView has it ready
+        // by the second ask.
+        if (signal?.aborted || error?.timedOut !== true) throw error;
+        return once();
+      }
+    },
+
+    /**
+     * A filtered coverage tile as PNG bytes, `query` from tileFilterQuery
+     * (KartaView filters only its PNG tiles). It draws a filtered tile on
+     * demand; a dense one can outlast its own 60 s (504) and still be drawn,
+     * so a timeout or a 5xx is asked again a few seconds later.
+     */
+    async getTileMask({ x, y, z }, query, { signal } = {}) {
+      const url = `${apiHost}/2.0/sequence/tiles/${x}/${y}/${z}.png?${query}`;
+      for (let attempt = 1; ; attempt++) {
+        try {
+          // Outside the gate between tries: a wait holds no connection.
+          return await tileLimiter.run(
+            () =>
+              fetchBody(url, {
+                signal,
+                timeoutMs: MASK_TIMEOUT_MS,
+                as: 'bytes',
+                maxBytes: MASK_MAX_BYTES,
+              }),
+            { signal },
+          );
+        } catch (error) {
+          if (signal?.aborted) throw error;
+          const drawing =
+            error?.timedOut === true || [502, 503, 504].includes(error?.status);
+          if (!drawing) throw error;
+          if (attempt >= MASK_ATTEMPTS)
+            throw new KartaViewSourceError(MASK_SLOW_MESSAGE, {
+              timedOut: true,
+            });
+          await wait(maskRetryMs, signal);
+        }
+      }
+    },
+
+    /**
+     * Whether a photo file is there: true, false when it is gone (archived
+     * photos answer 409, and a HEAD says 200 regardless), or null when the
+     * storage did not say (timeout, network, 5xx). It GETs and stops at the
+     * headers.
+     */
+    async probeImage(url, { signal } = {}) {
+      if (!url) return false;
+      const controller = new AbortController();
+      const onAbort = () => controller.abort(signal.reason);
+      if (signal?.aborted) throw signal.reason;
+      signal?.addEventListener('abort', onAbort, { once: true });
+      const timer = setTimeout(
+        () => controller.abort(),
+        IMAGE_PROBE_TIMEOUT_MS,
+      );
+      try {
+        const response = await fetchImpl(url, { signal: controller.signal });
+        if (response.ok) return true;
+        return GONE_STATUSES.includes(response.status) ? false : null;
+      } catch {
+        if (signal?.aborted) throw signal.reason;
+        return null;
+      } finally {
+        clearTimeout(timer);
+        signal?.removeEventListener('abort', onAbort);
+        // The body is not needed: drop it.
+        controller.abort();
+      }
+    },
+
+    /**
+     * Photo records around a point, nearest first; with a resolved imagery
+     * `filter`, only those of its projection uploaded since its cut-off.
+     */
+    async nearestPhotos({ lat, lon, filter = null }, { signal } = {}) {
+      const result = await photoApi(
+        '/2.0/photo/',
+        {
+          lat: lat.toFixed(7),
+          lng: lon.toFixed(7),
+          zoomLevel: String(NEAREST_SEARCH_ZOOM),
+          itemsPerPage: String(NEAREST_LIMIT),
+          ...photoFilterParams(filter),
+        },
+        { signal },
+      );
+      return Array.isArray(result.data) ? result.data : [];
+    },
+
+    /** One photo record. */
+    async getPhoto(photoId, { signal } = {}) {
+      const result = await photoApi(
+        `/2.0/photo/${encodeURIComponent(photoId)}`,
+        null,
+        { signal },
+      );
+      if (!result.data || typeof result.data !== 'object')
+        throw new KartaViewSourceError('KartaView has no such photo');
+      return result.data;
+    },
+
+    /** How many photos a sequence has, or null if KartaView does not say. */
+    async getSequenceCount(sequenceId, { signal } = {}) {
+      const result = await photoApi(
+        `/2.0/sequence/${encodeURIComponent(sequenceId)}`,
+        null,
+        { signal },
+      );
+      const count = Number(result.data?.countActivePhotos);
+      return Number.isFinite(count) && count > 0 ? count : null;
+    },
+
+    /** A page of a sequence's photos in capture order (1-based `page`). */
+    async getSequencePhotos(
+      sequenceId,
+      { page, itemsPerPage },
+      { signal } = {},
+    ) {
+      const result = await photoApi(
+        `/2.0/sequence/${encodeURIComponent(sequenceId)}/photos`,
+        { page: String(page), itemsPerPage: String(itemsPerPage) },
+        { signal },
+        {
+          gate: pageLimiter,
+          timeoutMs: PAGE_TIMEOUT_MS,
+          firstTimeoutMs: PAGE_TIMEOUT_MS,
+        },
+      );
+      return {
+        photos: Array.isArray(result.data) ? result.data : [],
+        hasMore: result.hasMoreData === true,
+      };
+    },
+  };
+}

src/layers/streetLevel/providers/kartaview/source.test.mjs

@@ -0,0 +1,728 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import {
+  KartaViewSourceError,
+  createKartaViewSource,
+  createLimiter,
+} from './source.js';
+import {
+  MASK_ATTEMPTS,
+  MASK_SLOW_MESSAGE,
+  NEAREST_LIMIT,
+  NEAREST_SEARCH_ZOOM,
+  PHOTO_API_CONCURRENCY,
+  PHOTO_API_RETRIES,
+  PHOTO_API_FIRST_TIMEOUT_MS,
+  PHOTO_API_TIMEOUT_MS,
+  PAGE_TIMEOUT_MS,
+  TILE_CONCURRENCY,
+} from './policy.js';
+
+/** A body streamed as browsers do, in `size`-byte chunks. */
+function streamed(text, size = 16_384) {
+  const bytes = new TextEncoder().encode(text);
+  let at = 0;
+  return {
+    getReader: () => ({
+      read: async () => {
+        if (at >= bytes.length) return { done: true };
+        const value = bytes.slice(at, at + size);
+        at += size;
+        return { done: false, value };
+      },
+      cancel: async () => {},
+    }),
+  };
+}
+
+// A 200 as browsers deliver it: streamed, so the code under test reads it
+// the way it does in production (`json` is there only to fail loudly).
+const ok = (body) => ({
+  ok: true,
+  status: 200,
+  headers: new Map(),
+  body: streamed(JSON.stringify(body)),
+  json: async () => {
+    throw new Error('a browser answer is read from its stream');
+  },
+});
+const status = (code, headers = new Map()) => ({
+  ok: false,
+  status: code,
+  headers,
+  json: async () => ({}),
+});
+const photoPayload = (data) => ({
+  status: { apiCode: 600, httpCode: 200 },
+  result: { data, hasMoreData: false },
+});
+
+test('coverage tiles come from api.kartaview.org as JSON', async () => {
+  const urls = [];
+  const source = createKartaViewSource({
+    fetchImpl: async (url) => {
+      urls.push(url);
+      return ok({ lines: [] });
+    },
+  });
+  assert.deepEqual(await source.getTile({ x: 4412, y: 6061, z: 14 }), {
+    lines: [],
+  });
+  assert.deepEqual(urls, [
+    'https://api.kartaview.org/2.0/sequence/tiles/4412/6061/14.json',
+  ]);
+});
+
+test('photo lookups run at most two at a time', async () => {
+  let running = 0;
+  let peak = 0;
+  const source = createKartaViewSource({
+    fetchImpl: async () => {
+      running++;
+      peak = Math.max(peak, running);
+      await new Promise((resolve) => setTimeout(resolve, 5));
+      running--;
+      return ok(photoPayload({ id: '1' }));
+    },
+  });
+  await Promise.all(
+    Array.from({ length: 7 }, (_, i) => source.getPhoto(String(i))),
+  );
+  assert.equal(peak, PHOTO_API_CONCURRENCY);
+});
+
+test('a 429 is retried after a wait, then answered', async () => {
+  let calls = 0;
+  const source = createKartaViewSource({
+    retryBaseMs: 1,
+    fetchImpl: async () => {
+      calls++;
+      return calls < 3
+        ? status(429, new Map([['retry-after', '0']]))
+        : ok(photoPayload([{ id: '9' }]));
+    },
+  });
+  const records = await source.nearestPhotos({ lat: 42.3, lon: -83.04 });
+  assert.deepEqual(records, [{ id: '9' }]);
+  assert.equal(calls, 3);
+});
+
+test('rate-limiting that outlasts the retries is reported with a wait', async () => {
+  let calls = 0;
+  const source = createKartaViewSource({
+    retryBaseMs: 1,
+    fetchImpl: async () => {
+      calls++;
+      return status(429, new Map([['retry-after', '0.001']]));
+    },
+  });
+  await assert.rejects(source.getPhoto('1'), (error) => {
+    assert.ok(error instanceof KartaViewSourceError);
+    assert.equal(error.status, 429);
+    assert.ok(error.retryAfterSec > 0);
+    assert.match(error.message, /try again in a moment/);
+    return true;
+  });
+  assert.equal(calls, PHOTO_API_RETRIES + 1);
+});
+
+test('an API refusal inside a 200 is a readable error with its code; 601 is just empty', async () => {
+  const refusing = createKartaViewSource({
+    fetchImpl: async () =>
+      ok({
+        status: { apiCode: 612, apiMessage: ' out of range ', httpCode: 400 },
+        result: {},
+      }),
+  });
+  await assert.rejects(
+    refusing.getPhoto('1'),
+    /KartaView refused the request \(code 612\)/,
+  );
+  const empty = createKartaViewSource({
+    fetchImpl: async () =>
+      ok({ status: { apiCode: 601 }, result: { data: [] } }),
+  });
+  assert.deepEqual(await empty.nearestPhotos({ lat: 0, lon: 0 }), []);
+  const page = await empty.getSequencePhotos('2008', {
+    page: 2,
+    itemsPerPage: 1000,
+  });
+  assert.deepEqual(page, { photos: [], hasMore: false });
+});
+
+test('HTTP errors, network failures and non-JSON become readable errors', async () => {
+  const http = createKartaViewSource({ fetchImpl: async () => status(500) });
+  await assert.rejects(http.getTile({ x: 0, y: 0, z: 14 }), /HTTP 500/);
+  let asked = 0;
+  const offline = createKartaViewSource({
+    fetchImpl: async () => {
+      asked++;
+      throw new TypeError('Failed to fetch');
+    },
+  });
+  // Not a timeout: no network is said as much, and not asked again at once.
+  await assert.rejects(
+    offline.getPhoto('1'),
+    /could not be reached — check the network/,
+  );
+  assert.equal(asked, 1);
+  const garbled = createKartaViewSource({
+    fetchImpl: async () => ({
+      ok: true,
+      status: 200,
+      headers: new Map(),
+      json: async () => {
+        throw new SyntaxError('Unexpected token <');
+      },
+    }),
+  });
+  await assert.rejects(
+    garbled.getTile({ x: 0, y: 0, z: 14 }),
+    /could not be read/,
+  );
+  const torn = createKartaViewSource({
+    fetchImpl: async () => ({
+      ok: true,
+      status: 200,
+      headers: new Map(),
+      body: streamed('{"lines": [', 4),
+    }),
+  });
+  await assert.rejects(
+    torn.getTile({ x: 0, y: 0, z: 14 }),
+    /could not be read/,
+  );
+});
+
+test('an abort stops a queued lookup without fetching, and wins over a retry wait', async () => {
+  let calls = 0;
+  let release;
+  const gate = new Promise((resolve) => (release = resolve));
+  const source = createKartaViewSource({
+    retryBaseMs: 10_000,
+    fetchImpl: async (url) => {
+      calls++;
+      if (url.includes('/slow')) await gate;
+      return status(429);
+    },
+  });
+  // Two slow lookups fill the queue; the third waits for a slot.
+  const first = new AbortController();
+  const slow = [
+    source.getPhoto('slow', { signal: first.signal }),
+    source.getPhoto('slow', { signal: first.signal }),
+  ];
+  const controller = new AbortController();
+  const queued = source.getPhoto('queued', { signal: controller.signal });
+  controller.abort(new Error('overtaken'));
+  await assert.rejects(queued, /overtaken/);
+  assert.equal(calls, 2, 'the queued lookup never fetched');
+  release();
+  // Each slow one is now waiting 10 s to retry; nothing else is asked.
+  const retrying = new AbortController();
+  const waiting = source.getPhoto('slow', { signal: retrying.signal });
+  await new Promise((resolve) => setTimeout(resolve, 20));
+  retrying.abort(new Error('closed'));
+  await assert.rejects(waiting, /closed/);
+  // The two first lookups are still waiting out their backoff: drop them.
+  first.abort(new Error('done'));
+  for (const promise of slow) await assert.rejects(promise, /done/);
+});
+
+test('the limiter runs tasks in order and keeps going after a failure', async () => {
+  const limiter = createLimiter(1);
+  const order = [];
+  const failing = limiter.run(async () => {
+    order.push('a');
+    throw new Error('a failed');
+  });
+  const second = limiter.run(async () => {
+    order.push('b');
+    return 'b';
+  });
+  await assert.rejects(failing, /a failed/);
+  assert.equal(await second, 'b');
+  assert.deepEqual(order, ['a', 'b']);
+  await new Promise((resolve) => setTimeout(resolve, 0));
+  assert.equal(limiter.pending, 0);
+});
+
+test('tiles, lookups and sequence pages queue separately, so a lookup never waits behind them', async () => {
+  const running = { tile: 0, photo: 0, page: 0 };
+  const peak = { tile: 0, photo: 0, page: 0 };
+  const release = [];
+  const kind = (url) =>
+    url.includes('/tiles/')
+      ? 'tile'
+      : url.includes('/photos')
+        ? 'page'
+        : 'photo';
+  const source = createKartaViewSource({
+    fetchImpl: async (url) => {
+      const k = kind(url);
+      running[k]++;
+      peak[k] = Math.max(peak[k], running[k]);
+      if (k !== 'photo') await new Promise((resolve) => release.push(resolve));
+      running[k]--;
+      return k === 'tile' ? ok({ lines: [] }) : ok(photoPayload([]));
+    },
+  });
+  const tiles = Array.from({ length: 9 }, (_, i) =>
+    source.getTile({ x: i, y: 0, z: 14 }),
+  );
+  const pages = [1, 2].map((page) =>
+    source.getSequencePhotos('1', { page, itemsPerPage: 500 }),
+  );
+  // Every slow tile and page is in flight or queued; a lookup still answers.
+  assert.deepEqual(await source.nearestPhotos({ lat: 1, lon: 1 }), []);
+  assert.equal(peak.tile, TILE_CONCURRENCY);
+  assert.equal(peak.page, 1);
+  while (release.length) {
+    release.shift()();
+    await new Promise((resolve) => setTimeout(resolve, 0));
+  }
+  await Promise.all([...tiles, ...pages]);
+  assert.equal(peak.tile, TILE_CONCURRENCY);
+  assert.equal(peak.page, 1);
+});
+
+test('a lookup that times out is asked once more, then reported as no answer in time', async (t) => {
+  t.mock.timers.enable({ apis: ['setTimeout'] });
+  let calls = 0;
+  const outcome = await onMockClock(t, () =>
+    createKartaViewSource({
+      fetchImpl: (url, { signal }) => {
+        calls++;
+        return new Promise((resolve, reject) =>
+          signal.addEventListener('abort', () => reject(signal.reason)),
+        );
+      },
+    }).getPhoto('1'),
+  );
+  assert.match(
+    String(outcome?.error?.message),
+    /did not answer in time — try again/,
+  );
+  assert.equal(outcome.error.timedOut, true);
+  assert.equal(calls, 2);
+});
+
+test('an image probe reads only the status: an archived photo (409) is not showable', async () => {
+  const seen = [];
+  const source = createKartaViewSource({
+    fetchImpl: async (url, { signal }) => {
+      seen.push(signal);
+      return {
+        ok: !url.includes('archived'),
+        status: url.includes('archived') ? 409 : 200,
+      };
+    },
+  });
+  assert.equal(
+    await source.probeImage('https://storage13.openstreetcam.org/ok.jpg'),
+    true,
+  );
+  assert.equal(
+    await source.probeImage('https://storage13.openstreetcam.org/archived.jpg'),
+    false,
+  );
+  assert.equal(await source.probeImage(null), false);
+  assert.ok(
+    seen.every((signal) => signal.aborted),
+    'the body is dropped',
+  );
+  const offline = createKartaViewSource({
+    fetchImpl: async () => {
+      throw new TypeError('Failed to fetch');
+    },
+  });
+  // No answer is not an answer: the caller may try again later.
+  assert.equal(
+    await offline.probeImage('https://x.openstreetcam.org/a.jpg'),
+    null,
+  );
+  const busy = createKartaViewSource({
+    fetchImpl: async () => ({ ok: false, status: 502 }),
+  });
+  assert.equal(
+    await busy.probeImage('https://x.openstreetcam.org/a.jpg'),
+    null,
+  );
+});
+
+test('a cold tile that times out is asked once more; an unreachable one is not', async (t) => {
+  t.mock.timers.enable({ apis: ['setTimeout'] });
+  let calls = 0;
+  const outcome = await onMockClock(t, () =>
+    createKartaViewSource({
+      fetchImpl: (url, { signal }) => {
+        calls++;
+        if (calls === 1)
+          return new Promise((resolve, reject) =>
+            signal.addEventListener('abort', () => reject(signal.reason)),
+          );
+        return Promise.resolve(ok({ lines: [] }));
+      },
+    }).getTile({ x: 1, y: 2, z: 13 }),
+  );
+  assert.deepEqual(outcome.value, { lines: [] });
+  assert.equal(calls, 2);
+  let asked = 0;
+  const offline = createKartaViewSource({
+    fetchImpl: async () => {
+      asked++;
+      throw new TypeError('Failed to fetch');
+    },
+  });
+  await assert.rejects(
+    offline.getTile({ x: 1, y: 2, z: 13 }),
+    /could not be reached/,
+  );
+  assert.equal(asked, 1);
+});
+
+test('an absurdly large answer is refused before it is parsed', async () => {
+  let parsed = false;
+  const source = createKartaViewSource({
+    fetchImpl: async () => ({
+      ok: true,
+      status: 200,
+      headers: new Map([['content-length', String(64 * 1024 * 1024)]]),
+      json: async () => {
+        parsed = true;
+        return { lines: [] };
+      },
+    }),
+  });
+  await assert.rejects(source.getTile({ x: 1, y: 2, z: 13 }), /too much data/);
+  assert.equal(parsed, false);
+});
+
+test('sequence pages run one at a time, the newest first', async () => {
+  const order = [];
+  let release;
+  const gate = new Promise((resolve) => (release = resolve));
+  const source = createKartaViewSource({
+    fetchImpl: async (url) => {
+      const page = new URL(url).searchParams.get('page');
+      order.push(page);
+      if (page === '1') await gate;
+      return ok(photoPayload([]));
+    },
+  });
+  const pages = ['1', '2', '3'].map((page) =>
+    source.getSequencePhotos('9', { page, itemsPerPage: 250 }),
+  );
+  await new Promise((resolve) => setTimeout(resolve, 0));
+  release();
+  await Promise.all(pages);
+  assert.deepEqual(order, ['1', '3', '2']);
+});
+
+/** Every pending promise callback, without moving the mocked clock. */
+const flush = () => new Promise((resolve) => setImmediate(resolve));
+
+/**
+ * Run `call` on the mocked clock in 100 ms steps until it settles (60 s at
+ * most). `stamp()` reads the clock, for a fetch to record when it was asked.
+ */
+async function onMockClock(t, call, { until = 60_000 } = {}) {
+  let now = 0;
+  const stamp = () => now;
+  let outcome = null;
+  const promise = call(stamp);
+  promise.then(
+    (value) => (outcome = { value, at: now }),
+    (error) => (outcome = { error, at: now }),
+  );
+  while (!outcome && now < until) {
+    await flush();
+    if (outcome) break;
+    t.mock.timers.tick(100);
+    now += 100;
+  }
+  await flush();
+  return outcome;
+}
+
+test('429 waits double from 0.8 s, wait out a longer Retry-After up to 10 s, and 2 s without one', async (t) => {
+  t.mock.timers.enable({ apis: ['setTimeout'] });
+  async function waits(retryAfter) {
+    const asked = [];
+    const headers = new Map(
+      retryAfter === undefined ? [] : [['retry-after', retryAfter]],
+    );
+    const outcome = await onMockClock(t, (stamp) =>
+      createKartaViewSource({
+        fetchImpl: async () => {
+          asked.push(stamp());
+          return asked.length <= PHOTO_API_RETRIES
+            ? status(429, headers)
+            : ok(photoPayload({ id: '1' }));
+        },
+      }).getPhoto('1'),
+    );
+    assert.deepEqual(outcome?.value, { id: '1' }, `answered (${retryAfter})`);
+    return asked.slice(1).map((at, i) => at - asked[i]);
+  }
+  assert.deepEqual(await waits('0'), [800, 1600, 3200], 'doubling backoff');
+  assert.deepEqual(await waits('5'), [5000, 5000, 5000], 'Retry-After wins');
+  assert.deepEqual(await waits('30'), [10_000, 10_000, 10_000], 'capped');
+  assert.deepEqual(await waits(undefined), [2000, 2000, 3200], 'assumed 2 s');
+});
+
+test('a lookup that hangs is given up after a short first try, then the full timeout, then reported', async (t) => {
+  t.mock.timers.enable({ apis: ['setTimeout'] });
+  const asked = [];
+  const outcome = await onMockClock(t, (stamp) =>
+    createKartaViewSource({
+      fetchImpl: (url, { signal }) => {
+        asked.push(stamp());
+        return new Promise((resolve, reject) =>
+          signal.addEventListener('abort', () => reject(signal.reason)),
+        );
+      },
+    }).getPhoto('1'),
+  );
+  assert.deepEqual(asked, [0, PHOTO_API_FIRST_TIMEOUT_MS]);
+  assert.match(String(outcome?.error?.message), /did not answer in time/);
+  assert.equal(outcome.at, PHOTO_API_FIRST_TIMEOUT_MS + PHOTO_API_TIMEOUT_MS);
+});
+
+test('the nearest lookup asks for the few photos around the point at the search zoom', async () => {
+  const urls = [];
+  const source = createKartaViewSource({
+    fetchImpl: async (url) => {
+      urls.push(new URL(url));
+      return ok(photoPayload([]));
+    },
+  });
+  await source.nearestPhotos({ lat: 42.33, lon: -83.04 });
+  assert.equal(urls[0].pathname, '/2.0/photo/');
+  assert.deepEqual(Object.fromEntries(urls[0].searchParams), {
+    lat: '42.3300000',
+    lng: '-83.0400000',
+    zoomLevel: String(NEAREST_SEARCH_ZOOM),
+    itemsPerPage: String(NEAREST_LIMIT),
+  });
+  assert.equal(NEAREST_SEARCH_ZOOM, 18);
+  assert.equal(NEAREST_LIMIT, 10);
+});
+
+test('a chunked answer with no length is cut off once it grows past the cap', async () => {
+  let reads = 0;
+  let cancelled = false;
+  const chunk = new Uint8Array(6 * 1024 * 1024);
+  const source = createKartaViewSource({
+    fetchImpl: async () => ({
+      ok: true,
+      status: 200,
+      headers: new Map(),
+      body: {
+        getReader: () => ({
+          read: async () =>
+            ++reads > 10 ? { done: true } : { done: false, value: chunk },
+          cancel: async () => {
+            cancelled = true;
+          },
+        }),
+      },
+    }),
+  });
+  await assert.rejects(source.getTile({ x: 1, y: 2, z: 13 }), /too much data/);
+  assert.equal(reads, 3, 'stopped at the third 6 MB chunk');
+  assert.equal(cancelled, true);
+  const small = createKartaViewSource({
+    fetchImpl: async () => {
+      const bytes = new TextEncoder().encode('{"lines":[]}');
+      let given = false;
+      return {
+        ok: true,
+        status: 200,
+        headers: new Map(),
+        body: {
+          getReader: () => ({
+            read: async () =>
+              given
+                ? { done: true }
+                : ((given = true), { done: false, value: bytes }),
+            cancel: async () => {},
+          }),
+        },
+      };
+    },
+  });
+  assert.deepEqual(await small.getTile({ x: 1, y: 2, z: 13 }), { lines: [] });
+});
+
+test('a chunked answer split mid-character is reassembled in order', async () => {
+  const payload = {
+    lines: [
+      {
+        track: [{ lat: '1', lng: '2' }],
+        name: 'Strada Memorandumului — Cluj-Napoca 😀',
+      },
+    ],
+    note: 'ăîşţ'.repeat(200),
+  };
+  const source = createKartaViewSource({
+    fetchImpl: async () => ({
+      ok: true,
+      status: 200,
+      headers: new Map(),
+      // 3-byte chunks cut multi-byte characters in two.
+      body: streamed(JSON.stringify(payload), 3),
+    }),
+  });
+  assert.deepEqual(await source.getTile({ x: 1, y: 2, z: 13 }), payload);
+});
+
+test('a sequence page gets the full 30 s on its first try, then 30 s once more', async (t) => {
+  t.mock.timers.enable({ apis: ['setTimeout'] });
+  const asked = [];
+  const outcome = await onMockClock(
+    t,
+    (stamp) =>
+      createKartaViewSource({
+        fetchImpl: (url, { signal }) => {
+          asked.push(stamp());
+          return new Promise((resolve, reject) =>
+            signal.addEventListener('abort', () => reject(signal.reason)),
+          );
+        },
+      }).getSequencePhotos('9', { page: 1, itemsPerPage: 250 }),
+    { until: 120_000 },
+  );
+  assert.deepEqual(asked, [0, PAGE_TIMEOUT_MS]);
+  assert.match(String(outcome?.error?.message), /did not answer in time/);
+  assert.equal(outcome.at, 2 * PAGE_TIMEOUT_MS);
+});
+
+test('an answer turned away unread (an error, a 429, a length past the cap) lets its connection go', async () => {
+  /** A response whose body is never read: records its cancel and the abort. */
+  const unread = (answer) => {
+    const seen = { cancelled: false, signal: null };
+    const fetchImpl = async (url, { signal }) => {
+      seen.signal = signal;
+      return {
+        ...answer,
+        body: {
+          locked: false,
+          getReader: () => {
+            throw new Error('not read');
+          },
+          cancel: async () => {
+            seen.cancelled = true;
+          },
+        },
+      };
+    };
+    return { seen, fetchImpl };
+  };
+  const cases = [
+    [{ ok: false, status: 503, headers: new Map() }, /HTTP 503/],
+    [
+      {
+        ok: true,
+        status: 200,
+        headers: new Map([['content-length', String(64 * 1024 * 1024)]]),
+      },
+      /too much data/,
+    ],
+  ];
+  for (const [answer, message] of cases) {
+    const { seen, fetchImpl } = unread(answer);
+    const source = createKartaViewSource({ fetchImpl });
+    await assert.rejects(source.getTile({ x: 1, y: 2, z: 13 }), message);
+    assert.equal(seen.signal.aborted, true, `${message}: request aborted`);
+    assert.equal(seen.cancelled, true, `${message}: body cancelled`);
+  }
+  // A 429 is let go before its retry is asked.
+  const { seen, fetchImpl } = unread({
+    ok: false,
+    status: 429,
+    headers: new Map([['retry-after', '0']]),
+  });
+  const signals = [];
+  const source = createKartaViewSource({
+    fetchImpl: async (url, init) => {
+      signals.push(init.signal);
+      if (signals.length === 1) return fetchImpl(url, init);
+      return ok(photoPayload([]));
+    },
+  });
+  await source.getPhoto('1');
+  assert.equal(signals[0].aborted, true);
+  assert.equal(seen.cancelled, true);
+  assert.equal(signals[1].aborted, false, 'a read answer is left alone');
+});
+
+test('a filtered tile comes as PNG bytes; KartaView still drawing it (504) is asked again, then given up', async () => {
+  const png = new Uint8Array([137, 80, 78, 71, 1, 2, 3]);
+  const bytesOf = () => ({
+    ok: true,
+    status: 200,
+    headers: new Map(),
+    body: {
+      getReader: () => {
+        let given = false;
+        return {
+          read: async () =>
+            given
+              ? { done: true }
+              : ((given = true), { done: false, value: png }),
+          cancel: async () => {},
+        };
+      },
+    },
+  });
+  const urls = [];
+  let answers = [status(504), status(503), bytesOf()];
+  const source = createKartaViewSource({
+    maskRetryMs: 0,
+    fetchImpl: async (url) => {
+      urls.push(url);
+      return answers.shift();
+    },
+  });
+  const tile = { x: 13054, y: 8474, z: 14 };
+  assert.deepEqual(await source.getTileMask(tile, 'fieldOfView=360'), png);
+  assert.deepEqual(urls, [
+    'https://api.kartaview.org/2.0/sequence/tiles/13054/8474/14.png?fieldOfView=360',
+    'https://api.kartaview.org/2.0/sequence/tiles/13054/8474/14.png?fieldOfView=360',
+    'https://api.kartaview.org/2.0/sequence/tiles/13054/8474/14.png?fieldOfView=360',
+  ]);
+  // Still drawing after every try: given up, saying so.
+  urls.length = 0;
+  answers = Array.from({ length: 10 }, () => status(504));
+  await assert.rejects(source.getTileMask(tile, 'fieldOfView=360'), {
+    message: MASK_SLOW_MESSAGE,
+    timedOut: true,
+  });
+  assert.equal(urls.length, MASK_ATTEMPTS);
+  // A refusal is not asked again.
+  urls.length = 0;
+  answers = [status(400)];
+  await assert.rejects(source.getTileMask(tile, 'fieldOfView=360'), /HTTP 400/);
+  assert.equal(urls.length, 1);
+});
+
+test('a filtered nearest search asks KartaView for the projection and upload date', async () => {
+  const urls = [];
+  const source = createKartaViewSource({
+    fetchImpl: async (url) => {
+      urls.push(new URL(url));
+      return ok(photoPayload([]));
+    },
+  });
+  await source.nearestPhotos({
+    lat: 42.3314,
+    lon: -83.0458,
+    filter: { pano: 'pano', sinceMs: Date.UTC(2026, 0, 2, 12) },
+  });
+  await source.nearestPhotos({ lat: 42.3314, lon: -83.0458 });
+  assert.equal(urls[0].searchParams.get('projection'), 'SPHERE');
+  assert.equal(urls[0].searchParams.get('startDate'), '2026-01-02');
+  assert.equal(urls[1].searchParams.has('projection'), false);
+  assert.equal(urls[1].searchParams.has('startDate'), false);
+});

src/layers/streetLevel/providers/kartaview/viewer.js

@@ -0,0 +1,698 @@
+import {
+  createPanoramaRenderer,
+  PANO_FOV_DEFAULT_DEG,
+  wrapDegrees,
+} from './panorama.js';
+import {
+  FLAT_FULL_SIZE,
+  FLAT_VIEW_SIZE,
+  IMAGE_TIMEOUT_MS,
+  KARTAVIEW_PROVIDER_ID,
+  PANO_FULL_SIZE,
+  PANO_MID_SIZE,
+  PANO_PREVIEW_SIZE,
+  cameraBearing,
+  kartaViewPhotoUrl,
+  resizedImageUrl,
+} from './policy.js';
+
+const LOAD_FAILED = 'The KartaView photo could not be loaded';
+
+/**
+ * Load an image within the timeout. A CORS-clean one (for WebGL) is decoded
+ * off the main thread into an ImageBitmap where the browser can: uploading
+ * a decoded bitmap costs a fraction of uploading an <img> (90 ms → 15 ms for
+ * 4096×2048 on a phone-class CPU).
+ */
+export function loadImage(
+  url,
+  { crossOrigin = true, timeoutMs = IMAGE_TIMEOUT_MS } = {},
+) {
+  if (
+    crossOrigin &&
+    url &&
+    typeof globalThis.createImageBitmap === 'function' &&
+    typeof globalThis.fetch === 'function'
+  )
+    return loadBitmap(url, timeoutMs);
+  return new Promise((resolve, reject) => {
+    if (!url) return reject(new Error(LOAD_FAILED));
+    const image = new Image();
+    if (crossOrigin) image.crossOrigin = 'anonymous';
+    image.decoding = 'async';
+    const timer = setTimeout(() => {
+      image.src = '';
+      reject(new Error(LOAD_FAILED));
+    }, timeoutMs);
+    image.onload = () => {
+      clearTimeout(timer);
+      resolve(image);
+    };
+    image.onerror = () => {
+      clearTimeout(timer);
+      reject(new Error(LOAD_FAILED));
+    };
+    image.src = url;
+  });
+}
+
+async function loadBitmap(url, timeoutMs) {
+  const controller = new AbortController();
+  const timer = setTimeout(() => controller.abort(), timeoutMs);
+  try {
+    const response = await fetch(url, {
+      mode: 'cors',
+      signal: controller.signal,
+    });
+    if (!response.ok) throw new Error(LOAD_FAILED);
+    return await createImageBitmap(await response.blob());
+  } catch {
+    throw new Error(LOAD_FAILED);
+  } finally {
+    clearTimeout(timer);
+  }
+}
+
+/** Free a decoded bitmap nobody will draw (an <img> has nothing to free). */
+function release(image) {
+  image?.close?.();
+}
+
+/** The panorama size a canvas this wide can show sharply at this field of view. */
+export function panoSizeFor(canvasPixels, fovDeg) {
+  const needed = (Math.max(1, canvasPixels) * 360) / Math.max(1, fovDeg);
+  return needed > PANO_MID_SIZE[0] ? PANO_FULL_SIZE : PANO_MID_SIZE;
+}
+
+/**
+ * Viewer adapter for KartaView photos: a flat photo in an <img>, a 360°
+ * photo on a WebGL panorama (drag to look, wheel to zoom), and ‹ › to step
+ * along the sequence (also ← →). Poses follow the view direction.
+ *
+ * @param {object} options
+ * @param {(photoId: string) => Promise<object>} options.getPhoto   A normalized photo (policy.js normalizePhoto).
+ * @param {(photo: object, delta: -1|1) => Promise<string|null>} options.step   The photo `delta` along the sequence, or null at its end.
+ * @param {(imageId: string) => void} options.onStep   Open the photo ‹ › chose (through the core, so loading and errors show).
+ * @param {(photo: object) => void} [options.onShown]   A photo is on screen.
+ * @param {(imageId: string) => void} [options.onReopen]   Draw the same photo again after a GPU reset (default: `onStep`).
+ * @param {object} [options.render]   Render governor.
+ * @param {(url: string, options?: object) => Promise<HTMLImageElement>} [options.load]
+ * @param {(canvas: HTMLCanvasElement) => object} [options.createRenderer]
+ * @returns {import('../../registry.js').ViewerAdapter}
+ */
+export function createKartaViewViewer({
+  getPhoto,
+  step,
+  onStep,
+  onShown = () => {},
+  onReopen = onStep,
+  render,
+  load = loadImage,
+  createRenderer = createPanoramaRenderer,
+}) {
+  const listeners = new Set();
+  let root = null;
+  let picture = null;
+  let canvas = null;
+  let prevButton = null;
+  let nextButton = null;
+  let renderer = null;
+  /** WebGL failed once: 360° photos show their front view instead. */
+  let rendererFailed = false;
+  let photo = null;
+  /** What shows: 'flat', 'pano' or null. */
+  let showing = null;
+  let openSeq = 0;
+  let renderMode = 'letterbox';
+  let drag = null;
+  let poseFrame = 0;
+  let removeListeners = [];
+  /** The document the viewer was built in (new canvases come from it). */
+  let documentOf = null;
+  /** A context loss's look direction, for the reopen of that photo. */
+  let restoreView = null;
+  /** Width of the panorama texture on screen (0: the preview). */
+  let panoWidth = 0;
+  /** The flat photo on screen is the 2,560 px version. */
+  let flatSharp = false;
+  /** The sharper version loading ({seq, kind}): a resize starts no second one. */
+  let upgrading = null;
+  /** A resize came while it loaded: look again once it lands. */
+  let upgradeAgain = false;
+  /** The photo an open is fetching: ‹ › step on from it, not the old one. */
+  let openingId = null;
+  /** ‹ › chose this photo: keep the panorama's look direction for it. */
+  let keepViewFor = null;
+  /** ‹ › presses run one after another, each from where the last one went. */
+  let steps = Promise.resolve();
+
+  function requestRender() {
+    render?.governorRequestRender?.('kartaview-viewer');
+  }
+
+  function emit() {
+    if (!photo || !showing) return;
+    // A lost GPU context, still being recovered: the open that redraws the
+    // panorama poses once it is on screen.
+    if (showing === 'pano' && !renderer) return;
+    const view = showing === 'pano' ? renderer.getView() : null;
+    const heading = cameraBearing(photo);
+    const pose = {
+      providerId: KARTAVIEW_PROVIDER_ID,
+      imageId: photo.id,
+      position: { lon: photo.lon, lat: photo.lat },
+      bearing:
+        heading === null
+          ? null
+          : view
+            ? wrapDegrees(heading + view.yaw)
+            : heading,
+      tilt: view ? view.pitch : 0,
+      altitude: null,
+      isPano: showing === 'pano',
+      capturedAt: photo.capturedAt,
+      capturedAtPrecision: 'day',
+      // KartaView's only place name is the sequence's, where the drive began.
+      title: null,
+      creator: null,
+      sequenceId: photo.sequenceId,
+      externalUrl: kartaViewPhotoUrl(photo),
+    };
+    for (const listener of [...listeners]) {
+      try {
+        listener(pose);
+      } catch {
+        /* listener errors are the core's to log */
+      }
+    }
+    requestRender();
+  }
+
+  /** Re-emit on the next frame: a drag moves the view many times a frame. */
+  function emitSoon() {
+    if (poseFrame) return;
+    poseFrame = requestAnimationFrame(() => {
+      poseFrame = 0;
+      emit();
+    });
+  }
+
+  function syncButtons() {
+    const enabled = Boolean(photo?.sequenceId) && showing !== null;
+    if (prevButton) prevButton.disabled = !enabled;
+    if (nextButton) nextButton.disabled = !enabled;
+    if (enabled) checkEnds(photo);
+  }
+
+  /** Disable ‹ or › at once where the sequence ends (it also warms the neighbours). */
+  function checkEnds(target) {
+    for (const [delta, button] of [
+      [-1, prevButton],
+      [1, nextButton],
+    ])
+      step(target, delta).then(
+        (id) => {
+          if (photo === target && button && !id) disable(button);
+        },
+        () => {},
+      );
+  }
+
+  /** Disable a step button, keeping keyboard focus in the viewer. */
+  function disable(button) {
+    if (button.ownerDocument?.activeElement === button) root?.focus?.();
+    button.disabled = true;
+  }
+
+  function show(kind) {
+    showing = kind;
+    if (picture) picture.hidden = kind !== 'flat';
+    if (canvas) canvas.hidden = kind !== 'pano';
+    if (root) root.dataset.kind = kind || '';
+    syncButtons();
+  }
+
+  function applyRenderMode() {
+    if (picture)
+      picture.style.objectFit = renderMode === 'fill' ? 'cover' : 'contain';
+  }
+
+  function ensureRenderer() {
+    if (renderer || rendererFailed || !canvas) return renderer;
+    try {
+      renderer = createRenderer(canvas);
+    } catch {
+      rendererFailed = true;
+      renderer = null;
+    }
+    return renderer;
+  }
+
+  /**
+   * A lost WebGL context (GPU reset, memory pressure) takes the panorama
+   * with it: drop the renderer, and show the photo again on a new one.
+   */
+  function onContextLost(event) {
+    event.preventDefault?.();
+    const lost = renderer;
+    renderer = null;
+    // The new renderer starts facing the photo's heading: keep the user's look.
+    if (showing === 'pano' && photo && lost)
+      restoreView = { id: photo.id, view: lost.getView() };
+    try {
+      lost?.destroy();
+    } catch {
+      /* already gone */
+    }
+    // A lost canvas hands back its lost context: draw on a new element.
+    const fresh = makeCanvas(documentOf);
+    fresh.hidden = canvas.hidden;
+    canvas.replaceWith?.(fresh);
+    canvas = fresh;
+    // Show the photo again through the core, unless a newer one is opening.
+    if (showing === 'pano' && photo && openingId === null) {
+      const again = photo.id;
+      show(null);
+      openingId = again;
+      onReopen(again);
+    }
+  }
+
+  /** The panorama canvas, wired for drag, pinch, wheel and context loss. */
+  function makeCanvas(doc) {
+    const element = doc.createElement('canvas');
+    element.className = 'sl-kv-pano';
+    element.hidden = true;
+    listen(element, 'pointerdown', onPointerDown);
+    listen(element, 'pointermove', onPointerMove);
+    listen(element, 'pointerup', onPointerUp);
+    listen(element, 'pointercancel', onPointerUp);
+    listen(element, 'wheel', onWheel, { passive: false });
+    listen(element, 'webglcontextlost', onContextLost);
+    return element;
+  }
+
+  /**
+   * Step along the sequence from the photo showing, or from the one on its
+   * way after an earlier press, and open it through the core.
+   */
+  function stepBy(delta) {
+    steps = steps.then(async () => {
+      const fromId = openingId ?? photo?.id;
+      if (!fromId || !root) return;
+      let from;
+      let nextId = null;
+      try {
+        from = await getPhoto(fromId);
+        if (from.sequenceId) nextId = await step(from, delta);
+      } catch {
+        // Not the end of the sequence, just no answer: the press is lost.
+        return;
+      }
+      // Closed, or another photo was opened meanwhile.
+      if ((openingId ?? photo?.id) !== fromId) return;
+      if (!nextId) {
+        const button = delta < 0 ? prevButton : nextButton;
+        if (button && photo?.id === fromId) disable(button);
+        return;
+      }
+      openingId = nextId;
+      keepViewFor = nextId;
+      onStep(nextId);
+    });
+  }
+
+  /** Pointers on the panorama: one drags the view, two pinch the zoom. */
+  const pointers = new Map();
+  let pinch = null;
+
+  function pinchSpan() {
+    const [a, b] = [...pointers.values()];
+    return Math.max(1, Math.hypot(a.x - b.x, a.y - b.y));
+  }
+
+  function onPointerDown(event) {
+    if (showing !== 'pano' || !renderer) return;
+    if (event.pointerType === 'mouse' && event.button !== 0) return;
+    pointers.set(event.pointerId, { x: event.clientX, y: event.clientY });
+    canvas.setPointerCapture?.(event.pointerId);
+    if (pointers.size === 2) {
+      drag = null;
+      pinch = { span: pinchSpan(), fov: renderer.getView().fov };
+      return;
+    }
+    drag = {
+      id: event.pointerId,
+      x: event.clientX,
+      y: event.clientY,
+      view: renderer.getView(),
+    };
+    canvas.classList.add('sl-kv-dragging');
+  }
+
+  function onPointerMove(event) {
+    if (pointers.has(event.pointerId))
+      pointers.set(event.pointerId, { x: event.clientX, y: event.clientY });
+    if (pinch && pointers.size === 2 && renderer) {
+      renderer.setView({ fov: pinch.fov * (pinch.span / pinchSpan()) });
+      return;
+    }
+    if (!drag || event.pointerId !== drag.id || !renderer) return;
+    const { fov } = drag.view;
+    const width = Math.max(1, canvas.clientWidth);
+    const height = Math.max(1, canvas.clientHeight);
+    const vertical = fov;
+    const horizontal = fov * (width / height);
+    renderer.setView({
+      yaw: drag.view.yaw - ((event.clientX - drag.x) / width) * horizontal,
+      pitch: drag.view.pitch + ((event.clientY - drag.y) / height) * vertical,
+    });
+    emitSoon();
+  }
+
+  function onPointerUp(event) {
+    pointers.delete(event.pointerId);
+    if (pointers.size < 2) pinch = null;
+    if (!drag || event.pointerId !== drag.id) return;
+    drag = null;
+    canvas.classList.remove('sl-kv-dragging');
+  }
+
+  function onWheel(event) {
+    if (showing !== 'pano' || !renderer) return;
+    event.preventDefault();
+    const { fov } = renderer.getView();
+    renderer.setView({ fov: fov * Math.exp(event.deltaY * 0.001) });
+  }
+
+  function onKeyDown(event) {
+    if (
+      event.defaultPrevented ||
+      event.altKey ||
+      event.ctrlKey ||
+      event.metaKey
+    )
+      return;
+    const pano = showing === 'pano' && renderer;
+    const turn = { ArrowLeft: -1, ArrowRight: 1 }[event.key];
+    // Shift+← → look around a panorama; ← → step along the sequence.
+    if (turn && event.shiftKey && pano) {
+      event.preventDefault();
+      const { yaw, fov } = renderer.getView();
+      renderer.setView({ yaw: yaw + (turn * fov) / 4 });
+      emitSoon();
+    } else if (turn) {
+      event.preventDefault();
+      stepBy(turn);
+    } else if ((event.key === 'ArrowUp' || event.key === 'ArrowDown') && pano) {
+      event.preventDefault();
+      const { pitch, fov } = renderer.getView();
+      renderer.setView({
+        pitch: pitch + ((event.key === 'ArrowUp' ? 1 : -1) * fov) / 6,
+      });
+      emitSoon();
+    } else if (['+', '=', '-', '_'].includes(event.key) && pano) {
+      event.preventDefault();
+      const { fov } = renderer.getView();
+      renderer.setView({
+        fov: fov * (event.key === '+' || event.key === '=' ? 0.85 : 1 / 0.85),
+      });
+    }
+  }
+
+  function listen(target, type, handler, options) {
+    target.addEventListener(type, handler, options);
+    removeListeners.push(() =>
+      target.removeEventListener(type, handler, options),
+    );
+  }
+
+  function build(host) {
+    const doc = host.ownerDocument;
+    documentOf = doc;
+    root = doc.createElement('div');
+    root.className = 'sl-kv-viewer';
+    root.tabIndex = 0;
+    root.setAttribute('role', 'group');
+    root.setAttribute(
+      'aria-label',
+      'KartaView photo. ← and → step along the sequence. On a 360° photo, drag or use Shift+← →, ↑ ↓ to look around, and + − to zoom',
+    );
+    picture = doc.createElement('img');
+    picture.className = 'sl-kv-photo';
+    picture.alt = 'KartaView street-level photo';
+    picture.draggable = false;
+    picture.hidden = true;
+    canvas = makeCanvas(doc);
+    const nav = (label, glyph, delta) => {
+      const button = doc.createElement('button');
+      button.type = 'button';
+      button.className = `sl-kv-step sl-kv-step-${delta < 0 ? 'prev' : 'next'}`;
+      button.textContent = glyph;
+      button.title = label;
+      button.setAttribute('aria-label', label);
+      button.disabled = true;
+      listen(button, 'click', (event) => {
+        event.stopPropagation();
+        stepBy(delta);
+      });
+      return button;
+    };
+    prevButton = nav('Previous photo in this sequence (←)', '‹', -1);
+    nextButton = nav('Next photo in this sequence (→)', '›', 1);
+    root.append(picture, canvas, prevButton, nextButton);
+    host.append(root);
+    listen(root, 'keydown', onKeyDown);
+    applyRenderMode();
+  }
+
+  function teardown() {
+    pointers.clear();
+    pinch = null;
+    for (const remove of removeListeners) remove();
+    removeListeners = [];
+    if (poseFrame) cancelAnimationFrame(poseFrame);
+    poseFrame = 0;
+    drag = null;
+    renderer?.destroy();
+    renderer = null;
+    root?.remove();
+    root = picture = canvas = prevButton = nextButton = null;
+    showing = null;
+    photo = null;
+  }
+
+  /** A sharper version once the first is on screen, if nothing replaced it. */
+  async function upgrade(target, seq, kind) {
+    // A 360° photo shown flat (no WebGL) keeps its front view.
+    if (kind === 'flat' && target.isPano) return;
+    const size = kind === 'pano' ? panoSizeNow() : FLAT_FULL_SIZE;
+    if (kind === 'pano' && size[0] <= panoWidth) return;
+    // A docked viewer shows the 1,280 px version in full: the 2,560 px one
+    // (~0.6 MB a photo) waits until the viewer is bigger than that.
+    if (kind === 'flat' && (flatSharp || flatPixels() <= FLAT_VIEW_SIZE[0]))
+      return;
+    const url =
+      kind === 'pano'
+        ? resizedImageUrl(target.urls.pano, size)
+        : resizedImageUrl(target.urls.full, size);
+    if (!url) return;
+    // Resizes come in bursts while the panel animates: one load at a time
+    // for this photo, and one more look once it lands.
+    if (upgrading?.seq === seq && upgrading.kind === kind) {
+      upgradeAgain = true;
+      return;
+    }
+    const pending = (upgrading = { seq, kind });
+    upgradeAgain = false;
+    let image = null;
+    try {
+      image = await load(url, { crossOrigin: kind === 'pano' });
+      if (seq !== openSeq || photo !== target || showing !== kind) return;
+      if (kind === 'pano') {
+        if (!renderer || size[0] <= panoWidth) return;
+        renderer.setImage(image);
+        image = null;
+        panoWidth = size[0];
+      } else {
+        picture.src = image.src;
+        image = null;
+        flatSharp = true;
+      }
+      requestRender();
+    } catch {
+      /* the first version stays */
+    } finally {
+      release(image);
+      if (upgrading === pending) {
+        upgrading = null;
+        if (upgradeAgain && seq === openSeq && photo === target) {
+          upgradeAgain = false;
+          upgrade(target, seq, showing);
+        }
+      }
+    }
+  }
+
+  /** Device pixels across the flat photo's frame. */
+  function flatPixels() {
+    const ratio = globalThis.devicePixelRatio || 1;
+    return (
+      Math.max(picture?.clientWidth || 0, picture?.clientHeight || 0) * ratio
+    );
+  }
+
+  /** The sharp panorama this viewer needs now: 2,048 docked, 4,096 expanded. */
+  function panoSizeNow() {
+    const ratio = Math.min(globalThis.devicePixelRatio || 1, 2);
+    const width = (canvas?.clientWidth || 0) * ratio;
+    return panoSizeFor(width, renderer?.getView().fov ?? PANO_FOV_DEFAULT_DEG);
+  }
+
+  async function showPano(target, seq, keepView) {
+    // Only the proxy can shrink a 13,000 px panorama: if it fails, the
+    // caller shows the front view rather than waiting on it twice.
+    const image = await load(
+      resizedImageUrl(target.urls.pano, PANO_PREVIEW_SIZE),
+      { crossOrigin: true },
+    );
+    if (seq !== openSeq) {
+      release(image);
+      return false;
+    }
+    // The context may have been lost while this loaded: build on the new
+    // canvas, or let the caller show the front view.
+    if (!ensureRenderer()) {
+      release(image);
+      throw new Error(LOAD_FAILED);
+    }
+    const restore = restoreView?.id === target.id ? restoreView.view : null;
+    restoreView = null;
+    if (restore) renderer.setView(restore);
+    else if (!keepView || showing !== 'pano')
+      renderer.setView({ yaw: 0, pitch: 0, fov: PANO_FOV_DEFAULT_DEG });
+    photo = target;
+    // Shown first: a hidden canvas measures 0 and would be sized 1×1.
+    show('pano');
+    renderer.setImage(image);
+    panoWidth = 0;
+    return true;
+  }
+
+  async function showFlat(target, seq) {
+    // The proxy's 1,280 px version is a few hundred kB; KartaView's own
+    // "large thumbnail" can be 1.7 MB. Either serves when the other fails.
+    // A 360° photo's front view is only on storage.
+    const proxied = target.isPano
+      ? null
+      : resizedImageUrl(target.urls.full, FLAT_VIEW_SIZE);
+    const sources = [proxied, target.urls.view].filter(Boolean);
+    let image;
+    let failure = null;
+    for (const url of sources) {
+      try {
+        image = await load(url, { crossOrigin: false });
+        break;
+      } catch (error) {
+        failure = error;
+        if (seq !== openSeq) return false;
+      }
+    }
+    if (!image) throw failure || new Error(LOAD_FAILED);
+    if (seq !== openSeq) return false;
+    picture.src = image.src;
+    flatSharp = false;
+    photo = target;
+    show('flat');
+    return true;
+  }
+
+  async function openPhoto(id, seq, keepView) {
+    const target = await getPhoto(id);
+    if (seq !== openSeq) return;
+    let shown = false;
+    if (target.isPano && target.urls.pano && ensureRenderer()) {
+      try {
+        shown = await showPano(target, seq, keepView);
+      } catch {
+        // The panorama failed: its front view is better than nothing.
+        if (seq !== openSeq) return;
+        shown = await showFlat(target, seq);
+      }
+    } else shown = await showFlat(target, seq);
+    if (!shown) return;
+    emit();
+    onShown(target);
+    upgrade(target, seq, showing);
+  }
+
+  const adapter = {
+    async mount(host) {
+      if (!host) throw new Error('Street Level viewer has no host element');
+      if (root && root.parentNode === host) return;
+      teardown();
+      rendererFailed = false;
+      build(host);
+    },
+
+    /** Resolves once the photo is on screen and its pose was emitted. */
+    async open(imageId) {
+      if (!root) throw new Error('KartaView viewer is not mounted');
+      const id = String(imageId);
+      const seq = ++openSeq;
+      const keepView = keepViewFor === id;
+      keepViewFor = null;
+      openingId = id;
+      try {
+        await openPhoto(id, seq, keepView);
+      } finally {
+        if (openingId === id && seq === openSeq) openingId = null;
+      }
+    },
+
+    close() {
+      openSeq++;
+      openingId = null;
+      keepViewFor = null;
+      photo = null;
+      show(null);
+      if (picture) picture.removeAttribute('src');
+      renderer?.clear?.();
+    },
+
+    unmount() {
+      openSeq++;
+      openingId = null;
+      keepViewFor = null;
+      teardown();
+    },
+
+    resize() {
+      renderer?.resize();
+      // Expanded: a docked viewer's first version is now too soft.
+      if (showing === 'pano' && photo && panoSizeNow()[0] > panoWidth)
+        upgrade(photo, openSeq, 'pano');
+      if (showing === 'flat' && photo && !flatSharp)
+        upgrade(photo, openSeq, 'flat');
+    },
+
+    /** FIT / FILL frame a flat photo; a panorama has no frame to fit. */
+    supportsRenderModes: () => showing !== 'pano',
+
+    setRenderMode(mode) {
+      renderMode = mode === 'fill' ? 'fill' : 'letterbox';
+      applyRenderMode();
+    },
+
+    /** The photo's direction became known (its drive loaded): pose again. */
+    refreshPose() {
+      emit();
+    },
+
+    onPose(listener) {
+      listeners.add(listener);
+      return () => listeners.delete(listener);
+    },
+  };
+  return adapter;
+}

src/layers/streetLevel/providers/kartaview/viewer.test.mjs

@@ -0,0 +1,984 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { createKartaViewViewer, loadImage, panoSizeFor } from './viewer.js';
+import { fakeHost, until } from '../../../../testSupport/kartaViewFakes.mjs';
+
+const PHOTOS = {
+  flat1: {
+    id: 'flat1',
+    sequenceId: 's1',
+    sequenceIndex: 1,
+    lon: -83.04,
+    lat: 42.33,
+    heading: 90,
+    isPano: false,
+    capturedAt: Date.UTC(2016, 7, 23),
+    urls: {
+      view: 'https://storage2.openstreetcam.org/lth/a.jpg',
+      full: 'https://storage2.openstreetcam.org/proc/a.jpg',
+      pano: null,
+    },
+  },
+  flat2: {
+    id: 'flat2',
+    sequenceId: 's1',
+    sequenceIndex: 2,
+    lon: -83.0401,
+    lat: 42.33,
+    heading: 92,
+    isPano: false,
+    capturedAt: Date.UTC(2016, 7, 23),
+    urls: {
+      view: 'https://storage2.openstreetcam.org/lth/b.jpg',
+      full: 'https://storage2.openstreetcam.org/proc/b.jpg',
+      pano: null,
+    },
+  },
+  pano1: {
+    id: 'pano1',
+    sequenceId: 's2',
+    sequenceIndex: 7,
+    lon: 106.84,
+    lat: -6.19,
+    heading: 150,
+    isPano: true,
+    capturedAt: Date.UTC(2022, 2, 21),
+    urls: {
+      view: 'https://storage13.openstreetcam.org/lth/p.jpg',
+      full: 'https://storage13.openstreetcam.org/wrapped_proc/p.jpg',
+      pano: 'https://storage13.openstreetcam.org/wrapped_proc/p.jpg',
+    },
+  },
+  pano2: {
+    id: 'pano2',
+    sequenceId: 's2',
+    sequenceIndex: 8,
+    lon: 106.8401,
+    lat: -6.19,
+    heading: 152,
+    isPano: true,
+    capturedAt: Date.UTC(2022, 2, 21),
+    urls: {
+      view: 'https://storage13.openstreetcam.org/lth/q.jpg',
+      full: 'https://storage13.openstreetcam.org/wrapped_proc/q.jpg',
+      pano: 'https://storage13.openstreetcam.org/wrapped_proc/q.jpg',
+    },
+  },
+};
+
+function fakeRenderer(canvas) {
+  const view = { yaw: 0, pitch: 0, fov: 80 };
+  return {
+    canvas,
+    images: [],
+    hiddenAtSetImage: [],
+    setImage(image) {
+      this.images.push(image.src);
+      // A hidden canvas measures 0×0: sizing it then gives a 1×1 buffer.
+      this.hiddenAtSetImage.push(canvas?.hidden);
+    },
+    setView(next) {
+      Object.assign(view, next);
+    },
+    getView: () => ({ ...view }),
+    resize() {},
+    clear() {},
+    destroy() {
+      this.destroyed = true;
+    },
+  };
+}
+
+PHOTOS.pano2 = {
+  ...PHOTOS.pano1,
+  id: 'pano2',
+  sequenceIndex: 8,
+  urls: {
+    view: 'https://storage13.openstreetcam.org/lth/p2.jpg',
+    full: 'https://storage13.openstreetcam.org/wrapped_proc/p2.jpg',
+    pano: 'https://storage13.openstreetcam.org/wrapped_proc/p2.jpg',
+  },
+};
+
+function setup({
+  failLoads = [],
+  rendererThrows = false,
+  steps = {},
+  failSteps = false,
+  hold = () => false,
+} = {}) {
+  const loads = [];
+  const held = [];
+  const closed = [];
+  const renderers = [];
+  const stepped = [];
+  const asked = [];
+  const attempts = { renderer: 0 };
+  const viewer = createKartaViewViewer({
+    getPhoto: async (id) => {
+      if (!PHOTOS[id]) throw new Error('no such photo');
+      return PHOTOS[id];
+    },
+    step: async (photo, delta) => {
+      asked.push(`${photo.id}:${delta}`);
+      if (failSteps) throw new Error('KartaView did not answer in time');
+      return steps[`${photo.id}:${delta}`] ?? null;
+    },
+    // The core opens what ‹ › chose; here the adapter is opened directly.
+    onStep: (id) => {
+      stepped.push(id);
+      viewer.open(id).catch(() => {});
+    },
+    load: async (url, options) => {
+      loads.push({ url, crossOrigin: options?.crossOrigin });
+      if (failLoads.some((part) => url.includes(part)))
+        throw new Error('The KartaView photo could not be loaded');
+      // A decoded bitmap: close() frees it.
+      const image = { src: url, close: () => closed.push(url) };
+      if (!hold(url)) return image;
+      return new Promise((resolve) => held.push(() => resolve(image)));
+    },
+    createRenderer: (canvas) => {
+      attempts.renderer++;
+      if (rendererThrows) throw new Error('WebGL is unavailable');
+      const renderer = fakeRenderer(canvas);
+      renderers.push(renderer);
+      return renderer;
+    },
+  });
+  const poses = [];
+  viewer.onPose((pose) => poses.push(pose));
+  const host = fakeHost();
+  return {
+    viewer,
+    poses,
+    host,
+    loads,
+    renderers,
+    stepped,
+    asked,
+    attempts,
+    held,
+    closed,
+  };
+}
+
+const parts = (host) => {
+  const root = host.children[0];
+  const [picture, canvas, prev, next] = root.children;
+  return { root, picture, canvas, prev, next };
+};
+const settle = () => new Promise((resolve) => setTimeout(resolve, 0));
+
+test('a flat photo shows its 1280 px version, then the sharp one, with a pose facing its heading', async () => {
+  const { viewer, poses, host, loads } = setup({
+    steps: { 'flat1:1': 'flat2', 'flat1:-1': 'flat0' },
+  });
+  await viewer.mount(host);
+  const { picture, canvas, prev, next } = parts(host);
+  picture.clientWidth = 1600; // expanded: the sharp version is wanted
+  assert.equal(prev.disabled, true, 'nothing to step through yet');
+  await viewer.open('flat1');
+  assert.equal(picture.hidden, false);
+  assert.equal(canvas.hidden, true);
+  assert.equal(prev.disabled, false);
+  assert.equal(next.disabled, false);
+  const pose = poses.at(-1);
+  assert.deepEqual(
+    {
+      providerId: pose.providerId,
+      imageId: pose.imageId,
+      position: pose.position,
+      bearing: pose.bearing,
+      tilt: pose.tilt,
+      isPano: pose.isPano,
+      sequenceId: pose.sequenceId,
+      capturedAt: pose.capturedAt,
+      title: pose.title,
+    },
+    {
+      providerId: 'kartaview',
+      imageId: 'flat1',
+      position: { lon: -83.04, lat: 42.33 },
+      bearing: 90,
+      tilt: 0,
+      isPano: false,
+      sequenceId: 's1',
+      capturedAt: Date.UTC(2016, 7, 23),
+      title: null,
+    },
+  );
+  assert.match(pose.externalUrl, /^https:\/\/cdn\.kartaview\.org\/pr:sharp\//);
+  // The proxy's 1,280 px version first: KartaView's own can be 1.7 MB.
+  assert.match(
+    loads[0].url,
+    /^https:\/\/cdn\.kartaview\.org\/.*rs:fit:1280:1280/,
+  );
+  assert.equal(loads[0].crossOrigin, false, 'an <img> needs no CORS');
+  await settle();
+  assert.match(
+    loads[1].url,
+    /^https:\/\/cdn\.kartaview\.org\/.*rs:fit:2560:2560/,
+  );
+  assert.equal(picture.src, loads[1].url, 'upgraded to the sharp version');
+  assert.equal(viewer.supportsRenderModes(), true);
+  viewer.setRenderMode('fill');
+  assert.equal(picture.style.objectFit, 'cover');
+});
+
+test('a failing image proxy falls back to the photo on KartaView storage', async () => {
+  const { viewer, host, loads } = setup({ failLoads: ['cdn.kartaview.org'] });
+  await viewer.mount(host);
+  await viewer.open('flat1');
+  assert.equal(loads[1].url, PHOTOS.flat1.urls.view);
+  assert.equal(parts(host).picture.hidden, false);
+  assert.equal(parts(host).picture.src, PHOTOS.flat1.urls.view);
+});
+
+test('a 360° photo shows on the panorama, preview first; dragging turns the bearing', async () => {
+  const { viewer, poses, host, loads, renderers } = setup();
+  await viewer.mount(host);
+  await viewer.open('pano1');
+  const { picture, canvas } = parts(host);
+  assert.equal(canvas.hidden, false);
+  assert.equal(picture.hidden, true);
+  assert.match(loads[0].url, /rs:fit:1024:512/);
+  assert.equal(loads[0].crossOrigin, true, 'WebGL textures need CORS');
+  assert.equal(poses.at(-1).isPano, true);
+  assert.equal(poses.at(-1).bearing, 150);
+  assert.equal(viewer.supportsRenderModes(), false, 'no frame to fit');
+  await settle();
+  // Docked (400 px at 80°), 2,048 px is all it can show.
+  assert.match(renderers[0].images.at(-1), /rs:fit:2048:1024/);
+  // Drag left by a quarter of the width: the view turns right.
+  const frames = [];
+  globalThis.requestAnimationFrame = (callback) => {
+    frames.push(callback);
+    return frames.length;
+  };
+  try {
+    canvas.fire('pointerdown', {
+      button: 0,
+      pointerId: 1,
+      clientX: 200,
+      clientY: 100,
+    });
+    canvas.fire('pointermove', { pointerId: 1, clientX: 100, clientY: 100 });
+    canvas.fire('pointerup', { pointerId: 1 });
+    frames.forEach((callback) => callback());
+  } finally {
+    delete globalThis.requestAnimationFrame;
+  }
+  const turned = poses.at(-1).bearing;
+  assert.ok(turned > 150 && turned < 360, `bearing ${turned} turned right`);
+});
+
+test('without WebGL, or when the panorama fails, a 360° photo shows its front view', async () => {
+  const noGl = setup({ rendererThrows: true });
+  await noGl.viewer.mount(noGl.host);
+  await noGl.viewer.open('pano1');
+  assert.equal(parts(noGl.host).picture.hidden, false);
+  assert.equal(noGl.loads[0].url, PHOTOS.pano1.urls.view);
+  assert.equal(noGl.poses.at(-1).isPano, false);
+  await settle();
+  assert.equal(
+    noGl.loads.length,
+    1,
+    'the equirectangular image never replaces it',
+  );
+
+  const broken = setup({ failLoads: ['cdn.kartaview.org'] });
+  await broken.viewer.mount(broken.host);
+  await broken.viewer.open('pano1');
+  assert.equal(parts(broken.host).picture.hidden, false);
+  assert.equal(broken.poses.at(-1).imageId, 'pano1');
+});
+
+test('‹ › and the arrow keys step along the sequence; ends disable at once', async () => {
+  const { viewer, poses, host, stepped, asked } = setup({
+    steps: { 'flat1:1': 'flat2', 'flat2:-1': 'flat1' },
+  });
+  await viewer.mount(host);
+  await viewer.open('flat1');
+  const { root, prev, next } = parts(host);
+  assert.ok(
+    await until(() => prev.disabled),
+    'flat1 is the first photo: known up front',
+  );
+  assert.equal(next.disabled, false);
+  next.fire('click');
+  assert.ok(await until(() => poses.at(-1).imageId === 'flat2'));
+  assert.deepEqual(stepped, ['flat2'], 'the core is asked to open it');
+  assert.ok(await until(() => next.disabled), 'flat2 is the last photo');
+  assert.equal(prev.disabled, false);
+  // A modified arrow, then a plain → (at the end: it only asks). Presses run
+  // in turn, so once → has asked, a stepping ⌘← would have asked first.
+  const before = asked.length;
+  root.fire('keydown', { key: 'ArrowLeft', metaKey: true });
+  root.fire('keydown', { key: 'ArrowRight' });
+  assert.ok(await until(() => asked.length > before));
+  await settle();
+  assert.deepEqual(
+    asked.slice(before),
+    ['flat2:1'],
+    'modified arrows are not ours',
+  );
+  assert.equal(poses.at(-1).imageId, 'flat2');
+  root.fire('keydown', { key: 'ArrowLeft' });
+  assert.ok(await until(() => poses.at(-1).imageId === 'flat1'));
+});
+
+test('quick presses each step on from the photo the last one chose', async () => {
+  const chain = { 'flat1:1': 'flat2', 'flat2:1': 'pano1' };
+  const { viewer, host, stepped } = setup({
+    steps: chain,
+    rendererThrows: true,
+  });
+  await viewer.mount(host);
+  await viewer.open('flat1');
+  const { next } = parts(host);
+  next.fire('click');
+  next.fire('click');
+  assert.ok(await until(() => stepped.length === 2), `stepped ${stepped}`);
+  assert.deepEqual(stepped, ['flat2', 'pano1']);
+});
+
+test('a newer open wins; close hides the photo; unmount tears down the panorama', async () => {
+  const { viewer, poses, host, renderers } = setup();
+  await viewer.mount(host);
+  const first = viewer.open('pano1');
+  const second = viewer.open('flat1');
+  await Promise.all([first, second]);
+  assert.deepEqual(
+    poses.map((pose) => pose.imageId),
+    ['flat1'],
+    'the overtaken panorama never posed',
+  );
+  assert.equal(renderers.length, 0, 'nor built a WebGL context');
+  await viewer.open('pano1');
+  viewer.close();
+  const { picture, canvas, root } = parts(host);
+  assert.equal(canvas.hidden, true);
+  assert.equal(picture.hidden, true);
+  assert.equal(root.dataset.kind, '');
+  await assert.rejects(viewer.open('nope'), /no such photo/);
+  viewer.unmount();
+  assert.equal(host.children.length, 0);
+  assert.equal(renderers[0].destroyed, true);
+  await assert.rejects(viewer.open('flat1'), /not mounted/);
+});
+
+test('a panorama is put on screen before its image is sized into the canvas', async () => {
+  const { viewer, host, renderers } = setup();
+  await viewer.mount(host);
+  await viewer.open('flat1');
+  await viewer.open('pano1');
+  await settle();
+  assert.deepEqual(renderers[0].hiddenAtSetImage, [false, false]);
+});
+
+test('a step that gets no answer is not the end of the sequence', async () => {
+  const { viewer, host, poses, asked } = setup({ failSteps: true });
+  await viewer.mount(host);
+  await viewer.open('flat1');
+  const { next } = parts(host);
+  next.disabled = false;
+  // The ends check asked once already; the press asks again and fails.
+  const asks = () => asked.filter((ask) => ask === 'flat1:1').length;
+  next.fire('click');
+  assert.ok(await until(() => asks() === 2), 'the press asked');
+  await settle();
+  assert.equal(next.disabled, false, 'still enabled: try again');
+  assert.equal(poses.at(-1).imageId, 'flat1');
+});
+
+test('the keyboard looks around a panorama: Shift+arrows turn, ↑ ↓ tilt, + − zoom', async (t) => {
+  globalThis.requestAnimationFrame = (callback) => setTimeout(callback, 0);
+  t.after(() => delete globalThis.requestAnimationFrame);
+  const { viewer, host, renderers, stepped, asked } = setup({
+    steps: { 'pano1:1': 'flat1' },
+  });
+  await viewer.mount(host);
+  await viewer.open('pano1');
+  const { root } = parts(host);
+  const view = () => renderers[0].getView();
+  const before = asked.length;
+  root.fire('keydown', { key: 'ArrowRight', shiftKey: true });
+  assert.ok(view().yaw > 0, 'turned right');
+  root.fire('keydown', { key: 'ArrowUp' });
+  assert.ok(view().pitch > 0, 'looked up');
+  const fov = view().fov;
+  root.fire('keydown', { key: '+' });
+  assert.ok(view().fov < fov, 'zoomed in');
+  root.fire('keydown', { key: '-' });
+  root.fire('keydown', { key: '-' });
+  assert.ok(view().fov > fov, 'zoomed out');
+  root.fire('keydown', { key: 'ArrowRight' });
+  assert.ok(await until(() => stepped.length === 1));
+  assert.deepEqual(stepped, ['flat1'], 'a plain arrow still steps');
+  // Only that press asked, then flat1's ends check: a Shift+→ that stepped
+  // would have sent the plain → on from flat1.
+  assert.ok(await until(() => asked.slice(before).length >= 3));
+  await settle();
+  assert.deepEqual(
+    asked.slice(before).sort(),
+    ['flat1:-1', 'flat1:1', 'pano1:1'],
+    'none of the others stepped',
+  );
+});
+
+test('two fingers pinch the panorama’s zoom', async () => {
+  const { viewer, host, renderers } = setup();
+  await viewer.mount(host);
+  await viewer.open('pano1');
+  const { canvas } = parts(host);
+  const before = renderers[0].getView().fov;
+  canvas.fire('pointerdown', {
+    pointerId: 1,
+    pointerType: 'touch',
+    clientX: 100,
+    clientY: 100,
+  });
+  canvas.fire('pointerdown', {
+    pointerId: 2,
+    pointerType: 'touch',
+    clientX: 140,
+    clientY: 100,
+  });
+  canvas.fire('pointermove', {
+    pointerId: 2,
+    pointerType: 'touch',
+    clientX: 180,
+    clientY: 100,
+  });
+  assert.ok(renderers[0].getView().fov < before, 'spread zooms in');
+  canvas.fire('pointerup', { pointerId: 1 });
+  canvas.fire('pointerup', { pointerId: 2 });
+});
+
+test('a lost WebGL context drops the panorama and shows the photo again on a new one', async () => {
+  const { viewer, host, renderers, poses, stepped } = setup();
+  await viewer.mount(host);
+  await viewer.open('pano1');
+  const lost = parts(host).canvas;
+  lost.fire('webglcontextlost');
+  assert.equal(renderers[0].destroyed, true);
+  // A lost canvas only ever gives back its lost context: a new element.
+  assert.notEqual(parts(host).canvas, lost);
+  assert.deepEqual(stepped, ['pano1'], 'reopened through the core');
+  assert.ok(await until(() => renderers.length === 2), 'a new renderer');
+  assert.equal(renderers[1].canvas, parts(host).canvas);
+  assert.equal(poses.at(-1).imageId, 'pano1');
+  assert.equal(parts(host).canvas.hidden, false);
+});
+
+test('a context lost while a newer photo opens leaves that open alone', async () => {
+  const { viewer, host, stepped } = setup();
+  await viewer.mount(host);
+  await viewer.open('pano1');
+  const opening = viewer.open('flat1');
+  parts(host).canvas.fire('webglcontextlost');
+  await opening;
+  assert.deepEqual(stepped, [], 'no reopen of the old panorama');
+  assert.equal(parts(host).picture.hidden, false);
+});
+
+test('a WebGL failure only lasts until the viewer is mounted again', async () => {
+  let fail = true;
+  const built = [];
+  const viewer = createKartaViewViewer({
+    getPhoto: async (id) => PHOTOS[id],
+    step: async () => null,
+    onStep() {},
+    load: async (url) => ({ src: url }),
+    createRenderer: (canvas) => {
+      if (fail) throw new Error('WebGL is unavailable');
+      const renderer = fakeRenderer(canvas);
+      built.push(renderer);
+      return renderer;
+    },
+  });
+  const host = fakeHost();
+  await viewer.mount(host);
+  await viewer.open('pano1');
+  assert.equal(parts(host).picture.hidden, false, 'front view');
+  viewer.unmount();
+  fail = false;
+  const again = fakeHost();
+  await viewer.mount(again);
+  await viewer.open('pano1');
+  assert.equal(built.length, 1);
+  assert.equal(parts(again).canvas.hidden, false);
+});
+
+/** Flat photos a → d of one drive, for the tests that hold loads back. */
+const DRIVE = Object.fromEntries(
+  ['a', 'b', 'c', 'd'].map((id, index) => [
+    id,
+    {
+      id,
+      sequenceId: 'drive',
+      sequenceIndex: index,
+      lon: 0.1 + index * 0.0001,
+      lat: 0.1,
+      heading: 0,
+      isPano: false,
+      capturedAt: 0,
+      urls: {
+        view: `https://storage2.openstreetcam.org/lth/${id}.jpg`,
+        full: `https://storage2.openstreetcam.org/proc/${id}.jpg`,
+        pano: null,
+      },
+    },
+  ]),
+);
+const DRIVE_ORDER = Object.keys(DRIVE);
+
+/** Which drive photo, at which size, an image address shows. */
+function shows(src) {
+  const proxied =
+    /^https:\/\/cdn\.kartaview\.org\/pr:sharp\/rs:fit:(\d+):\d+\/([\w-]+)$/.exec(
+      src || '',
+    );
+  const url = proxied ? Buffer.from(proxied[2], 'base64url').toString() : src;
+  const id = /\/(\w+)\.jpg$/.exec(url || '')?.[1] ?? null;
+  return proxied ? `${id}@${proxied[1]}` : id;
+}
+
+/**
+ * A viewer whose photo loads (and, with `slowSteps`, step answers) wait for
+ * the test. ‹ › open through a stand-in core that, like the real one, awaits
+ * a tick (the viewer mount) before it opens the photo.
+ */
+function heldSetup({ slowSteps = false } = {}) {
+  const loads = [];
+  const asks = [];
+  const stepped = [];
+  const shown = [];
+  const viewer = createKartaViewViewer({
+    getPhoto: async (id) => {
+      if (!DRIVE[id]) throw new Error('no such photo');
+      return DRIVE[id];
+    },
+    step: (photo, delta) => {
+      const answer = DRIVE_ORDER[DRIVE_ORDER.indexOf(photo.id) + delta] ?? null;
+      if (!slowSteps) return Promise.resolve(answer);
+      return new Promise((resolve) =>
+        asks.push({ key: `${photo.id}:${delta}`, resolve }),
+      );
+    },
+    onStep: async (id) => {
+      stepped.push(id);
+      await settle();
+      viewer.open(id).catch(() => {});
+    },
+    onShown: (photo) => shown.push(photo.id),
+    load: (url) =>
+      new Promise((resolve, reject) =>
+        loads.push({
+          url,
+          shows: shows(url),
+          resolve: () => resolve({ src: url }),
+          reject: () =>
+            reject(new Error('The KartaView photo could not be loaded')),
+        }),
+      ),
+    createRenderer: () => {
+      throw new Error('no WebGL in Node');
+    },
+  });
+  const poses = [];
+  viewer.onPose((pose) => poses.push(pose.imageId));
+  const host = fakeHost();
+  /** Let the load showing `what` (e.g. 'a@1280') finish. */
+  const release = async (what) => {
+    assert.ok(
+      await until(() => loads.some((load) => load.shows === what)),
+      `${what} is loading: ${loads.map((load) => load.shows)}`,
+    );
+    const at = loads.findIndex((load) => load.shows === what);
+    loads.splice(at, 1)[0].resolve();
+    await settle();
+  };
+  /** Answer the oldest pending step ask for `key` (e.g. 'a:1'). */
+  const answer = async (key, value) => {
+    assert.ok(await until(() => asks.some((ask) => ask.key === key)));
+    const at = asks.findIndex((ask) => ask.key === key);
+    asks.splice(at, 1)[0].resolve(value);
+    await settle();
+  };
+  return { viewer, host, loads, asks, stepped, shown, poses, release, answer };
+}
+
+test('quick presses while the next photo is still loading each step on from the last one chosen', async () => {
+  const { viewer, host, stepped, release } = heldSetup();
+  await viewer.mount(host);
+  const opening = viewer.open('a');
+  await release('a@1280');
+  await opening;
+  const { next } = parts(host);
+  assert.ok(await until(() => !next.disabled));
+  // b, c and d never load: each press steps on from the photo on its way.
+  next.fire('click');
+  next.fire('click');
+  next.fire('click');
+  assert.ok(await until(() => stepped.length >= 3), `stepped ${stepped}`);
+  await settle();
+  assert.deepEqual(stepped, ['b', 'c', 'd']);
+});
+
+test('a slow sharp version of an older photo never replaces the newer photo', async () => {
+  const { viewer, host, shown, poses, release } = heldSetup();
+  await viewer.mount(host);
+  // An expanded viewer, so the sharp version is wanted.
+  parts(host).picture.clientWidth = 1600;
+  const first = viewer.open('a');
+  await release('a@1280');
+  await first;
+  const second = viewer.open('b');
+  await release('b@1280');
+  await second;
+  const { picture } = parts(host);
+  assert.equal(shows(picture.src), 'b@1280');
+  await release('a@2560'); // a's upgrade, overtaken
+  assert.equal(shows(picture.src), 'b@1280', 'a never comes back');
+  await release('b@2560');
+  assert.equal(shows(picture.src), 'b@2560', 'b’s own upgrade lands');
+  assert.deepEqual(shown, ['a', 'b']);
+  assert.deepEqual(poses, ['a', 'b']);
+});
+
+test('an overtaken flat open never shows, nor tells the provider it did', async () => {
+  const { viewer, host, shown, poses, loads, release } = heldSetup();
+  await viewer.mount(host);
+  const first = viewer.open('a');
+  assert.ok(await until(() => loads.length === 1), 'a is loading');
+  const second = viewer.open('b');
+  await release('b@1280');
+  await second;
+  await release('a@1280');
+  await first;
+  const { picture } = parts(host);
+  assert.equal(shows(picture.src), 'b@1280');
+  assert.deepEqual(poses, ['b']);
+  assert.deepEqual(shown, ['b'], 'onShown only for the photo on screen');
+});
+
+test('a photo still loading when the viewer closes stays closed', async () => {
+  const { viewer, host, shown, poses, loads, release } = heldSetup();
+  await viewer.mount(host);
+  const opening = viewer.open('a');
+  assert.ok(await until(() => loads.length === 1), 'a is loading');
+  viewer.close();
+  await release('a@1280');
+  await opening;
+  const { picture, root } = parts(host);
+  assert.equal(picture.hidden, true);
+  assert.equal(root.dataset.kind, '');
+  assert.deepEqual(poses, []);
+  assert.deepEqual(shown, []);
+});
+
+test('an ends check for an earlier photo does not disable › on the photo now showing', async () => {
+  const { viewer, host, release, answer } = heldSetup({ slowSteps: true });
+  await viewer.mount(host);
+  const first = viewer.open('a');
+  await release('a@1280');
+  await first;
+  const second = viewer.open('c');
+  await release('c@1280');
+  await second;
+  const { prev, next } = parts(host);
+  await answer('c:-1', 'b');
+  await answer('c:1', 'd');
+  // a's check answers last, saying nothing lies before or after it.
+  await answer('a:-1', null);
+  await answer('a:1', null);
+  assert.equal(prev.disabled, false);
+  assert.equal(next.disabled, false, 'c still has a next photo');
+});
+
+test('a press whose answer comes after another photo was opened is dropped', async () => {
+  const { viewer, host, stepped, release, answer, asks } = heldSetup({
+    slowSteps: true,
+  });
+  await viewer.mount(host);
+  const first = viewer.open('a');
+  await release('a@1280');
+  await first;
+  await answer('a:-1', null);
+  await answer('a:1', 'b');
+  const { next } = parts(host);
+  next.disabled = false;
+  next.fire('click');
+  assert.ok(await until(() => asks.some((ask) => ask.key === 'a:1')));
+  // The user picks another photo meanwhile.
+  const other = viewer.open('d');
+  await release('d@1280');
+  await other;
+  await answer('a:1', 'b');
+  await settle();
+  assert.deepEqual(stepped, [], 'the old press does not open b over d');
+});
+
+test('a failed open does not become the photo ‹ › step from', async () => {
+  const { viewer, host, stepped } = setup({ steps: { 'flat1:1': 'flat2' } });
+  await viewer.mount(host);
+  await viewer.open('flat1');
+  await assert.rejects(viewer.open('nope'), /no such photo/);
+  parts(host).next.disabled = false;
+  parts(host).next.fire('click');
+  assert.ok(await until(() => stepped.length === 1));
+  assert.deepEqual(stepped, ['flat2'], 'from the photo still showing');
+});
+
+test('WebGL is tried once per mount, not again for every 360° photo', async () => {
+  const { viewer, host, attempts } = setup({ rendererThrows: true });
+  await viewer.mount(host);
+  await viewer.open('pano1');
+  await viewer.open('pano2');
+  assert.equal(attempts.renderer, 1);
+  assert.equal(parts(host).picture.hidden, false, 'front views instead');
+});
+
+test('a step button that disables under the keyboard hands focus to the viewer', async () => {
+  const { viewer, host } = setup();
+  await viewer.mount(host);
+  const { root, prev, next } = parts(host);
+  let focused = 0;
+  root.focus = () => focused++;
+  next.ownerDocument = { activeElement: next };
+  prev.ownerDocument = { activeElement: root };
+  await viewer.open('flat1');
+  assert.ok(await until(() => next.disabled && prev.disabled));
+  assert.equal(focused, 1, 'only for the focused button');
+});
+
+test('› to another 360° photo keeps the look direction; opening one afresh faces its heading', async (t) => {
+  globalThis.requestAnimationFrame = (callback) => setTimeout(callback, 0);
+  t.after(() => delete globalThis.requestAnimationFrame);
+  const { viewer, host, renderers, poses } = setup({
+    steps: { 'pano1:1': 'pano2' },
+  });
+  await viewer.mount(host);
+  await viewer.open('pano1');
+  const { root, next } = parts(host);
+  root.fire('keydown', { key: 'ArrowRight', shiftKey: true });
+  const yaw = renderers[0].getView().yaw;
+  assert.ok(yaw > 0);
+  next.fire('click');
+  assert.ok(await until(() => poses.at(-1).imageId === 'pano2'));
+  assert.equal(renderers[0].getView().yaw, yaw, 'still looking the same way');
+  await viewer.open('pano1');
+  assert.equal(renderers[0].getView().yaw, 0, 'a fresh open faces ahead');
+});
+
+/** A viewer whose loads for `held` URLs wait until `release()`. */
+function heldPanoSetup(held) {
+  const renderers = [];
+  const stepped = [];
+  let release;
+  const gate = new Promise((resolve) => (release = resolve));
+  const viewer = createKartaViewViewer({
+    getPhoto: async (id) => PHOTOS[id],
+    step: async () => null,
+    onStep: (id) => {
+      stepped.push(id);
+      viewer.open(id).catch(() => {});
+    },
+    load: async (url) => {
+      if (held.some((part) => url.includes(part))) await gate;
+      return { src: url };
+    },
+    createRenderer: (canvas) => {
+      const renderer = fakeRenderer(canvas);
+      renderers.push(renderer);
+      return renderer;
+    },
+  });
+  const poses = [];
+  viewer.onPose((pose) => poses.push(pose));
+  return { viewer, renderers, stepped, poses, host: fakeHost(), release };
+}
+
+const pano2Preview = Buffer.from(
+  'https://storage13.openstreetcam.org/wrapped_proc/p2.jpg',
+).toString('base64url');
+
+test('a context lost while a newer panorama loads shows that one on a new canvas, not a black viewer', async () => {
+  const { viewer, renderers, poses, host, release, stepped } = heldPanoSetup([
+    pano2Preview,
+  ]);
+  await viewer.mount(host);
+  await viewer.open('pano1');
+  const opening = viewer.open('pano2');
+  await new Promise((resolve) => setTimeout(resolve, 0));
+  parts(host).canvas.fire('webglcontextlost');
+  release();
+  await opening;
+  assert.equal(
+    poses.at(-1).imageId,
+    'pano2',
+    'the newer panorama is on screen',
+  );
+  assert.equal(poses.at(-1).isPano, true);
+  assert.deepEqual(stepped, [], 'its own open, not a reopen of the old one');
+  assert.equal(renderers.length, 2, 'drawn by a new renderer');
+  assert.equal(renderers[1].canvas, parts(host).canvas);
+  assert.equal(parts(host).canvas.hidden, false);
+});
+
+test('a second context loss, on the new canvas, reopens again; the new canvas still drags', async (t) => {
+  globalThis.requestAnimationFrame = (callback) => setTimeout(callback, 0);
+  t.after(() => delete globalThis.requestAnimationFrame);
+  const { viewer, host, renderers, stepped, poses } = setup();
+  await viewer.mount(host);
+  await viewer.open('pano1');
+  parts(host).canvas.fire('webglcontextlost');
+  assert.ok(await until(() => renderers.length === 2));
+  parts(host).canvas.fire('webglcontextlost');
+  assert.ok(await until(() => renderers.length === 3), 'reopened twice');
+  assert.deepEqual(stepped, ['pano1', 'pano1']);
+  assert.equal(renderers[2].canvas, parts(host).canvas);
+  const canvas = parts(host).canvas;
+  const before = poses.at(-1).bearing;
+  canvas.fire('pointerdown', {
+    button: 0,
+    pointerId: 7,
+    pointerType: 'mouse',
+    clientX: 200,
+    clientY: 100,
+  });
+  canvas.fire('pointermove', { pointerId: 7, clientX: 100, clientY: 100 });
+  canvas.fire('pointerup', { pointerId: 7 });
+  assert.ok(await until(() => poses.at(-1).bearing !== before), 'dragged');
+});
+
+test('a context loss keeps where the user was looking', async () => {
+  const { viewer, host, renderers } = setup();
+  await viewer.mount(host);
+  await viewer.open('pano1');
+  renderers[0].setView({ yaw: 70, pitch: 12, fov: 60 });
+  parts(host).canvas.fire('webglcontextlost');
+  assert.ok(await until(() => renderers.length === 2));
+  assert.deepEqual(renderers[1].getView(), { yaw: 70, pitch: 12, fov: 60 });
+});
+
+test('the panorama is as sharp as the viewer needs: 2,048 docked, 4,096 once expanded', async () => {
+  assert.deepEqual(panoSizeFor(400, 80), [2048, 1024]);
+  assert.deepEqual(panoSizeFor(1400, 80), [4096, 2048]);
+  const { viewer, host, renderers } = setup();
+  await viewer.mount(host);
+  await viewer.open('pano1');
+  assert.ok(await until(() => renderers[0].images.length === 2));
+  assert.match(renderers[0].images[1], /rs:fit:2048:1024/);
+  // Expanded: the panel tells the viewer it resized.
+  parts(host).canvas.clientWidth = 1400;
+  viewer.resize();
+  assert.ok(await until(() => renderers[0].images.length === 3));
+  assert.match(renderers[0].images[2], /rs:fit:4096:2048/);
+  viewer.resize();
+  for (let i = 0; i < 4; i++) await new Promise((r) => setTimeout(r, 0));
+  assert.equal(renderers[0].images.length, 3, 'not again once sharp');
+});
+
+test('a CORS image is decoded off the main thread into an ImageBitmap where the browser can', async (t) => {
+  const saved = {
+    fetch: globalThis.fetch,
+    bitmap: globalThis.createImageBitmap,
+  };
+  t.after(() => {
+    globalThis.fetch = saved.fetch;
+    globalThis.createImageBitmap = saved.bitmap;
+  });
+  const fetched = [];
+  globalThis.fetch = async (url, init) => {
+    fetched.push({ url, mode: init.mode });
+    return url.includes('gone')
+      ? { ok: false, status: 409 }
+      : { ok: true, blob: async () => 'blob' };
+  };
+  globalThis.createImageBitmap = async (blob) => ({
+    blob,
+    width: 4096,
+    height: 2048,
+  });
+  const bitmap = await loadImage('https://cdn.kartaview.org/a', {
+    crossOrigin: true,
+  });
+  assert.deepEqual(bitmap, { blob: 'blob', width: 4096, height: 2048 });
+  assert.deepEqual(fetched, [
+    { url: 'https://cdn.kartaview.org/a', mode: 'cors' },
+  ]);
+  await assert.rejects(
+    loadImage('https://cdn.kartaview.org/gone', { crossOrigin: true }),
+    /could not be loaded/,
+  );
+});
+
+test('a docked viewer keeps the 1,280 px photo; expanding it brings the 2,560 px one', async () => {
+  const { viewer, host, loads } = setup();
+  await viewer.mount(host);
+  await viewer.open('flat1');
+  for (let i = 0; i < 4; i++) await settle();
+  assert.equal(loads.length, 1, 'no 2,560 px download for a 400 px frame');
+  parts(host).picture.clientWidth = 1600;
+  viewer.resize();
+  assert.ok(await until(() => loads.length === 2));
+  assert.match(loads[1].url, /rs:fit:2560:2560/);
+  assert.equal(parts(host).picture.src, loads[1].url);
+  viewer.resize();
+  for (let i = 0; i < 4; i++) await settle();
+  assert.equal(loads.length, 2, 'once only');
+});
+
+test('resizes while a sharper panorama loads start no second load; the last size wins once it lands', async () => {
+  let first = true;
+  const { viewer, host, loads, renderers, held } = setup({
+    hold: (url) => {
+      const holdIt = first && url.includes('rs:fit:2048');
+      if (holdIt) first = false;
+      return holdIt;
+    },
+  });
+  await viewer.mount(host);
+  await viewer.open('pano1');
+  assert.ok(await until(() => held.length === 1));
+  // The panel animates open: a burst of resizes while 2,048 px loads.
+  parts(host).canvas.clientWidth = 1400;
+  for (let i = 0; i < 5; i++) viewer.resize();
+  for (let i = 0; i < 4; i++) await settle();
+  assert.equal(loads.length, 2, 'the preview and the one 2,048 px load');
+  held[0]();
+  assert.ok(await until(() => renderers[0].images.length === 3));
+  assert.match(renderers[0].images[1], /rs:fit:2048:1024/);
+  assert.match(renderers[0].images[2], /rs:fit:4096:2048/);
+  for (let i = 0; i < 4; i++) await settle();
+  assert.equal(loads.length, 3, 'one more load, for the size asked last');
+});
+
+test('a preview or sharper version nobody will draw is freed, not left decoded', async () => {
+  const { viewer, host, renderers, held, closed } = setup({
+    hold: (url) => /rs:fit:(1024|2048):/.test(url),
+  });
+  await viewer.mount(host);
+  // pano1's preview is still loading when flat1 opens over it.
+  const overtaken = viewer.open('pano1');
+  assert.ok(await until(() => held.length === 1));
+  await viewer.open('flat1');
+  held[0]();
+  await overtaken;
+  assert.deepEqual(closed.length, 1);
+  assert.match(closed[0], /rs:fit:1024/, 'the overtaken preview');
+  // pano1 shows; its sharp version lands after flat1 replaced it.
+  const shown = viewer.open('pano1');
+  assert.ok(await until(() => held.length === 2));
+  held[1]();
+  await shown;
+  assert.ok(await until(() => held.length === 3));
+  await viewer.open('flat1');
+  held[2]();
+  assert.ok(await until(() => closed.length === 2));
+  assert.match(closed[1], /rs:fit:2048/, 'the overtaken sharp version');
+  assert.equal(renderers[0].images.length, 1, 'only the preview was drawn');
+});

src/layers/streetLevel/providers/mapillary/coverage.js

@@ -1,21 +1,11 @@
-import * as Cesium from 'cesium';
-import { decodeCoverageTile } from './decode.js';
-import { passesImageryFilter } from '../../filter.js';
 import {
-  createHorizonCull,
-  groundUnderCamera,
-  metresBetween,
-  viewFocus,
-  visibleBbox,
-  whenIdle,
-} from '../../view.js';
-import { densifyLine, MESH_DENSIFY_DEG } from '../../groundCast.js';
-import { MESH_SAMPLE_RADIUS_M } from '../../meshSampler.js';
+  createLineCoverage,
+  sequenceIdFromPick as lineSequenceIdFromPick,
+} from '../../lineCoverage.js';
+import { decodeCoverageTile } from './decode.js';
 import {
   coverageZoomForHeight,
   overviewZoomForHeight,
-  tileBounds,
-  tilesForBbox,
 } from '../../tileMath.js';
 import {
   COLORS,
@@ -33,885 +23,48 @@ import {
   SEQUENCE_VIEW_RANGE_PER_HEIGHT,
 } from './policy.js';
 
-/** Draped lines stay at most this long while a tile's cast lines build. */
-export const SWAP_MAX_WAIT_MS = 4000;
-/** Tiles touched by new mesh samples are redrawn at most this often. */
-const REMESH_INTERVAL_MS = 1500;
-/** Gap between redrawing one dirty tile and the next. */
-const REMESH_STAGGER_MS = 120;
-/** Old-zoom tiles are kept at most this long after a zoom change. */
-const STALE_TILE_MAX_MS = 6000;
-/** Sequences per primitive: smaller batches build, and show, sooner. */
-const SEQUENCE_PRIMITIVE_BATCH = 120;
+export { SWAP_MAX_WAIT_MS, meshBoxInRange } from '../../lineCoverage.js';
 
-const PER_TILE_SEQUENCE_CAP = Math.floor(
-  COVERAGE_MAX_SEQUENCES / COVERAGE_MAX_TILES,
-);
-
-/** Colour for a sequence: Mapillary green, GEV cyan while selected. */
-function sequenceColor({ selected = false } = {}) {
-  return selected
-    ? Cesium.Color.fromCssColorString(COLORS.selected)
-    : Cesium.Color.fromCssColorString(COLORS.coverage).withAlpha(0.92);
-}
-
-/** Separates a multi-part sequence's part index from its id in pick ids. */
-const PART_SEPARATOR = '~';
-
-/** Pick ids for every part of a sequence; the first part is unsuffixed. */
-function partIds(sequence) {
-  return sequence.parts.map((_, index) =>
-    index
-      ? `${PICK_PREFIX.sequence}${sequence.id}${PART_SEPARATOR}${index}`
-      : `${PICK_PREFIX.sequence}${sequence.id}`,
-  );
+/** Overview points (z0–5) from orbit, sequence lines (z11–14) below 60 km. */
+export function mapillaryZoomFor(heightM) {
+  const sequence = coverageZoomForHeight(heightM);
+  if (sequence != null) return { zoom: sequence, kind: 'sequence' };
+  const overview = overviewZoomForHeight(heightM);
+  return overview != null ? { zoom: overview, kind: 'overview' } : null;
 }
 
 /** Sequence id for any part's pick id (`mly:seq:<id>[~<part>]`), else null. */
 export function sequenceIdFromPick(pickId) {
-  if (typeof pickId !== 'string' || !pickId.startsWith(PICK_PREFIX.sequence))
-    return null;
-  const rest = pickId.slice(PICK_PREFIX.sequence.length);
-  const cut = rest.indexOf(PART_SEPARATOR);
-  return cut === -1 ? rest : rest.slice(0, cut);
+  return lineSequenceIdFromPick(pickId, PICK_PREFIX.sequence);
 }
 
-/**
- * Whether any point of `box` ({west, south, east, north}) is within the mesh
- * sampler's range of `centre`, the ground point under the camera.
- */
-export function meshBoxInRange(box, centre) {
-  // Move the camera's longitude to the box's side of the date line first:
-  // clamping 179.999 into a box at -179.99 would pick its far edge.
-  const lon =
-    centre.lon +
-    360 * Math.round(((box.west + box.east) / 2 - centre.lon) / 360);
-  const nearest = {
-    lon: Math.min(box.east, Math.max(box.west, lon)),
-    lat: Math.min(box.north, Math.max(box.south, centre.lat)),
-  };
-  return metresBetween(centre, nearest) <= MESH_SAMPLE_RADIUS_M;
-}
-
-/**
- * Camera-driven coverage: overview points (z0–5) from orbit, sequence lines
- * (z11–14) near the ground. In terrain surface mode a tile is drawn draped
- * first, then swapped for lines cast to the bare earth (draped lines would
- * land on roofs), so coverage never waits on terrain heights.
- */
+/** Mapillary's vector-tile coverage through the server proxy. */
 export function createCoverage({ state, source }) {
-  const { render } = state.services;
-
-  function requestRender() {
-    render?.governorRequestRender?.('mapillary-coverage');
-  }
-
-  function ensureTerrainReady() {
-    return (state.coverage.terrainReady ||=
-      Cesium.GroundPolylinePrimitive.initializeTerrainHeights());
-  }
-
-  function tileKey({ x, y, z }) {
-    return `${z}/${x}/${y}`;
-  }
-
-  /** The imagery filter, resolved now: "since N days" moves with the clock. */
-  function filter() {
-    return state.context.getFilter();
-  }
-
-  function terrainMode() {
-    return (
-      state.context.getSurface?.() === 'terrain' &&
-      Boolean(state.context.groundCaster)
-    );
-  }
-
-  /**
-   * A tile's sequences, filtered then capped: capping first could leave a
-   * dense tile of newer flat captures with no 360° lines at all.
-   */
-  function drawnSequences(entry) {
-    const drawn = [];
-    const current = filter();
-    for (const sequence of entry.sequenceList) {
-      if (drawn.length >= PER_TILE_SEQUENCE_CAP) break;
-      if (passesImageryFilter(sequence, current)) drawn.push(sequence);
-    }
-    return drawn;
-  }
-
-  /**
-   * Batched primitives for a tile's sequence parts: cast polylines where
-   * terrain heights are cached, draped ground lines otherwise. Each batch
-   * records the selection its colours were built with.
-   */
-  function buildSequencePrimitives(sequences) {
-    const ground = terrainMode() ? state.context.groundCaster : null;
-    const meshAt = ground ? state.context.meshSampler?.meshAt : undefined;
-    const selectedId = state.sequence.selectedId ?? null;
-    const draped = [];
-    const cast = [];
-    for (const sequence of sequences) {
-      const color = Cesium.ColorGeometryInstanceAttribute.fromColor(
-        sequenceColor({ selected: sequence.id === selectedId }),
-      );
-      const ids = partIds(sequence);
-      sequence.parts.forEach((coordinates, index) => {
-        const flat = ground?.castLine(coordinates, { meshAt });
-        let positions;
-        try {
-          positions = flat
-            ? Cesium.Cartesian3.fromDegreesArrayHeights(flat)
-            : Cesium.Cartesian3.fromDegreesArray(coordinates.flat());
-        } catch {
-          return;
-        }
-        if (positions.length < 2) return;
-        const geometry = flat
-          ? new Cesium.PolylineGeometry({
-              positions,
-              width: COVERAGE_LINE_WIDTH_PX,
-              vertexFormat: Cesium.PolylineColorAppearance.VERTEX_FORMAT,
-              arcType: Cesium.ArcType.NONE,
-            })
-          : new Cesium.GroundPolylineGeometry({
-              positions,
-              width: COVERAGE_LINE_WIDTH_PX,
-            });
-        (flat ? cast : draped).push(
-          new Cesium.GeometryInstance({
-            geometry,
-            id: ids[index],
-            attributes: { color },
-          }),
-        );
-      });
-    }
-    const primitives = [];
-    for (let i = 0; i < draped.length; i += SEQUENCE_PRIMITIVE_BATCH)
-      primitives.push({
-        onGround: true,
-        selectedId,
-        primitive: new Cesium.GroundPolylinePrimitive({
-          geometryInstances: draped.slice(i, i + SEQUENCE_PRIMITIVE_BATCH),
-          appearance: new Cesium.PolylineColorAppearance(),
-          classificationType: Cesium.ClassificationType.BOTH,
-          asynchronous: true,
-          allowPicking: true,
-        }),
-      });
-    for (let i = 0; i < cast.length; i += SEQUENCE_PRIMITIVE_BATCH)
-      primitives.push({
-        onGround: false,
-        selectedId,
-        primitive: new Cesium.Primitive({
-          geometryInstances: cast.slice(i, i + SEQUENCE_PRIMITIVE_BATCH),
-          appearance: new Cesium.PolylineColorAppearance({ translucent: true }),
-          asynchronous: true,
-          allowPicking: true,
-        }),
-      });
-    return { primitives, draped, cast: cast.length };
-  }
-
-  /**
-   * Fetch the terrain heights a tile's lines need, then redraw it cast.
-   * `castRequested` stops the redraw from casting again at once; a refresh
-   * `retry`s a tile whose lines are still draped (a failed or partial cast),
-   * and it is redrawn only when more of its lines can be cast.
-   */
-  function castTile(entry, { retry = false } = {}) {
-    if ((entry.castRequested && !retry) || entry.castAbort || !terrainMode())
-      return;
-    entry.castRequested = true;
-    entry.castAbort = new AbortController();
-    const { signal } = entry.castAbort;
-    const lines = [...entry.sequences.values()].flatMap(
-      (sequence) => sequence.parts,
-    );
-    const caster = state.context.groundCaster;
-    caster.prepareLines(lines, { signal }).then(() => {
-      if (entry.castAbort?.signal === signal) entry.castAbort = null;
-      const attached = [...state.coverage.tiles.values()].includes(entry);
-      if (signal.aborted || !attached || !terrainMode()) return;
-      // Nothing new to cast: keep what is drawn until the next refresh.
-      // Counted like buildSequencePrimitives: a cast line needs two points.
-      const castable = lines.filter(
-        (coords) => caster.castLine(coords)?.length >= 6,
-      ).length;
-      if (castable <= (entry.castLines || 0)) {
-        entry.castRequested = (entry.castLines || 0) > 0;
-        return;
-      }
-      // A remesh may have cleared the flag while this was in flight.
-      entry.castRequested = true;
-      redrawTile(entry);
-      requestMesh(entry);
-    });
-  }
-
-  /** Rebuild a tile's lines; the old ones stay up until the new are ready. */
-  function redrawTile(entry) {
-    const previous = entry.primitives;
-    entry.primitives = [];
-    attachPrimitive(entry);
-    removeWhenReady(entry, previous);
-  }
-
-  /** Lon/lat under the camera, where mesh range is measured from. */
-  function meshCentre() {
-    const carto = state.viewer?.camera?.positionCartographic;
-    if (!carto) return null;
-    return {
-      lon: Cesium.Math.toDegrees(carto.longitude),
-      lat: Cesium.Math.toDegrees(carto.latitude),
-    };
-  }
-
-  /**
-   * A tile's drawn lines with bounding boxes, built once per filter; mesh
-   * points are densified the first time a line is in range.
-   */
-  function meshParts(entry) {
-    if (entry.meshParts) return entry.meshParts;
-    entry.meshParts = [];
-    for (const sequence of entry.sequences.values())
-      for (const part of sequence.parts) {
-        const box = {
-          west: Infinity,
-          south: Infinity,
-          east: -Infinity,
-          north: -Infinity,
-        };
-        for (const [lon, lat] of part) {
-          if (lon < box.west) box.west = lon;
-          if (lon > box.east) box.east = lon;
-          if (lat < box.south) box.south = lat;
-          if (lat > box.north) box.north = lat;
-        }
-        entry.meshParts.push({ part, box, points: null });
-      }
-    return entry.meshParts;
-  }
-
-  /**
-   * Ask for mesh samples under a cast tile's lines within the sampler's range
-   * of the camera; the rest are asked for when a camera move brings them in.
-   */
-  function requestMesh(entry) {
-    const sampler = state.context.meshSampler;
-    if (!sampler || entry.kind !== 'sequence' || !terrainMode()) return;
-    const centre = meshCentre();
-    if (!centre || !entry.bounds || !meshBoxInRange(entry.bounds, centre))
-      return;
-    const points = [];
-    for (const line of meshParts(entry)) {
-      if (!meshBoxInRange(line.box, centre)) continue;
-      line.points ||= densifyLine(line.part, MESH_DENSIFY_DEG);
-      for (const point of line.points) points.push(point);
-    }
-    if (points.length) sampler.request(points);
-  }
-
-  /** Redraw the tiles new mesh samples fall in, throttled. */
-  function onMeshSampled(batch) {
-    if (!terrainMode() || !state.context.isActive()) return;
-    for (const entry of state.coverage.tiles.values()) {
-      if (entry.kind !== 'sequence' || !entry.bounds) continue;
-      const { west, south, east, north } = entry.bounds;
-      if (
-        batch.some(
-          ([lon, lat]) =>
-            lon >= west && lon <= east && lat >= south && lat <= north,
-        )
-      )
-        state.coverage.remeshDirty.add(entry);
-    }
-    if (!state.coverage.remeshDirty.size || state.coverage.remeshTimer) return;
-    const wait = Math.max(
-      0,
-      REMESH_INTERVAL_MS - (Date.now() - (state.coverage.remeshAt || 0)),
-    );
-    state.coverage.remeshTimer = setTimeout(remesh, wait);
-  }
-
-  /** Redraw one dirty tile per idle slice, so a burst of samples never stalls a frame. */
-  function remesh() {
-    state.coverage.remeshTimer = null;
-    state.coverage.remeshAt = Date.now();
-    if (!terrainMode() || !state.context.isActive()) {
-      state.coverage.remeshDirty.clear();
-      return;
-    }
-    const attached = new Set(state.coverage.tiles.values());
-    const [entry] = state.coverage.remeshDirty;
-    if (!entry) return;
-    state.coverage.remeshDirty.delete(entry);
-    if (attached.has(entry)) {
-      redrawTile(entry);
-      requestRender();
-    }
-    if (state.coverage.remeshDirty.size)
-      state.coverage.remeshTimer = setTimeout(
-        () => whenIdle(remesh, 500),
-        REMESH_STAGGER_MS,
-      );
-  }
-
-  state.coverage.remeshDirty = new Set();
-  state.context.meshSampler?.onSampled(onMeshSampled);
-
-  /**
-   * Remove a tile's previous primitives once all its current ones are ready
-   * (or after a few seconds); detaching the tile removes them at once.
-   */
-  function removeWhenReady(entry, old) {
-    const scene = state.viewer?.scene;
-    finishSwap(entry);
-    if (!scene?.postRender) {
-      removePrimitives(old);
-      return;
-    }
-    const fresh = entry.primitives;
-    const started = Date.now();
-    const stop = scene.postRender.addEventListener(() => {
-      const ready = fresh.every(
-        ({ primitive }) => primitive.ready || primitive.isDestroyed?.(),
-      );
-      if (!ready && Date.now() - started < SWAP_MAX_WAIT_MS) {
-        requestRender();
-        return;
-      }
-      finishSwap(entry);
-      requestRender();
-    });
-    entry.swap = { old, stop };
-    requestRender();
-  }
-
-  function finishSwap(entry) {
-    if (!entry.swap) return;
-    entry.swap.stop();
-    removePrimitives(entry.swap.old);
-    entry.swap = null;
-  }
-
-  function buildOverviewCollection(points) {
-    const collection = new Cesium.PointPrimitiveCollection({
-      blendOption: Cesium.BlendOption.TRANSLUCENT,
-    });
-    const green = Cesium.Color.fromCssColorString(COLORS.coverage).withAlpha(
-      0.85,
-    );
-    const drawn = [];
-    const current = filter();
-    for (const point of points) {
-      if (!passesImageryFilter(point, current)) continue;
-      drawn.push(
-        collection.add({
-          position: Cesium.Cartesian3.fromDegrees(point.lon, point.lat),
-          color: green,
-          pixelSize: COVERAGE_OVERVIEW_POINT_PX,
-          // Google 3D terrain and clouds must not hide the near side's dots;
-          // the horizon cull hides the far side's, which this lets through.
-          disableDepthTestDistance: Number.POSITIVE_INFINITY,
-        }),
-      );
-    }
-    return { collection, points: drawn };
-  }
-
-  /** Every overview point on the globe, current zoom and old alike. */
-  function* overviewPoints() {
-    for (const entry of drawnEntries())
-      if (entry.overviewPoints) yield* entry.overviewPoints;
-  }
-
-  // Overview points skip the depth test: hide the far hemisphere's.
-  const horizon = createHorizonCull({
-    getViewer: () => state.viewer,
-    items: overviewPoints,
-    onChange: requestRender,
+  return createLineCoverage({
+    state,
+    fetchTile: async (tile, { signal }) =>
+      decodeCoverageTile(
+        await source.getTile('coverage', tile.z, tile.x, tile.y, { signal }),
+        tile,
+      ),
+    zoomFor: mapillaryZoomFor,
+    colors: COLORS,
+    pickPrefix: PICK_PREFIX.sequence,
+    renderKey: 'mapillary-coverage',
+    tuning: {
+      maxTiles: COVERAGE_MAX_TILES,
+      overviewMaxTiles: COVERAGE_OVERVIEW_MAX_TILES,
+      maxSequences: COVERAGE_MAX_SEQUENCES,
+      lineWidthPx: COVERAGE_LINE_WIDTH_PX,
+      overviewPointPx: COVERAGE_OVERVIEW_POINT_PX,
+      moveDebounceMs: COVERAGE_MOVE_DEBOUNCE_MS,
+      viewRangeMinM: SEQUENCE_VIEW_RANGE_MIN_M,
+      viewRangePerHeight: SEQUENCE_VIEW_RANGE_PER_HEIGHT,
+      viewNearM: SEQUENCE_VIEW_NEAR_M,
+    },
+    messages: {
+      keyRejected: KEY_REJECTED_MESSAGE,
+      rateLimited: RATE_LIMITED_MESSAGE,
+    },
   });
-
-  function attachPrimitive(entry) {
-    const scene = state.viewer?.scene;
-    if (!scene) return;
-    if (entry.kind === 'sequence') {
-      // Lookup, picking and counts follow what is drawn, not the whole tile.
-      const sequences = drawnSequences(entry);
-      entry.sequences = new Map(sequences.map((s) => [s.id, s]));
-      const { primitives, draped, cast } = buildSequencePrimitives(sequences);
-      entry.primitives = primitives;
-      entry.count = sequences.length;
-      for (const { primitive, onGround } of primitives)
-        (onGround ? scene.groundPrimitives : scene.primitives).add(primitive);
-      // Fewer lines cast than last time: the caster has dropped heights this
-      // tile used (a full cache), so it must be cast again.
-      if (cast < (entry.castLines || 0)) entry.castRequested = false;
-      entry.castLines = cast;
-      entry.drapedLines = draped.length;
-      if (draped.length) castTile(entry);
-      watchSelection();
-    } else {
-      const { collection, points } = buildOverviewCollection(entry.points);
-      entry.primitive = collection;
-      entry.overviewPoints = points;
-      entry.count = points.length;
-      scene.primitives.add(collection);
-      // Cull the new points now, then all of them whenever the camera moves.
-      horizon.update(points);
-    }
-  }
-
-  function removePrimitives(list) {
-    const scene = state.viewer?.scene;
-    for (const { primitive, onGround } of list || []) {
-      try {
-        (onGround ? scene?.groundPrimitives : scene?.primitives)?.remove(
-          primitive,
-        );
-      } catch {
-        /* already gone */
-      }
-    }
-  }
-
-  function detachPrimitive(entry) {
-    const scene = state.viewer?.scene;
-    finishSwap(entry);
-    removePrimitives(entry.primitives);
-    entry.primitives = [];
-    if (entry.primitive) {
-      try {
-        scene?.primitives?.remove(entry.primitive);
-      } catch {
-        /* already gone */
-      }
-      entry.primitive = null;
-      entry.overviewPoints = null;
-    }
-  }
-
-  /** Stop a tile's pending terrain lookup (tile dropped or retired). */
-  function cancelCast(entry) {
-    entry.castAbort?.abort();
-    entry.castAbort = null;
-  }
-
-  function removeTile(key) {
-    const entry = state.coverage.tiles.get(key);
-    if (!entry) return;
-    cancelCast(entry);
-    detachPrimitive(entry);
-    state.coverage.tiles.delete(key);
-  }
-
-  async function loadTile(tile, kind) {
-    const key = tileKey(tile);
-    if (state.coverage.tiles.has(key) || state.coverage.pending.has(key))
-      return;
-    const controller = new AbortController();
-    state.coverage.pending.set(key, controller);
-    notify();
-    try {
-      // Fetch and the one-time terrain-height table load run side by side,
-      // both handled from the start so an early tile failure is not unhandled.
-      const [bytes] = await Promise.all([
-        source.getTile('coverage', tile.z, tile.x, tile.y, {
-          signal: controller.signal,
-        }),
-        kind === 'sequence' ? ensureTerrainReady() : null,
-      ]);
-      // Only an abort, a retire, a clear or a newer request for this tile
-      // discards the bytes; a refresh that still wants the tile keeps them.
-      const current = () =>
-        state.coverage.pending.get(key) === controller &&
-        !state.coverage.tiles.has(key);
-      if (
-        controller.signal.aborted ||
-        !current() ||
-        kind !== state.coverage.kind ||
-        tile.z !== state.coverage.zoom
-      )
-        return;
-      const decoded = decodeCoverageTile(bytes, tile);
-      const entry = { kind, primitive: null, primitives: [], count: 0 };
-      // Padded: vector tiles carry a small buffer past their edge.
-      const bounds = tileBounds(tile.x, tile.y, tile.z);
-      const pad = (bounds.east - bounds.west) * 0.05;
-      entry.bounds = {
-        west: bounds.west - pad,
-        east: bounds.east + pad,
-        south: bounds.south - pad,
-        north: bounds.north + pad,
-      };
-      if (kind === 'sequence') {
-        // Newest first; the per-tile cap applies to what passes the filter.
-        entry.sequenceList = decoded.sequences.sort(
-          (a, b) => (b.capturedAt || 0) - (a.capturedAt || 0),
-        );
-        entry.sequences = new Map();
-        entry.total = decoded.sequences.length;
-      } else {
-        entry.points = decoded.overview;
-        entry.sequences = new Map();
-        entry.total = decoded.overview.length;
-      }
-      attachPrimitive(entry);
-      state.coverage.tiles.set(key, entry);
-      state.coverage.lastError = null;
-      requestRender();
-    } catch (error) {
-      if (
-        controller.signal.aborted ||
-        state.coverage.pending.get(key) !== controller
-      )
-        return;
-      state.coverage.lastError = error?.message || 'Coverage tile failed';
-      if (error?.keyRequired) state.keyRequired = true;
-      if (error?.keyRejected) {
-        // Every other tile would be refused too: stop asking.
-        state.keyRejected = true;
-        state.coverage.lastError = KEY_REJECTED_MESSAGE;
-      }
-      if (error?.retryAfterSec) holdFor(error.retryAfterSec);
-    } finally {
-      // Only the request that still owns the key settles it: a superseded one
-      // must not drop a newer request's entry (which is what counts as loading).
-      if (state.coverage.pending.get(key) === controller) {
-        state.coverage.pending.delete(key);
-        if (!state.coverage.pending.size) purgeStale();
-      }
-      notify();
-    }
-  }
-
-  /**
-   * Mapillary is rate-limiting: keep what is drawn, request nothing until the
-   * wait is over, then refresh once.
-   */
-  function holdFor(seconds) {
-    clearTimeout(state.coverage.holdTimer);
-    state.coverage.holdUntil = Date.now() + seconds * 1000;
-    state.coverage.lastError = RATE_LIMITED_MESSAGE;
-    state.coverage.holdTimer = setTimeout(() => {
-      state.coverage.holdTimer = null;
-      state.coverage.holdUntil = 0;
-      if (state.coverage.lastError === RATE_LIMITED_MESSAGE)
-        state.coverage.lastError = null;
-      refresh();
-    }, seconds * 1000);
-  }
-
-  /** Forget refusals when the provider goes off, so the next run asks again. */
-  function resetErrors() {
-    clearTimeout(state.coverage.holdTimer);
-    state.coverage.holdTimer = null;
-    state.coverage.holdUntil = 0;
-    state.coverage.lastError = null;
-    state.keyRejected = false;
-  }
-
-  /** Drop the previous zoom's tiles once the new ones are on screen. */
-  function purgeStale() {
-    clearTimeout(state.coverage.staleTimer);
-    state.coverage.staleTimer = null;
-    if (!state.coverage.stale.size) return;
-    for (const entry of state.coverage.stale.values()) detachPrimitive(entry);
-    state.coverage.stale.clear();
-    requestRender();
-  }
-
-  /** Move tiles to the stale set: the old zoom shows until the new one loads. */
-  function retire() {
-    for (const controller of state.coverage.pending.values())
-      controller.abort();
-    state.coverage.pending.clear();
-    for (const [key, entry] of state.coverage.tiles) {
-      cancelCast(entry);
-      const previous = state.coverage.stale.get(key);
-      if (previous) detachPrimitive(previous);
-      state.coverage.stale.set(key, entry);
-    }
-    state.coverage.tiles.clear();
-    clearTimeout(state.coverage.staleTimer);
-    state.coverage.staleTimer = setTimeout(purgeStale, STALE_TILE_MAX_MS);
-  }
-
-  function notify() {
-    state.context.notify();
-  }
-
-  /**
-   * Whether the screen centre meets the ground further ahead than the camera
-   * is high (a view tilted above 45°), or misses it.
-   */
-  function isTilted({ nadir, ahead }, height) {
-    if (!ahead) return true;
-    return metresBetween(nadir, ahead) > Math.max(1, height);
-  }
-
-  /** Recompute the tile set for the current camera and reconcile primitives. */
-  function refresh() {
-    const viewer = state.viewer;
-    if (!viewer || !state.context.isActive() || state.keyRequired) return;
-    if (state.statusKnown === false) return;
-    if (state.keyRejected || state.coverage.holdUntil > Date.now()) return;
-    const ground = groundUnderCamera(viewer, {
-      groundAt: state.context.groundCaster?.groundAt,
-    });
-    const cameraHeight = viewer.camera?.positionCartographic?.height;
-    const height = Number.isFinite(cameraHeight)
-      ? cameraHeight - (ground ?? 0)
-      : null;
-    const sequenceZoom = coverageZoomForHeight(height);
-    const overviewZoom = sequenceZoom ? null : overviewZoomForHeight(height);
-    const zoom = sequenceZoom ?? overviewZoom;
-    const kind = sequenceZoom ? 'sequence' : 'overview';
-    // At street zooms the rays meet the ground where it really is (1,600 m up
-    // in Denver; Google 3D hides the globe) and stop short of the horizon.
-    const ranged =
-      kind === 'sequence'
-        ? {
-            groundHeight: ground,
-            maxRange: Math.max(
-              SEQUENCE_VIEW_RANGE_MIN_M,
-              height * SEQUENCE_VIEW_RANGE_PER_HEIGHT,
-            ),
-          }
-        : {};
-    // Tilted street views rank tiles along the line of sight, from the ground
-    // under the camera to the ground at the centre of the screen.
-    const focus = kind === 'sequence' ? viewFocus(viewer, ranged) : null;
-    let bbox = visibleBbox(viewer, {
-      ...ranged,
-      // A tilted view's screen rows jump from the first metres to the horizon:
-      // keep the ground around the camera too. Looking down needs no help.
-      nearRange: focus && isTilted(focus, height) ? SEQUENCE_VIEW_NEAR_M : null,
-    });
-    if (kind === 'overview' && (!bbox || zoom <= 1))
-      bbox = [-180, -85, 180, 85];
-    if (zoom == null || !bbox) {
-      state.coverage.hint =
-        'Point the camera at the globe for street-level coverage';
-      clear();
-      notify();
-      return;
-    }
-    state.coverage.hint = '';
-    if (zoom !== state.coverage.zoom || kind !== state.coverage.kind) {
-      retire();
-      state.coverage.zoom = zoom;
-      state.coverage.kind = kind;
-    }
-    const { tiles } = tilesForBbox(bbox, zoom, {
-      limit:
-        kind === 'sequence' ? COVERAGE_MAX_TILES : COVERAGE_OVERVIEW_MAX_TILES,
-      focus: focus && { from: focus.nadir, to: focus.ahead },
-    });
-    const wanted = new Set(tiles.map(tileKey));
-    for (const key of [...state.coverage.tiles.keys()])
-      if (!wanted.has(key)) removeTile(key);
-    for (const [key, controller] of [...state.coverage.pending])
-      if (!wanted.has(key)) {
-        // The aborted request no longer owns its key, so its `finally` will
-        // not settle it: settle it here.
-        controller.abort();
-        state.coverage.pending.delete(key);
-      }
-    for (const tile of tiles) loadTile(tile, kind);
-    if (!state.coverage.pending.size) purgeStale();
-    // The camera moved: cells that were out of the sampler's range may not be,
-    // and lines left draped by a failed, partial or dropped cast get another try.
-    if (terrainMode())
-      for (const entry of state.coverage.tiles.values()) {
-        if (entry.castRequested) requestMesh(entry);
-        if (entry.drapedLines) castTile(entry, { retry: true });
-      }
-    notify();
-  }
-
-  function scheduleRefresh() {
-    clearTimeout(state.coverage.debounceTimer);
-    state.coverage.debounceTimer = setTimeout(
-      refresh,
-      COVERAGE_MOVE_DEBOUNCE_MS,
-    );
-  }
-
-  function attach(viewer) {
-    detach();
-    const remove = viewer.camera.changed.addEventListener(scheduleRefresh);
-    const removeEnd = viewer.camera.moveEnd.addEventListener(scheduleRefresh);
-    state.coverage.removeCameraListener = () => {
-      remove();
-      removeEnd();
-    };
-    refresh();
-  }
-
-  function detach() {
-    clearTimeout(state.coverage.debounceTimer);
-    state.coverage.debounceTimer = null;
-    state.coverage.removeCameraListener?.();
-    state.coverage.removeCameraListener = null;
-  }
-
-  function clear() {
-    for (const controller of state.coverage.pending.values())
-      controller.abort();
-    state.coverage.pending.clear();
-    for (const key of [...state.coverage.tiles.keys()]) removeTile(key);
-    purgeStale();
-    state.coverage.zoom = null;
-    state.coverage.kind = null;
-    clearTimeout(state.coverage.remeshTimer);
-    state.coverage.remeshTimer = null;
-    state.coverage.remeshDirty.clear();
-    stopSelectionWatch();
-    horizon.stop();
-    requestRender();
-  }
-
-  /** Rebuild every loaded tile from its decoded cache (after a filter change). */
-  function rebuild() {
-    purgeStale();
-    for (const entry of state.coverage.tiles.values()) {
-      cancelCast(entry);
-      entry.castRequested = false;
-      entry.meshParts = null;
-      detachPrimitive(entry);
-      attachPrimitive(entry);
-    }
-    requestRender();
-    notify();
-  }
-
-  /**
-   * Redraw tiles draped or cast for the new surface mode, then re-pick the
-   * zoom, since the ground height under the camera may have changed.
-   */
-  function setSurface() {
-    if (!state.context.isActive()) return;
-    rebuild();
-    refresh();
-  }
-
-  /** Recolour every part of a sequence in one ready primitive. */
-  function recolorInstances(primitive, sequence, selected) {
-    const value = sequenceColor({ selected });
-    for (const instanceId of partIds(sequence)) {
-      try {
-        const attributes = primitive.getGeometryInstanceAttributes(instanceId);
-        if (attributes)
-          attributes.color = Cesium.ColorGeometryInstanceAttribute.toValue(
-            value,
-            attributes.color,
-          );
-      } catch {
-        /* instance not in this primitive */
-      }
-    }
-  }
-
-  /** Every tile on the globe: the current zoom's and the stale zoom's. */
-  function drawnEntries() {
-    return [...state.coverage.tiles.values(), ...state.coverage.stale.values()];
-  }
-
-  /** A tile's primitives on the globe: its own, and the ones a swap still shows. */
-  function drawnRecords(entry) {
-    const records = entry.primitives || [];
-    return entry.swap ? [...records, ...entry.swap.old] : records;
-  }
-
-  /** Recolour one sequence, every part of it, in place (selection highlight). */
-  function recolorSequence(id, selected) {
-    for (const entry of drawnEntries()) {
-      const sequence = entry.sequences.get(id);
-      if (!sequence) continue;
-      for (const record of drawnRecords(entry)) {
-        // Still building: `syncSelection` catches it up once it is ready.
-        if (!record.primitive.ready) continue;
-        recolorInstances(record.primitive, sequence, selected);
-        if (selected) record.selectedId = id;
-        else if (record.selectedId === id) record.selectedId = null;
-      }
-    }
-    requestRender();
-  }
-
-  /**
-   * Bring a ready primitive's highlight up to the current selection, when
-   * it was built with another one (or none). True when it changed.
-   */
-  function syncSelection(entry, record) {
-    const current = state.sequence.selectedId ?? null;
-    if (record.selectedId === current || !record.primitive.ready) return false;
-    const previous =
-      record.selectedId && entry.sequences.get(record.selectedId);
-    if (previous) recolorInstances(record.primitive, previous, false);
-    const next = current && entry.sequences.get(current);
-    if (next) recolorInstances(record.primitive, next, true);
-    record.selectedId = current;
-    return true;
-  }
-
-  /**
-   * A primitive cannot be recoloured until it is ready, so while any is
-   * building, catch each one up with the selection as it becomes ready.
-   */
-  function watchSelection() {
-    const scene = state.viewer?.scene;
-    if (state.coverage.stopSelectionWatch || !scene?.postRender) return;
-    const stop = scene.postRender.addEventListener(() => {
-      let building = false;
-      let changed = false;
-      for (const entry of drawnEntries()) {
-        for (const record of entry.primitives || []) {
-          if (!record.primitive.ready) building = true;
-          else if (syncSelection(entry, record)) changed = true;
-        }
-        // Lines a swap still shows were ready (or never show): catch up only.
-        for (const record of entry.swap?.old || [])
-          if (syncSelection(entry, record)) changed = true;
-      }
-      if (changed) requestRender();
-      if (!building) stopSelectionWatch();
-    });
-    state.coverage.stopSelectionWatch = stop;
-  }
-
-  function stopSelectionWatch() {
-    state.coverage.stopSelectionWatch?.();
-    state.coverage.stopSelectionWatch = null;
-  }
-
-  /**
-   * Sequences (or overview points) drawn. A sequence that crosses a tile
-   * edge is in both tiles' lists, so sequences count once by id.
-   */
-  function sequenceCount() {
-    const ids = new Set();
-    let points = 0;
-    for (const entry of state.coverage.tiles.values())
-      if (entry.kind === 'sequence')
-        for (const id of entry.sequences.keys()) ids.add(id);
-      else points += entry.count;
-    return ids.size + points;
-  }
-
-  return {
-    attach,
-    detach,
-    refresh,
-    clear,
-    resetErrors,
-    rebuild,
-    setSurface,
-    recolorSequence,
-    sequenceCount,
-  };
 }

src/layers/streetLevel/providers/mapillary/policy.js

@@ -55,8 +55,6 @@ export const COVERAGE_LINE_WIDTH_PX = 2.5;
 
 /** Per-sequence image cones after a sequence is selected. */
 export const SEQUENCE_IMAGES_LIMIT = 2000;
-export const IMAGE_CONE_SIZE_PX = 26;
-export const IMAGE_CONE_MIN_SPACING_M = 3;
 
 /** Images asked for in a nearest-image search (radius: NEAREST_RADIUS_M). */
 export const NEAREST_LIMIT = 8;

src/layers/streetLevel/providers/mapillary/sequences.js

@@ -1,20 +1,7 @@
-import * as Cesium from 'cesium';
-import { imageConeGlyph } from '../../glyphs.js';
-import { passesImageryFilter } from '../../filter.js';
-import { refineHeights } from '../../groundCast.js';
-import { createHorizonCull, metresBetween } from '../../view.js';
-import { meshCellKey } from '../../meshSampler.js';
-import {
-  COLORS,
-  IMAGE_CONE_MIN_SPACING_M,
-  IMAGE_CONE_SIZE_PX,
-  PICK_PREFIX,
-} from './policy.js';
+import { createSequenceCones, thinImages } from '../../sequenceCones.js';
+import { COLORS, PICK_PREFIX } from './policy.js';
 
-const SPRITE_ID = 'street-level:mapillary-cones';
-
-/** How many recently viewed sequences keep their image list in memory. */
-const SEQUENCE_CACHE_SIZE = 40;
+export { thinImages } from '../../sequenceCones.js';
 
 /** Normalize a graph image record into the shape the cones use. */
 export function normalizeSequenceImage(record) {
@@ -33,290 +20,24 @@ export function normalizeSequenceImage(record) {
   };
 }
 
-/** Drop images closer than the spacing to the previous kept one. */
-export function thinImages(images, spacingM = IMAGE_CONE_MIN_SPACING_M) {
-  const kept = [];
-  let last = null;
-  for (const image of images) {
-    if (!last || metresBetween(last, image) >= spacingM) {
-      kept.push(image);
-      last = image;
-    }
-  }
-  return kept;
-}
-
-/** Image cones for one selected sequence. */
+/** Image cones for the selected Mapillary sequence, its line highlighted. */
 export function createSequences({ state, source, parts }) {
-  const { render, sprites } = state.services;
-
-  function requestRender() {
-    render?.governorRequestRender?.('mapillary-sequence');
-  }
-
-  function notify() {
-    state.context.notify();
-  }
-
-  const nothingDrawn = () => ({ images: [], cones: [], cells: new Set() });
-  /** Drawn cones, plus the mesh cells under them, so a sample moves only those. */
-  let drawn = nothingDrawn();
-
-  // The cones skip the depth test: hide the ones behind the globe.
-  const horizon = createHorizonCull({
-    getViewer: () => state.viewer,
-    items: () => drawn.cones.map((cone) => cone.billboard),
-    onChange: requestRender,
-  });
-
-  function ensureCollections(viewer) {
-    if (state.sequence.collection) return;
-    state.sequence.collection = new Cesium.BillboardCollection({
-      scene: viewer.scene,
-    });
-    viewer.scene.primitives.add(state.sequence.collection);
-    sprites?.registerSpriteCollection?.(SPRITE_ID, state.sequence.collection);
-  }
-
-  function clearCones() {
-    state.sequence.collection?.removeAll();
-    state.sequence.images = [];
-    drawn = nothingDrawn();
-    horizon.stop();
-  }
-
-  /** Where a cone stands: at `height`, or clamped to the ground when null. */
-  function placement(image, height) {
-    return {
-      position: Cesium.Cartesian3.fromDegrees(
-        image.lon,
-        image.lat,
-        height ?? 0,
-      ),
-      heightReference:
-        height === null
-          ? Cesium.HeightReference.CLAMP_TO_GROUND
-          : Cesium.HeightReference.NONE,
-    };
-  }
-
-  /**
-   * Terrain-mode cone heights on the street, not on roofs: bare earth refined
-   * by mesh samples. Null when draped or while terrain heights are fetched.
-   */
-  function coneHeights(images, { request = true } = {}) {
-    const ground = state.context.groundCaster;
-    if (state.context.getSurface?.() !== 'terrain' || !ground) return null;
-    const dems = images.map((image) => ground.groundAt(image.lon, image.lat));
-    if (dems.includes(null)) {
-      ground
-        .prepare(images.map((image) => [image.lon, image.lat]))
-        .then((ready) => {
-          if (ready && state.sequence.images === images) renderCones(images);
-        });
-      return null;
-    }
-    const sampler = state.context.meshSampler;
-    if (request)
-      sampler?.request(images.map((image) => [image.lon, image.lat]));
-    return refineHeights(
-      images.map((image, i) => ({
-        dem: dems[i],
-        mesh: sampler?.meshAt(image.lon, image.lat),
-      })),
-    );
-  }
-
-  function renderCones(images) {
-    const collection = state.sequence.collection;
-    if (!collection) return;
-    collection.removeAll();
-    drawn = { ...nothingDrawn(), images };
-    const heights = coneHeights(images);
-    // One colour per source; 360° images keep the ring shape.
-    const cone = imageConeGlyph({ size: 32, color: COLORS.coverage });
-    const ring = imageConeGlyph({
-      size: 32,
-      color: COLORS.coverage,
-      pano: true,
-    });
-    // Resolved now, so a "since N days" window keeps up with the clock.
-    const filter = state.context.getFilter();
-    images.forEach((image, index) => {
-      if (!passesImageryFilter(image, filter)) return;
-      const height = heights?.[index] ?? null;
-      const billboard = collection.add({
-        id: `${PICK_PREFIX.image}${image.id}`,
-        ...placement(image, height),
-        image: image.isPano ? ring : cone,
-        imageId: image.isPano ? 'mly-cone-pano' : 'mly-cone',
-        width: IMAGE_CONE_SIZE_PX,
-        height: IMAGE_CONE_SIZE_PX,
-        rotation: -Cesium.Math.toRadians(image.compassAngle),
-        alignedAxis: Cesium.Cartesian3.UNIT_Z,
-        disableDepthTestDistance: Number.POSITIVE_INFINITY,
-        verticalOrigin: Cesium.VerticalOrigin.CENTER,
-        scaleByDistance: new Cesium.NearFarScalar(200, 1.1, 6000, 0.35),
-      });
-      drawn.cones.push({ index, billboard, height });
-      drawn.cells.add(meshCellKey(image.lon, image.lat));
-    });
-    horizon.update();
-    requestRender();
-  }
-
-  /**
-   * Re-place cones whose height new mesh samples changed. A sample can move
-   * a neighbour too, so every height is recomputed but only moved cones touched.
-   */
-  function onMeshSampled(batch) {
-    if (state.context.getSurface?.() !== 'terrain' || !drawn.cones.length)
-      return;
-    if (!batch.some(([lon, lat]) => drawn.cells.has(meshCellKey(lon, lat))))
-      return;
-    const { images, cones } = drawn;
-    // Already asked for when drawn; a missing terrain cell redraws them all.
-    const heights = coneHeights(images, { request: false });
-    if (!heights) return;
-    const moved = [];
-    for (const cone of cones) {
-      const height = heights[cone.index] ?? null;
-      if (height === cone.height) continue;
-      cone.height = height;
-      const { position, heightReference } = placement(
-        images[cone.index],
-        height,
-      );
-      cone.billboard.heightReference = heightReference;
-      cone.billboard.position = position;
-      moved.push(cone.billboard);
-    }
-    if (!moved.length) return;
-    horizon.update(moved);
-    requestRender();
-  }
-
-  function remember(sequenceId, images) {
-    const { cache } = state.sequence;
-    cache.delete(sequenceId);
-    cache.set(sequenceId, images);
-    while (cache.size > SEQUENCE_CACHE_SIZE)
-      cache.delete(cache.keys().next().value);
-  }
-
-  /** Select a sequence: highlight its line and load its image cones. */
-  async function select(sequenceId) {
-    if (!sequenceId || !state.viewer) return;
-    // Already on screen, or already on its way.
-    if (
-      state.sequence.selectedId === sequenceId &&
-      (state.sequence.images.length || state.sequence.abort)
-    )
-      return;
-    if (state.sequence.selectedId && state.sequence.selectedId !== sequenceId)
-      parts.coverage.recolorSequence(state.sequence.selectedId, false);
-    state.sequence.abort?.abort();
-    state.sequence.selectedId = sequenceId;
-    parts.coverage.recolorSequence(sequenceId, true);
-    const cached = state.sequence.cache.get(sequenceId);
-    if (cached) {
-      state.sequence.abort = null;
-      state.sequence.loading = false;
-      state.sequence.images = cached;
-      renderCones(cached);
-      state.context.actions.reportError(null);
-      notify();
-      return;
-    }
-    // The previous sequence's cones must not stay clickable under the new
-    // highlight while this one loads, nor after its load fails.
-    clearCones();
-    requestRender();
-    const controller = new AbortController();
-    state.sequence.abort = controller;
-    state.sequence.loading = true;
-    notify();
-    try {
-      const records = await source.getSequenceImages(sequenceId, {
-        signal: controller.signal,
-      });
-      if (controller.signal.aborted) return;
-      const images = thinImages(
+  return createSequenceCones({
+    state,
+    async loadImages(sequenceId, { signal }) {
+      const records = await source.getSequenceImages(sequenceId, { signal });
+      return thinImages(
         records
           .map(normalizeSequenceImage)
           .filter(Boolean)
           .sort((a, b) => a.capturedAt - b.capturedAt),
       );
-      remember(sequenceId, images);
-      state.sequence.images = images;
-      renderCones(images);
-      state.context.actions.reportError(null);
-    } catch (error) {
-      if (!controller.signal.aborted) {
-        // Nothing to show: drop the highlight, so a click asks again.
-        parts.coverage.recolorSequence(sequenceId, false);
-        state.sequence.selectedId = null;
-        state.context.actions.reportError(
-          error?.message || 'Sequence images unavailable',
-        );
-      }
-    } finally {
-      if (state.sequence.abort === controller) {
-        state.sequence.loading = false;
-        state.sequence.abort = null;
-      }
-      notify();
-    }
-  }
-
-  function clearSelection() {
-    state.sequence.abort?.abort();
-    state.sequence.abort = null;
-    if (state.sequence.selectedId)
-      parts.coverage.recolorSequence(state.sequence.selectedId, false);
-    state.sequence.selectedId = null;
-    state.sequence.loading = false;
-    clearCones();
-    // An error about the sequence goes with it.
-    state.context.actions.reportError(null);
-    requestRender();
-    notify();
-  }
-
-  /** Re-draw the current sequence's cones (after an imagery filter change). */
-  function rerender() {
-    if (state.sequence.images.length) renderCones(state.sequence.images);
-  }
-
-  // New mesh samples may move the cones onto (or off) the road surface.
-  const stopMeshListener = state.context.meshSampler?.onSampled(onMeshSampled);
-
-  function setVisible(visible) {
-    if (state.sequence.collection) state.sequence.collection.show = visible;
-    requestRender();
-  }
-
-  function destroy(viewer) {
-    state.sequence.abort?.abort();
-    horizon.stop();
-    drawn = nothingDrawn();
-    stopMeshListener?.();
-    const collection = state.sequence.collection;
-    if (collection) {
-      sprites?.unregisterSpriteCollection?.(SPRITE_ID, collection);
-      viewer?.scene?.primitives?.remove(collection);
-      state.sequence.collection = null;
-    }
-    state.sequence.images = [];
-    state.sequence.selectedId = null;
-  }
-
-  return {
-    ensureCollections,
-    select,
-    clearSelection,
-    rerender,
-    setVisible,
-    destroy,
-  };
+    },
+    colors: COLORS,
+    pickPrefix: PICK_PREFIX.image,
+    spriteId: 'street-level:mapillary-cones',
+    renderKey: 'mapillary-sequence',
+    onHighlight: (sequenceId, selected) =>
+      parts.coverage.recolorSequence(sequenceId, selected),
+  });
 }

src/layers/streetLevel/registry.js

@@ -22,6 +22,9 @@ export function filtersOf(provider) {
  * @property {boolean} [defaultOn]     Default true.
  * @property {{kind: 'view-cone', color: string}} [marker]   Default: GEV's pin.
  * @property {Array<'pano'|'since'>} [filters]   Filters it honours (default both).
+ * @property {{noun: string, action: string}} [coverageLabel]   How the panel counts its lines and says what a click does (default: sequences, "click a line for its photos").
+ * @property {boolean} [highlightsSequence]   Its lines show the selected sequence (default true; the legend's "Selected" needs one).
+ * @property {'capture'|'upload'} [sinceBasis]   What SINCE compares (default 'capture'); 'upload' puts a note under the slider while the provider is lit.
  * @property {(context: ProviderContext) => ProviderInstance} create
  *
  * @typedef {object} ProviderContext   Handed to `create()` once by the core.
@@ -32,7 +35,7 @@ export function filtersOf(provider) {
  * @property {GroundCaster|null} groundCaster   Bare-earth heights for terrain mode (groundCast.js); null without a terrain service.
  * @property {{meshAt: (lon: number, lat: number) => number|undefined, request: (points: Array<[number, number]>) => void, onSampled: (listener: (cells: Array<[number, number]>) => void) => () => void}|null} meshSampler   Sampled Google 3D surface heights (meshSampler.js); pass `meshAt` to `castLine`.
  * @property {() => void} notify       Ask the core to publish a new UI snapshot.
- * @property {{openImage: (imageId: string) => Promise<void>, reportError: (message: string|null) => void}} actions
+ * @property {{openImage: (imageId: string, options?: {frame?: boolean}) => Promise<boolean>, openNearest: (point: {lon: number, lat: number}) => Promise<boolean>, reportError: (message: string|null) => void}} actions
  *
  * @typedef {object} ProviderInstance
  * @property {() => Promise<{configured: boolean}>} status
@@ -44,7 +47,7 @@ export function filtersOf(provider) {
  * @property {(filter: {pano: string, sinceMs: number|null}) => void} setFilter   The filter changed: redraw (reading `getFilter()`).
  * @property {(mode: 'draped'|'terrain') => void} [setSurface]   Redraw coverage and cones for the new surface mode.
  * @property {() => {count: number, zoom: number|null, kind: string|null, loading: boolean, hint: string, error: string|null, keyRequired: boolean}} coverageStats
- * @property {(pickId: string) => boolean} handlePick   The id carries the provider's own prefix.
+ * @property {(pickId: string, click?: {groundPoint: () => {lon: number, lat: number}|null}) => boolean} handlePick   The id carries the provider's own prefix; `groundPoint` is where the click met the ground.
  * @property {(sequenceId: string) => Promise<void>} [selectSequence]
  * @property {() => void} [clearSequence]
  * @property {() => {selectedId: string|null, images: number, loading: boolean}} [sequenceStats]
@@ -65,6 +68,7 @@ export function filtersOf(provider) {
  * @property {() => void} resize
  * @property {(host: HTMLElement) => Promise<void>} [prewarm]
  * @property {(mode: 'letterbox'|'fill') => void} [setRenderMode]
+ * @property {() => boolean} [supportsRenderModes]   False while the image has no frame to fit (a panorama): FIT / FILL hide.
  * @property {(listener: (pose: StreetPose) => void) => () => void} onPose
  *
  * @typedef {object} StreetPose
@@ -157,6 +161,14 @@ export function validateProviders(providers) {
       throw new TypeError(
         `Street Level provider ${label}: filters must list ${IMAGERY_FILTERS.join(' or ')}`,
       );
+    if (
+      provider.sinceBasis !== undefined &&
+      provider.sinceBasis !== 'capture' &&
+      provider.sinceBasis !== 'upload'
+    )
+      throw new TypeError(
+        `Street Level provider ${label}: sinceBasis must be 'capture' or 'upload'`,
+      );
     ids.add(provider.id);
     prefixes.push(provider.pickPrefix);
   }

src/layers/streetLevel/registry.test.mjs

@@ -117,4 +117,9 @@ test('a provider may narrow the filters it honours and pick a view-cone marker',
     () => validateProviders([def({ marker: { kind: 'pegman' } })]),
     /marker must be/,
   );
+  validateProviders([def({ sinceBasis: 'upload' })]);
+  assert.throws(
+    () => validateProviders([def({ sinceBasis: 'shot' })]),
+    /sinceBasis must be 'capture' or 'upload'/,
+  );
 });

src/layers/streetLevel/selection.js

@@ -28,7 +28,24 @@ export function createSelection({ state, parts }) {
     }
     const entry = state.providers.get(route.providerId);
     if (!entry?.on) return;
-    route.instance.handlePick(route.id);
+    route.instance.handlePick(route.id, {
+      groundPoint: () => groundPointAt(viewer, click.position),
+    });
+  }
+
+  /** Lon/lat of the ground under a screen point, or null (sky, no picker). */
+  function groundPointAt(viewer, screenPosition) {
+    const position = state.services.scenePick?.pickGroundPosition?.(
+      viewer,
+      screenPosition,
+    );
+    const carto = position && Cesium.Cartographic.fromCartesian(position);
+    return carto
+      ? {
+          lon: Cesium.Math.toDegrees(carto.longitude),
+          lat: Cesium.Math.toDegrees(carto.latitude),
+        }
+      : null;
   }
 
   /**

src/layers/streetLevel/selection.test.mjs

@@ -8,7 +8,12 @@ import { createSelection } from './selection.js';
  * `frame()` runs them; timers and Date.now() are mocked so a burst of moves
  * has a known timeline.
  */
-function harness({ selected = false } = {}) {
+function harness({
+  selected = false,
+  router = null,
+  providers = new Map(),
+  services = {},
+} = {}) {
   const saved = {
     document: globalThis.document,
     requestAnimationFrame: globalThis.requestAnimationFrame,
@@ -60,12 +65,16 @@ function harness({ selected = false } = {}) {
     viewer,
     enabled: true,
     clickHandler: null,
-    services: { picking: null, input: null },
+    providers,
+    services: { picking: null, input: null, ...services },
   };
   const selection = createSelection({
     state,
     parts: {
-      router: { ownsPick: (id) => id === 'mly:seq:1', resolve: () => null },
+      router: router || {
+        ownsPick: (id) => id === 'mly:seq:1',
+        resolve: () => null,
+      },
       hasSelectedSequence: () => sequences.selected,
       openAtGround: (position, picked) =>
         groundClicks.push({ position, picked }),
@@ -282,3 +291,43 @@ test('a click on nothing of ours goes to the ground handler with the pick, which
     h.restore();
   }
 });
+
+test('a click on a provider line hands it the ground under the click, measured only if asked', () => {
+  const handled = [];
+  const instance = {
+    handlePick: (id, click) => handled.push({ id, click }),
+  };
+  const groundPicks = [];
+  const h = harness({
+    router: {
+      ownsPick: () => true,
+      resolve: (id) => ({ providerId: 'kartaview', instance, id }),
+    },
+    providers: new Map([['kartaview', { on: true }]]),
+    services: {
+      scenePick: {
+        pickGroundPosition: (viewer, position) => {
+          groundPicks.push(position);
+          return Cesium.Cartesian3.fromDegrees(-83.0458, 42.3314, 190);
+        },
+      },
+    },
+  });
+  try {
+    h.scene.under = 'kv:line:14/1/2/3';
+    h.click(40);
+    assert.equal(handled.length, 1);
+    assert.equal(handled[0].id, 'kv:line:14/1/2/3');
+    assert.equal(
+      groundPicks.length,
+      0,
+      'no depth read until the provider asks',
+    );
+    const point = handled[0].click.groundPoint();
+    assert.ok(Math.abs(point.lon + 83.0458) < 1e-9);
+    assert.ok(Math.abs(point.lat - 42.3314) < 1e-9);
+    assert.deepEqual(groundPicks, [{ x: 40, y: 10 }]);
+  } finally {
+    h.restore();
+  }
+});

src/layers/streetLevel/sequenceCones.js

@@ -0,0 +1,334 @@
+import * as Cesium from 'cesium';
+import { imageConeGlyph } from './glyphs.js';
+import { passesImageryFilter } from './filter.js';
+import { refineHeights } from './groundCast.js';
+import { createHorizonCull, metresBetween } from './view.js';
+import { meshCellKey } from './meshSampler.js';
+
+/** How many recently viewed sequences keep their image list in memory. */
+const SEQUENCE_CACHE_SIZE = 40;
+
+/** Cones closer than this to the previous kept one are dropped. */
+export const IMAGE_CONE_MIN_SPACING_M = 3;
+export const IMAGE_CONE_SIZE_PX = 26;
+
+/**
+ * @typedef {object} ConeImage   One image of a sequence, as the cones draw it.
+ * @property {string} id
+ * @property {number} lon
+ * @property {number} lat
+ * @property {number} compassAngle   Degrees clockwise from north.
+ * @property {number} capturedAt     Epoch ms (0 when unknown).
+ * @property {boolean} isPano
+ */
+
+/** Drop images closer than the spacing to the previous kept one. */
+export function thinImages(images, spacingM = IMAGE_CONE_MIN_SPACING_M) {
+  const kept = [];
+  let last = null;
+  for (const image of images) {
+    if (!last || metresBetween(last, image) >= spacingM) {
+      kept.push(image);
+      last = image;
+    }
+  }
+  return kept;
+}
+
+/**
+ * Image cones for one selected sequence, any provider's. A cone's pick id is
+ * `pickPrefix` + the image id; 360° images draw as rings.
+ *
+ * @param {object} options
+ * @param {object} options.state  Provider state: `context`, `services`, `viewer`, `sequence`.
+ * @param {(sequenceId: string, init: {signal: AbortSignal}) => Promise<Array<ConeImage>>} options.loadImages
+ *   The sequence's images in capture order, thinned (see `thinImages`).
+ * @param {{coverage: string}} options.colors
+ * @param {string} options.pickPrefix   Pick-id prefix of the cones.
+ * @param {string} options.spriteId     Sprite-order id of the cone collection.
+ * @param {string} options.renderKey    Render-governor reason.
+ * @param {(sequenceId: string, selected: boolean) => void} [options.onHighlight]
+ *   Highlight (or stop highlighting) the sequence's coverage line.
+ * @param {(image: ConeImage, filter: object) => boolean} [options.passes]
+ *   Whether the imagery filter keeps a cone.
+ */
+export function createSequenceCones({
+  state,
+  loadImages,
+  colors,
+  pickPrefix,
+  spriteId,
+  renderKey,
+  onHighlight = () => {},
+  passes = passesImageryFilter,
+}) {
+  const { render, sprites } = state.services;
+
+  function requestRender() {
+    render?.governorRequestRender?.(renderKey);
+  }
+
+  function notify() {
+    state.context.notify();
+  }
+
+  const nothingDrawn = () => ({ images: [], cones: [], cells: new Set() });
+  /** Drawn cones, plus the mesh cells under them, so a sample moves only those. */
+  let drawn = nothingDrawn();
+
+  // The cones skip the depth test: hide the ones behind the globe.
+  const horizon = createHorizonCull({
+    getViewer: () => state.viewer,
+    items: () => drawn.cones.map((cone) => cone.billboard),
+    onChange: requestRender,
+  });
+
+  function ensureCollections(viewer) {
+    if (state.sequence.collection) return;
+    state.sequence.collection = new Cesium.BillboardCollection({
+      scene: viewer.scene,
+    });
+    viewer.scene.primitives.add(state.sequence.collection);
+    sprites?.registerSpriteCollection?.(spriteId, state.sequence.collection);
+  }
+
+  function clearCones() {
+    state.sequence.collection?.removeAll();
+    state.sequence.images = [];
+    drawn = nothingDrawn();
+    horizon.stop();
+  }
+
+  /** Where a cone stands: at `height`, or clamped to the ground when null. */
+  function placement(image, height) {
+    return {
+      position: Cesium.Cartesian3.fromDegrees(
+        image.lon,
+        image.lat,
+        height ?? 0,
+      ),
+      heightReference:
+        height === null
+          ? Cesium.HeightReference.CLAMP_TO_GROUND
+          : Cesium.HeightReference.NONE,
+    };
+  }
+
+  /**
+   * Terrain-mode cone heights on the street, not on roofs: bare earth refined
+   * by mesh samples. Null when draped or while terrain heights are fetched.
+   */
+  function coneHeights(images, { request = true } = {}) {
+    const ground = state.context.groundCaster;
+    if (state.context.getSurface?.() !== 'terrain' || !ground) return null;
+    const dems = images.map((image) => ground.groundAt(image.lon, image.lat));
+    if (dems.includes(null)) {
+      ground
+        .prepare(images.map((image) => [image.lon, image.lat]))
+        .then((ready) => {
+          if (ready && state.sequence.images === images) renderCones(images);
+        });
+      return null;
+    }
+    const sampler = state.context.meshSampler;
+    if (request)
+      sampler?.request(images.map((image) => [image.lon, image.lat]));
+    return refineHeights(
+      images.map((image, i) => ({
+        dem: dems[i],
+        mesh: sampler?.meshAt(image.lon, image.lat),
+      })),
+    );
+  }
+
+  function renderCones(images) {
+    const collection = state.sequence.collection;
+    if (!collection) return;
+    collection.removeAll();
+    drawn = { ...nothingDrawn(), images };
+    const heights = coneHeights(images);
+    // One colour per source; 360° images keep the ring shape.
+    const cone = imageConeGlyph({ size: 32, color: colors.coverage });
+    const ring = imageConeGlyph({
+      size: 32,
+      color: colors.coverage,
+      pano: true,
+    });
+    // Resolved now, so a "since N days" window keeps up with the clock.
+    const filter = state.context.getFilter();
+    images.forEach((image, index) => {
+      if (!passes(image, filter)) return;
+      const height = heights?.[index] ?? null;
+      const billboard = collection.add({
+        id: `${pickPrefix}${image.id}`,
+        ...placement(image, height),
+        image: image.isPano ? ring : cone,
+        imageId: image.isPano ? `${spriteId}:pano` : `${spriteId}:flat`,
+        width: IMAGE_CONE_SIZE_PX,
+        height: IMAGE_CONE_SIZE_PX,
+        rotation: -Cesium.Math.toRadians(image.compassAngle),
+        alignedAxis: Cesium.Cartesian3.UNIT_Z,
+        disableDepthTestDistance: Number.POSITIVE_INFINITY,
+        verticalOrigin: Cesium.VerticalOrigin.CENTER,
+        scaleByDistance: new Cesium.NearFarScalar(200, 1.1, 6000, 0.35),
+      });
+      drawn.cones.push({ index, billboard, height });
+      drawn.cells.add(meshCellKey(image.lon, image.lat));
+    });
+    horizon.update();
+    requestRender();
+  }
+
+  /**
+   * Re-place cones whose height new mesh samples changed. A sample can move
+   * a neighbour too, so every height is recomputed but only moved cones touched.
+   */
+  function onMeshSampled(batch) {
+    if (state.context.getSurface?.() !== 'terrain' || !drawn.cones.length)
+      return;
+    if (!batch.some(([lon, lat]) => drawn.cells.has(meshCellKey(lon, lat))))
+      return;
+    const { images, cones } = drawn;
+    // Already asked for when drawn; a missing terrain cell redraws them all.
+    const heights = coneHeights(images, { request: false });
+    if (!heights) return;
+    const moved = [];
+    for (const cone of cones) {
+      const height = heights[cone.index] ?? null;
+      if (height === cone.height) continue;
+      cone.height = height;
+      const { position, heightReference } = placement(
+        images[cone.index],
+        height,
+      );
+      cone.billboard.heightReference = heightReference;
+      cone.billboard.position = position;
+      moved.push(cone.billboard);
+    }
+    if (!moved.length) return;
+    horizon.update(moved);
+    requestRender();
+  }
+
+  function remember(sequenceId, images) {
+    const { cache } = state.sequence;
+    cache.delete(sequenceId);
+    cache.set(sequenceId, images);
+    while (cache.size > SEQUENCE_CACHE_SIZE)
+      cache.delete(cache.keys().next().value);
+  }
+
+  /**
+   * Select a sequence: highlight its line and load its image cones. `force`
+   * reloads a selected one (a provider that loads part of a sequence moved on).
+   */
+  async function select(sequenceId, { force = false } = {}) {
+    if (!sequenceId || !state.viewer) return;
+    // Already on screen, or already on its way.
+    if (
+      !force &&
+      state.sequence.selectedId === sequenceId &&
+      (state.sequence.images.length || state.sequence.abort)
+    )
+      return;
+    if (state.sequence.selectedId && state.sequence.selectedId !== sequenceId)
+      onHighlight(state.sequence.selectedId, false);
+    state.sequence.abort?.abort();
+    state.sequence.selectedId = sequenceId;
+    onHighlight(sequenceId, true);
+    const cached = force ? null : state.sequence.cache.get(sequenceId);
+    if (cached) {
+      state.sequence.abort = null;
+      state.sequence.loading = false;
+      state.sequence.images = cached;
+      renderCones(cached);
+      state.context.actions.reportError(null);
+      notify();
+      return;
+    }
+    // The previous sequence's cones must not stay clickable under the new
+    // highlight while this one loads, nor after its load fails.
+    clearCones();
+    requestRender();
+    const controller = new AbortController();
+    state.sequence.abort = controller;
+    state.sequence.loading = true;
+    notify();
+    try {
+      const images = await loadImages(sequenceId, {
+        signal: controller.signal,
+      });
+      if (controller.signal.aborted) return;
+      remember(sequenceId, images);
+      state.sequence.images = images;
+      renderCones(images);
+      state.context.actions.reportError(null);
+    } catch (error) {
+      if (!controller.signal.aborted) {
+        // Nothing to show: drop the highlight, so a click asks again.
+        onHighlight(sequenceId, false);
+        state.sequence.selectedId = null;
+        state.context.actions.reportError(
+          error?.message || 'Sequence images unavailable',
+        );
+      }
+    } finally {
+      if (state.sequence.abort === controller) {
+        state.sequence.loading = false;
+        state.sequence.abort = null;
+      }
+      notify();
+    }
+  }
+
+  function clearSelection() {
+    state.sequence.abort?.abort();
+    state.sequence.abort = null;
+    if (state.sequence.selectedId)
+      onHighlight(state.sequence.selectedId, false);
+    state.sequence.selectedId = null;
+    state.sequence.loading = false;
+    clearCones();
+    // An error about the sequence goes with it.
+    state.context.actions.reportError(null);
+    requestRender();
+    notify();
+  }
+
+  /** Re-draw the current sequence's cones (after an imagery filter change). */
+  function rerender() {
+    if (state.sequence.images.length) renderCones(state.sequence.images);
+  }
+
+  // New mesh samples may move the cones onto (or off) the road surface.
+  const stopMeshListener = state.context.meshSampler?.onSampled(onMeshSampled);
+
+  function setVisible(visible) {
+    if (state.sequence.collection) state.sequence.collection.show = visible;
+    requestRender();
+  }
+
+  function destroy(viewer) {
+    state.sequence.abort?.abort();
+    horizon.stop();
+    drawn = nothingDrawn();
+    stopMeshListener?.();
+    const collection = state.sequence.collection;
+    if (collection) {
+      sprites?.unregisterSpriteCollection?.(spriteId, collection);
+      viewer?.scene?.primitives?.remove(collection);
+      state.sequence.collection = null;
+    }
+    state.sequence.images = [];
+    state.sequence.selectedId = null;
+  }
+
+  return {
+    ensureCollections,
+    select,
+    clearSelection,
+    rerender,
+    setVisible,
+    destroy,
+  };
+}

src/layers/streetLevel/uiState.js

@@ -17,6 +17,9 @@ import { COLORS } from './policy.js';
  * @property {string} color   The source's one colour.
  * @property {boolean} [groundClick]
  * @property {Array<'pano'|'since'>} [filters]
+ * @property {{noun: string, action: string}|null} [coverageLabel]
+ * @property {boolean} [highlightsSequence]   Its lines turn cyan when their sequence is selected.
+ * @property {'capture'|'upload'} [sinceBasis]   What its SINCE compares.
  */
 
 /**
@@ -34,6 +37,8 @@ export function summarizeCoverage(providers) {
         ? 'No street-level imagery providers configured'
         : [...new Set(active.map((p) => p.hint).filter(Boolean))].join(' · '),
     error: active.find((p) => p.error)?.error || null,
+    // One source is lit at a time; its wording counts the lines.
+    label: active.find((p) => p.coverageLabel)?.coverageLabel || null,
     keyRequired:
       active.length > 0 && active.every((p) => p.keyRequired === true),
     keyRejected:
@@ -68,6 +73,18 @@ export function filterControls(providers) {
   return { pano: honoured('pano'), since: honoured('since') };
 }
 
+/**
+ * The note under SINCE when a lit provider dates its imagery by upload,
+ * e.g. "KartaView: by upload date", or null.
+ * @param {Array<ProviderSnapshot>} providers
+ */
+export function sinceNote(providers) {
+  const names = providers
+    .filter((p) => p.on && p.sinceBasis === 'upload')
+    .map((p) => p.name);
+  return names.length ? `${names.join(', ')}: by upload date` : null;
+}
+
 /**
  * The panel snapshot from core state and provider snapshots. The legend has
  * one swatch per active source that draws coverage lines, then Selected.
@@ -92,7 +109,13 @@ export function composeUIState({
       label: provider.name,
       color: provider.color,
     }));
-  if (legend.length)
+  // "Selected" only beside a source whose lines turn cyan when selected.
+  if (
+    active.some(
+      (provider) =>
+        provider.groundClick !== true && provider.highlightsSequence !== false,
+    )
+  )
     legend.push({ key: 'selected', label: 'Selected', color: COLORS.selected });
   return {
     enabled,
@@ -102,6 +125,7 @@ export function composeUIState({
     keyRejected,
     filter: { ...filter },
     filterControls: filterControls(providers),
+    sinceNote: sinceNote(providers),
     providers: providers.map((p) => ({ ...p })),
     coverage,
     legend,

src/layers/streetLevel/uiState.test.mjs

@@ -128,6 +128,18 @@ test('the filter controls show only for a lit provider that honours them', () =>
   );
 });
 
+test('a lit provider that dates by upload puts a note under SINCE', () => {
+  const kartaView = provider({
+    id: 'kartaview',
+    name: 'KartaView',
+    sinceBasis: 'upload',
+  });
+  const note = (providers) => composeUIState({ ...base, providers }).sinceNote;
+  assert.equal(note([provider()]), null, 'Mapillary: capture date');
+  assert.equal(note([kartaView]), 'KartaView: by upload date');
+  assert.equal(note([{ ...kartaView, on: false }]), null, 'only while lit');
+});
+
 test('hint and error come from the first active provider that has one', () => {
   const ui = composeUIState({
     ...base,
@@ -154,6 +166,7 @@ test('summarizeCoverage is what getStats reports, without building a snapshot',
       loading: true,
       hint: 'Look down',
       error: 'boom',
+      label: null,
       keyRequired: false,
       keyRejected: false,
     },
@@ -235,3 +248,25 @@ test('a key-gated layer offers the switched-off sources that would draw with a k
     [],
   );
 });
+
+test('a source whose lines never show a selection lists no Selected swatch, and names its own lines', () => {
+  const kartaView = provider({
+    id: 'kartaview',
+    name: 'KartaView',
+    color: '#635bff',
+    highlightsSequence: false,
+    coverageLabel: {
+      noun: 'streets',
+      action: 'click a line for its nearest photo',
+    },
+  });
+  const ui = composeUIState({ ...base, providers: [kartaView] });
+  assert.deepEqual(
+    ui.legend.map((entry) => entry.key),
+    ['kartaview'],
+  );
+  assert.deepEqual(ui.coverage.label, {
+    noun: 'streets',
+    action: 'click a line for its nearest photo',
+  });
+});

src/layers/streetLevel/viewerHost.js

@@ -39,6 +39,10 @@ export function createViewerHost({ state, parts }) {
       sequenceId: pose.sequenceId ?? null,
       creator: pose.creator || null,
       externalUrl: pose.externalUrl || null,
+      // FIT / FILL, unless this image has no frame to fit (a panorama).
+      renderModes:
+        typeof active.adapter.setRenderMode === 'function' &&
+        active.adapter.supportsRenderModes?.() !== false,
     });
     parts.marker.set(
       state.street.position,

src/layers/streetLevel/viewerHost.test.mjs

@@ -659,3 +659,17 @@ test('FIT/FILL stays hidden for a second Street View panorama after a close', as
   await host.open('google', 'g-2');
   assert.equal(state.street.renderModes, false);
 });
+
+test('an adapter that can frame but says this image has no frame offers no FIT / FILL', async () => {
+  const adapter = fakeAdapter();
+  let frameable = false;
+  adapter.setRenderMode = () => {};
+  adapter.supportsRenderModes = () => frameable;
+  const { state, host } = harness(adapter);
+  await host.open('mapillary', 'pano-1');
+  assert.equal(state.street.imageId, 'pano-1', 'the pose arrived');
+  assert.equal(state.street.renderModes, false);
+  frameable = true;
+  await host.open('mapillary', 'flat-1');
+  assert.equal(state.street.renderModes, true, 'a flat image can be framed');
+});

src/sources/gbfsStations.js

@@ -50,6 +50,26 @@ export function extractStationsArray(payload) {
   return [];
 }
 
+/** Read legacy text or a GBFS v3 Localized String, preferring usable English text. */
+function stationName(value) {
+  if (typeof value === 'string') return value.trim();
+  if (!Array.isArray(value)) return '';
+
+  let fallback = '';
+  for (const translation of value) {
+    if (typeof translation?.text !== 'string') continue;
+    const text = translation.text.trim();
+    if (!text) continue;
+    if (!fallback) fallback = text;
+    if (
+      typeof translation.language === 'string' &&
+      /^en(?:-|$)/i.test(translation.language.trim())
+    )
+      return text;
+  }
+  return fallback;
+}
+
 /**
  * Parse a GBFS station_information payload into a Map of station metadata.
  * Handles field-name variations across different GBFS providers
@@ -63,7 +83,7 @@ export function parseStationInformation(payload) {
   const stationMap = new Map();
 
   for (const raw of stations) {
-    // Accept both GBFS 2.x (station_id) and alternate (id) field names
+    // Accept both GBFS (station_id) and alternate (id) field names
     const stationId = String(raw?.station_id ?? raw?.id ?? '').trim();
     const lat = Number(raw?.lat ?? raw?.latitude);
     const lon = Number(raw?.lon ?? raw?.longitude);
@@ -71,7 +91,7 @@ export function parseStationInformation(payload) {
 
     stationMap.set(stationId, {
       stationId,
-      name: String(raw?.name || raw?.short_name || '').trim(),
+      name: stationName(raw?.name) || stationName(raw?.short_name),
       lat,
       lon,
       capacity: toNonNegativeInteger(raw?.capacity),

src/sources/gbfsStations.test.mjs

@@ -0,0 +1,199 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { parseStationInformation } from './gbfsStations.js';
+
+const station = (fields = {}) => ({
+  station_id: 's1',
+  lat: 30.2681,
+  lon: -97.7469,
+  capacity: 13,
+  ...fields,
+});
+const parseName = (fields, version) =>
+  parseStationInformation({
+    version,
+    data: { stations: [station(fields)] },
+  }).get('s1').name;
+
+test('GBFS v2 station names remain trimmed strings', () => {
+  assert.equal(
+    parseName({ name: ' Republic Square ', short_name: 'Short' }, '2.3'),
+    'Republic Square',
+  );
+});
+
+test('GBFS v3 station names prefer English over the first translation', () => {
+  assert.equal(
+    parseName(
+      {
+        name: [
+          { language: 'hu', text: 'Köztársaság tér' },
+          { language: 'en', text: ' Republic Square ' },
+        ],
+      },
+      '3.0',
+    ),
+    'Republic Square',
+  );
+});
+
+test('English preference accepts case differences and regional language tags', () => {
+  for (const language of ['EN', 'en-GB', 'En-US']) {
+    assert.equal(
+      parseName({
+        name: [
+          { language: 'hu', text: 'Hungarian' },
+          { language, text: 'English' },
+        ],
+      }),
+      'English',
+    );
+  }
+});
+
+test('without usable English text the first usable translation wins', () => {
+  assert.equal(
+    parseName({
+      name: [
+        null,
+        { language: 'en', text: '  ' },
+        { language: 'en', text: 42 },
+        { language: 'hu', text: ' Első ' },
+        { language: 'fr', text: 'Deuxième' },
+      ],
+    }),
+    'Első',
+  );
+});
+
+test('malformed language fields cannot abort translation selection', () => {
+  const name = [
+    null,
+    false,
+    'bad',
+    {},
+    { language: 42, text: 'Fallback' },
+    { language: { unexpected: true }, text: 'Other' },
+    { language: 'en', text: 'English' },
+  ];
+  assert.equal(parseName({ name }), 'English');
+  assert.equal(
+    parseName({ name: [{ text: ' Usable text without a locale ' }] }),
+    'Usable text without a locale',
+  );
+});
+
+test('a usable name takes precedence over an English short name', () => {
+  assert.equal(
+    parseName({
+      name: [{ language: 'hu', text: 'Full name' }],
+      short_name: [{ language: 'en', text: 'Short name' }],
+    }),
+    'Full name',
+  );
+});
+
+test('missing, empty and malformed names fall back to localized short_name', () => {
+  for (const name of [
+    undefined,
+    null,
+    '',
+    '  ',
+    [],
+    {},
+    0,
+    42,
+    false,
+    [null, {}, { language: 'en', text: [] }, { language: 'hu', text: ' ' }],
+  ]) {
+    assert.equal(
+      parseName({
+        name,
+        short_name: [
+          { language: 'hu', text: 'Rövid' },
+          { language: 'en', text: ' Short ' },
+        ],
+      }),
+      'Short',
+    );
+  }
+});
+
+test('localized names can fall back to legacy short_name strings', () => {
+  assert.equal(parseName({ name: [], short_name: ' Short ' }), 'Short');
+});
+
+test('no usable name leaves the station available with an empty name', () => {
+  for (const value of [
+    undefined,
+    null,
+    '',
+    [],
+    {},
+    42,
+    true,
+    [null, { text: false }, { language: 'en', text: ' ' }],
+  ]) {
+    assert.equal(parseName({ name: value, short_name: value }), '');
+  }
+});
+
+test('name shape is normalized even when a feed omits or misstates its version', () => {
+  const name = [{ language: 'en', text: 'Republic Square' }];
+  for (const version of [undefined, '2.3', '3.0', '3.1', 'unknown']) {
+    assert.equal(parseName({ name }, version), 'Republic Square');
+    assert.equal(parseName({ name: 'Legacy name' }, version), 'Legacy name');
+  }
+});
+
+test('bad names do not lose valid stations or their metadata', () => {
+  const information = parseStationInformation({
+    version: '3.0',
+    data: {
+      stations: [
+        station({ station_id: 'bad', name: [null, {}] }),
+        station({
+          station_id: 'short',
+          name: [],
+          short_name: [{ language: 'en', text: 'Short' }],
+        }),
+        station({
+          station_id: 'good',
+          name: [{ language: 'en', text: 'Republic Square' }],
+        }),
+      ],
+    },
+  });
+  assert.equal(information.size, 3);
+  assert.equal(information.get('bad').name, '');
+  assert.equal(information.get('short').name, 'Short');
+  assert.deepEqual(information.get('good'), {
+    stationId: 'good',
+    name: 'Republic Square',
+    lat: 30.2681,
+    lon: -97.7469,
+    capacity: 13,
+    isInstalled: true,
+    isRenting: true,
+    isReturning: true,
+  });
+});
+
+test('normalizing a localized name leaves the feed document unchanged', () => {
+  const payload = {
+    version: '3.0',
+    data: {
+      stations: [
+        station({
+          name: [
+            { language: 'hu', text: 'Magyar' },
+            { language: 'en', text: ' English ' },
+          ],
+        }),
+      ],
+    },
+  };
+  const original = structuredClone(payload);
+  parseStationInformation(payload);
+  assert.deepEqual(payload, original);
+});

src/testSupport/kartaViewFakes.mjs

@@ -0,0 +1,81 @@
+// DOM stand-ins for the KartaView viewer's tests (no browser in Node).
+
+/** A DOM element with what the viewer touches: children, events, attributes. */
+export function fakeElement(tag) {
+  const listeners = new Map();
+  const element = {
+    tagName: tag.toUpperCase(),
+    children: [],
+    parentNode: null,
+    style: {},
+    dataset: {},
+    attributes: {},
+    hidden: false,
+    disabled: false,
+    clientWidth: 400,
+    clientHeight: 250,
+    classList: {
+      values: new Set(),
+      add: (name) => element.classList.values.add(name),
+      remove: (name) => element.classList.values.delete(name),
+    },
+    append(...nodes) {
+      for (const node of nodes) {
+        node.parentNode = element;
+        element.children.push(node);
+      }
+    },
+    remove() {
+      const list = element.parentNode?.children;
+      if (list) list.splice(list.indexOf(element), 1);
+      element.parentNode = null;
+    },
+    replaceWith(next) {
+      const parent = element.parentNode;
+      if (!parent) return;
+      parent.children[parent.children.indexOf(element)] = next;
+      next.parentNode = parent;
+      next.ownerDocument = element.ownerDocument;
+      element.parentNode = null;
+    },
+    setAttribute: (name, value) => (element.attributes[name] = value),
+    removeAttribute: (name) => {
+      delete element.attributes[name];
+      if (name === 'src') element.src = '';
+    },
+    addEventListener: (type, handler) => listeners.set(type, handler),
+    removeEventListener: (type) => listeners.delete(type),
+    setPointerCapture() {},
+    /** Fire an event at the element's listener. */
+    fire(type, event = {}) {
+      return listeners.get(type)?.({
+        preventDefault() {
+          this.defaultPrevented = true;
+        },
+        stopPropagation() {},
+        ...event,
+      });
+    },
+  };
+  return element;
+}
+
+export function fakeHost() {
+  const doc = { createElement: (tag) => fakeElement(tag) };
+  const host = fakeElement('div');
+  host.ownerDocument = doc;
+  return host;
+}
+
+/**
+ * Wait, a macrotask at a time, until `condition` holds; false if it never
+ * does within `ticks`. A test asserting that something did not happen waits
+ * on a sign that the work is done instead of a fixed count of ticks.
+ */
+export async function until(condition, { ticks = 200 } = {}) {
+  for (let i = 0; i < ticks; i++) {
+    if (await condition()) return true;
+    await new Promise((resolve) => setTimeout(resolve, 0));
+  }
+  return Boolean(await condition());
+}

src/testSupport/streetLevelFakes.mjs

@@ -1,6 +1,11 @@
 /** Shared Street Level test stand-ins: provider snapshot, minimal provider, ray-casting camera. */
 import * as Cesium from 'cesium';
 import { MAPILLARY_CREDIT_HTML } from '../layers/streetLevel/providers/mapillary/policy.js';
+import {
+  latToTileY,
+  lonToTileX,
+  tileBounds,
+} from '../layers/streetLevel/tileMath.js';
 
 const RAD = Math.PI / 180;
 
@@ -141,3 +146,92 @@ export function rayCamera({
     computeViewRectangle: () => undefined,
   };
 }
+
+/** The centre of the tile holding a point at zoom `z`, so a small view is one tile. */
+export function tileCentre(lon, lat, z = 14) {
+  const x = lonToTileX(lon, z);
+  const y = latToTileY(lat, z);
+  const { west, east, south, north } = tileBounds(x, y, z);
+  return {
+    tile: { x, y, z },
+    lon: (west + east) / 2,
+    lat: (south + north) / 2,
+  };
+}
+
+/** A scene collection that remembers what is on the globe. */
+function sceneCollection() {
+  const items = new Set();
+  return {
+    items,
+    add(primitive) {
+      items.add(primitive);
+      return primitive;
+    },
+    remove(primitive) {
+      return items.delete(primitive);
+    },
+  };
+}
+
+/**
+ * A viewer looking straight down on a 0.004° square around `view`
+ * (`{lon, lat, height}`, mutable), enough for line coverage to attach,
+ * refresh and draw. Cesium's one-time terrain-height download is skipped.
+ */
+export function coverageViewer(view, t) {
+  const initialize = Cesium.GroundPolylinePrimitive.initializeTerrainHeights;
+  Cesium.GroundPolylinePrimitive.initializeTerrainHeights = () =>
+    Promise.resolve();
+  t?.after(() => {
+    Cesium.GroundPolylinePrimitive.initializeTerrainHeights = initialize;
+  });
+  // Node has no WebGL context to report line-width limits.
+  Cesium.ContextLimits._minimumAliasedLineWidth = 1;
+  Cesium.ContextLimits._maximumAliasedLineWidth = 10;
+  const listeners = () => {
+    const set = new Set();
+    return {
+      set,
+      addEventListener(listener) {
+        set.add(listener);
+        return () => set.delete(listener);
+      },
+    };
+  };
+  return {
+    view,
+    scene: {
+      canvas: { clientWidth: 100, clientHeight: 100 },
+      globe: { show: false, ellipsoid: Cesium.Ellipsoid.WGS84 },
+      frameState: { mode: Cesium.SceneMode.SCENE3D },
+      updateHeight: () => () => {},
+      getHeight: () => undefined,
+      groundPrimitives: sceneCollection(),
+      primitives: sceneCollection(),
+      postRender: listeners(),
+      preRender: listeners(),
+    },
+    camera: {
+      changed: new Cesium.Event(),
+      moveEnd: new Cesium.Event(),
+      get positionWC() {
+        return Cesium.Cartesian3.fromDegrees(view.lon, view.lat, view.height);
+      },
+      get positionCartographic() {
+        return {
+          longitude: view.lon * RAD,
+          latitude: view.lat * RAD,
+          height: view.height,
+        };
+      },
+      pickEllipsoid(point) {
+        return Cesium.Cartesian3.fromDegrees(
+          view.lon - 0.002 + (point.x / 100) * 0.004,
+          view.lat + 0.002 - (point.y / 100) * 0.004,
+        );
+      },
+      computeViewRectangle: () => undefined,
+    },
+  };
+}

src/tooling/streetLevelQa.test.mjs

@@ -1,6 +1,7 @@
 import assert from 'node:assert/strict';
 import fs from 'node:fs';
 import test from 'node:test';
+import { inflateSync } from 'node:zlib';
 import { createApplicationStreetLevel } from '../app/layers/streetLevel.js';
 import {
   fixtureTile,
@@ -20,6 +21,24 @@ import {
   THUMB_HOST,
 } from '../../scripts/fixtures/street-level/mapillaryGraph.mjs';
 import { redact } from '../../scripts/qa-browserEvidence.mjs';
+import {
+  answerKartaViewRequest,
+  describeKartaViewCall,
+  KV_LINE,
+  KV_OLD_STREET,
+  KV_SEQUENCE_ID,
+  kartaViewPhotos,
+  resetKartaViewFixture,
+} from '../../scripts/fixtures/street-level/kartaView.mjs';
+import {
+  maskedSegments,
+  tileSegments,
+} from '../layers/streetLevel/providers/kartaview/decode.js';
+import { lonToTileX, latToTileY } from '../layers/streetLevel/tileMath.js';
+import {
+  normalizePhoto,
+  resizedImageUrl,
+} from '../layers/streetLevel/providers/kartaview/policy.js';
 
 // The press helpers wait for paint; Node has no frames, so a tick stands in.
 globalThis.requestAnimationFrame ??= (callback) =>
@@ -639,3 +658,170 @@ test('CI runs the gates hermetically against a production build, strict, with ev
     'a missed header press fails CI now that the rail settles',
   );
 });
+
+test('KartaView fixtures draw the drive, answer nearest first, and refuse the storage host the API names', () => {
+  const body = (answer) => JSON.parse(answer.body);
+  const lat = (KV_LINE.south + KV_LINE.north) / 2;
+  const x = lonToTileX(KV_LINE.lon, 14);
+  const y = latToTileY(lat, 14);
+  const tile = answerKartaViewRequest({
+    method: 'GET',
+    url: `https://api.kartaview.org/2.0/sequence/tiles/${x}/${y}/14.json`,
+  });
+  assert.equal(tile.known, true);
+  assert.ok(body(tile).lines.length >= 1);
+  const empty = answerKartaViewRequest({
+    method: 'GET',
+    url: `https://api.kartaview.org/2.0/sequence/tiles/${x + 3}/${y}/14.json`,
+  });
+  assert.deepEqual(body(empty).lines, []);
+  const nearUrl = `https://api.kartaview.org/2.0/photo/?lat=${lat}&lng=${KV_LINE.lon + 0.0001}&zoomLevel=18&itemsPerPage=10`;
+  resetKartaViewFixture();
+  // The first lookup is rate-limited, readable cross-origin; the retry answers.
+  const limited = answerKartaViewRequest({ method: 'GET', url: nearUrl });
+  assert.equal(limited.status, 429);
+  assert.equal(limited.known, true);
+  assert.equal(limited.headers['Retry-After'], '0');
+  assert.match(limited.headers['Access-Control-Expose-Headers'], /Retry-After/);
+  const near = answerKartaViewRequest({ method: 'GET', url: nearUrl });
+  assert.equal(near.status, 200);
+  const records = body(near).result.data;
+  assert.ok(records.length > 1);
+  assert.ok(Number(records[0].distance) <= Number(records[1].distance));
+  const photo = normalizePhoto(records[0]);
+  assert.match(photo.urls.view, /^https:\/\/storage2\.openstreetcam\.org\//);
+  assert.equal(
+    answerKartaViewRequest({ method: 'GET', url: photo.urls.view }).known,
+    true,
+  );
+  // Every odd photo is archived: its file answers 409, an even one the image.
+  const photos = kartaViewPhotos();
+  const storageAnswer = (index) =>
+    answerKartaViewRequest({
+      method: 'GET',
+      url: normalizePhoto(
+        body(
+          answerKartaViewRequest({
+            method: 'GET',
+            url: `https://api.kartaview.org/2.0/photo/${photos[index].id}`,
+          }),
+        ).result.data,
+      ).urls.view,
+    });
+  assert.equal(photos[3].archived, true);
+  assert.equal(storageAnswer(3).status, 409);
+  assert.equal(storageAnswer(3).known, true);
+  assert.equal(photos[4].archived, false);
+  assert.equal(storageAnswer(4).status, 200);
+  assert.equal(storageAnswer(4).contentType, 'image/jpeg');
+  // The image proxy still serves an archived photo: the 360° step opens one.
+  const pano = photos.find((p) => p.isPano);
+  assert.equal(pano.archived, true);
+  const panoRecord = body(
+    answerKartaViewRequest({
+      method: 'GET',
+      url: `https://api.kartaview.org/2.0/photo/${pano.id}`,
+    }),
+  ).result.data;
+  assert.equal(
+    answerKartaViewRequest({
+      method: 'GET',
+      url: resizedImageUrl(normalizePhoto(panoRecord).urls.pano, [1024, 512]),
+    }).status,
+    200,
+  );
+  assert.equal(
+    answerKartaViewRequest({ method: 'GET', url: records[0].fileurlLTh }).known,
+    false,
+    'the storage1 address the API gives is not where the photo is',
+  );
+  const page = answerKartaViewRequest({
+    method: 'GET',
+    url: `https://api.kartaview.org/2.0/sequence/${KV_SEQUENCE_ID}/photos?page=1&itemsPerPage=1000`,
+  });
+  assert.equal(body(page).result.data.length, kartaViewPhotos().length);
+  assert.ok(kartaViewPhotos().some((p) => p.isPano));
+  assert.equal(
+    describeKartaViewCall(
+      'GET',
+      new URL('https://api.kartaview.org/2.0/photo/77000001'),
+    ),
+    'GET api.kartaview.org/2.0/photo/{id}',
+  );
+});
+
+/** The alpha of a fixture PNG (8-bit RGBA, unfiltered rows, as it writes them). */
+function fixturePngAlpha(bytes) {
+  const width = bytes.readUInt32BE(16);
+  const height = bytes.readUInt32BE(20);
+  const idat = [];
+  for (let at = 8; at < bytes.length;) {
+    const length = bytes.readUInt32BE(at);
+    const type = bytes.toString('ascii', at + 4, at + 8);
+    if (type === 'IDAT') idat.push(bytes.subarray(at + 8, at + 8 + length));
+    at += 12 + length;
+  }
+  const rows = inflateSync(Buffer.concat(idat));
+  const alpha = new Uint8Array(width * height);
+  for (let y = 0; y < height; y++)
+    for (let x = 0; x < width; x++)
+      alpha[y * width + x] = rows[y * (width * 4 + 1) + 1 + x * 4 + 3];
+  return { width, height, alpha };
+}
+
+test('KartaView fixtures filter like KartaView: PNG tiles by view and upload date, the photo search by projection', () => {
+  const body = (answer) => JSON.parse(answer.body);
+  const z = 14;
+  const x = lonToTileX(KV_LINE.lon, z);
+  const y = latToTileY((KV_LINE.south + KV_LINE.north) / 2, z);
+  assert.equal(x, lonToTileX(KV_OLD_STREET.lon, z), 'both streets in a tile');
+  const base = `https://api.kartaview.org/2.0/sequence/tiles/${x}/${y}/${z}`;
+  const segments = tileSegments(
+    body(answerKartaViewRequest({ method: 'GET', url: `${base}.json` })),
+  );
+  const lons = (kept) => [...new Set(kept.map((segment) => segment[0][0]))];
+  const keptFor = (query) => {
+    const answer = answerKartaViewRequest({
+      method: 'GET',
+      url: `${base}.png?${query}`,
+    });
+    assert.equal(answer.contentType, 'image/png');
+    assert.equal(answer.known, true);
+    return lons(
+      maskedSegments(segments, fixturePngAlpha(answer.body), { x, y, z }),
+    );
+  };
+  assert.deepEqual(
+    lons(segments).sort(),
+    [KV_LINE.lon, KV_OLD_STREET.lon].sort(),
+  );
+  assert.deepEqual(keptFor('fieldOfView=360'), [KV_LINE.lon]);
+  assert.deepEqual(keptFor('fieldOfView=plane').sort(), lons(segments).sort());
+  const lastYear = new Date(Date.now() - 365 * 86_400_000)
+    .toISOString()
+    .slice(0, 10);
+  assert.deepEqual(keptFor(`startDate=${lastYear}`), [KV_LINE.lon]);
+  assert.deepEqual(keptFor('startDate=2099-01-01'), []);
+  assert.equal(
+    describeKartaViewCall('GET', new URL(`${base}.png?fieldOfView=360`)),
+    'GET api.kartaview.org/2.0/sequence/tiles/{x}/{y}/{z}.png?fieldOfView',
+  );
+  // The photo search: 360° only, and nothing uploaded after the drive.
+  resetKartaViewFixture();
+  const search = (extra) => {
+    answerKartaViewRequest({
+      method: 'GET',
+      url: 'https://api.kartaview.org/2.0/photo/?lat=0&lng=0',
+    });
+    return body(
+      answerKartaViewRequest({
+        method: 'GET',
+        url: `https://api.kartaview.org/2.0/photo/?lat=${KV_LINE.south + 0.002}&lng=${KV_LINE.lon}&zoomLevel=18&itemsPerPage=10${extra}`,
+      }),
+    ).result.data;
+  };
+  const panos = search('&projection=SPHERE');
+  assert.ok(panos.length > 0);
+  assert.ok(panos.every((record) => record.projection === 'SPHERE'));
+  assert.deepEqual(search('&startDate=2099-01-01'), []);
+});

src/tooling/transitQa.test.mjs

@@ -675,7 +675,7 @@ test('public transit documentation uses courtesy attribution and the approved gr
   );
   assert.ok(
     readme.includes(
-      'Twenty layers and map sources. **Seventeen have a keyless path.**',
+      'Twenty layers and map sources. **Eighteen have a keyless path.**',
     ),
   );
   assert.ok(

src/tools/globePanel.js

@@ -15,7 +15,8 @@ export const PANEL_WORKER_PRELUDE_PATH = 'cesium/worker-prelude.js';
 /**
  * Sites the app's browser code loads from directly: map imagery, 3D tiles,
  * terrain, fonts, and Street Level's Mapillary Graph API and image CDN (its
- * coverage tiles come through the app's server). Everything from the app's
+ * coverage tiles come through the app's server), Google Street View and
+ * KartaView. Everything from the app's
  * own server comes through the MCP server.
  */
 const PROVIDER_ORIGINS = Object.freeze([
@@ -44,6 +45,10 @@ const PROVIDER_ORIGINS = Object.freeze([
   'https://*.ggpht.com',
   // Mapillary photos come from regional hosts, e.g. scontent-man2-1.xx.fbcdn.net.
   'https://*.xx.fbcdn.net',
+  // KartaView's API, its image proxy and its photo storage (storage1…storage13).
+  'https://api.kartaview.org',
+  'https://cdn.kartaview.org',
+  'https://*.openstreetcam.org',
 ]);
 
 export const MCP_APP_MIME_TYPE = 'text/html;profile=mcp-app';

src/tools/queries/mobility.test.mjs

@@ -106,6 +106,34 @@ test('bike share joins station information with live status inside the area', as
   assert.equal(result.data.rows[1].capacity, 10);
 });
 
+test('bike share returns localized names without losing stations with malformed names', async () => {
+  const informationUrl = 'https://gbfs.example/austin/station_information.json';
+  const information = structuredClone(documents[informationUrl]);
+  information.version = '3.0';
+  information.data.stations[0].name = [
+    { language: 'hu', text: 'Magyar név' },
+    { language: 'en', text: 'Congress & 2nd' },
+  ];
+  information.data.stations[2].name = [null, { language: 42, text: [] }];
+  const source = bikeshare([system('austin', 'Austin, TX', 30.27, -97.74)]);
+  const catalog = composeCatalog({
+    tools: coreTools,
+    services: {
+      bikeshare: {
+        ...source,
+        getStations: (url) =>
+          url === informationUrl ? information : source.getStations(url),
+      },
+    },
+  });
+  const result = await catalog.call('get_bike_share', { area: downtown });
+  assert.equal(result.data.total, 2);
+  assert.equal(result.data.rows[0].name, 'Congress & 2nd');
+  assert.equal(result.data.rows[0].bikes_available, 4);
+  assert.equal(result.data.rows[1].name, null);
+  assert.doesNotMatch(result.summary, /unavailable/);
+});
+
 test('bike share reports uncovered areas and failed systems honestly', async () => {
   const none = composeCatalog({
     tools: coreTools,

src/ui/streetLevelControls.js

@@ -73,6 +73,7 @@ export class StreetLevelControls {
       sinceRow: byId('sl-since-row'),
       sinceRange: byId('sl-since'),
       sinceLabel: byId('sl-since-label'),
+      sinceNote: byId('sl-since-note'),
       legend: byId('sl-legend'),
       followBtn: byId('sl-follow-btn'),
       viewerWrap: byId('sl-viewer-wrap'),
@@ -527,6 +528,9 @@ export class StreetLevelControls {
     const shows = view.filterControls || { pano: true, since: true };
     setProp(el.panoRow, 'hidden', !shows.pano);
     setProp(el.sinceRow, 'hidden', !shows.since);
+    // A lit source that dates by upload says so under the slider.
+    setProp(el.sinceNote, 'textContent', view.sinceNote || '');
+    setProp(el.sinceNote, 'hidden', !view.sinceNote);
     setProp(el.controls, 'hidden', !shows.pano && !shows.since);
     setProp(el.legend, 'hidden', view.legend.length === 0);
     this._renderRadios(

src/ui/streetLevelControls.test.mjs

@@ -1,4 +1,5 @@
 import assert from 'node:assert/strict';
+import fs from 'node:fs';
 import test from 'node:test';
 import { StreetLevelControls } from './streetLevelControls.js';
 import { createStreetLevelLayer } from '../layers/streetLevel/index.js';
@@ -313,6 +314,7 @@ function panelDom() {
   const sinceRow = add(controls, 'div', { id: 'sl-since-row' });
   add(sinceRow, 'input', { id: 'sl-since' });
   add(sinceRow, 'output', { id: 'sl-since-label' });
+  add(sinceRow, 'small', { id: 'sl-since-note' });
   add(settings, 'ul', { id: 'sl-legend' });
   const metaRow = add(settings, 'div', { classes: ['sl-meta-row'] });
   add(metaRow, 'div', { id: 'sl-coverage-meta' });
@@ -1224,6 +1226,26 @@ test('a swap names every registered provider, also those hidden on this map', ()
     ]);
   }));
 
+test('a note under SINCE says what date it compares, only while one is given', () =>
+  withDom(async (dom) => {
+    const state = uiState();
+    const { layer } = stubPanel(dom, state);
+    const note = () => dom.root.querySelector('#sl-since-note');
+    assert.equal(note().hidden, true, 'none for Mapillary');
+    layer.publish({ ...state, sinceNote: 'KartaView: by upload date' });
+    assert.equal(note().hidden, false);
+    assert.equal(note().textContent, 'KartaView: by upload date');
+    layer.publish(state);
+    assert.equal(note().hidden, true);
+    // The panel's own markup has it, read out with the slider.
+    const template = fs.readFileSync(
+      new URL('./templates/layer-panels.html', import.meta.url),
+      'utf8',
+    );
+    assert.match(template, /<small id="sl-since-note"[^>]* hidden>/);
+    assert.match(template, /aria-describedby="sl-since-label sl-since-note"/);
+  }));
+
 test('Street View lit hides the imagery filters and the legend; Mapillary lit shows them', () =>
   withDom(async (dom) => {
     const state = uiState();

src/ui/streetLevelPresentation.js

@@ -193,7 +193,7 @@ function presentMeta(state) {
   const hint = state.coverage.hint || '';
   if (state.coverage.count > 0)
     return [
-      `${state.coverage.count.toLocaleString()} sequences in view · click a line for its photos`,
+      `${state.coverage.count.toLocaleString()} ${state.coverage.label?.noun || 'sequences'} in view · ${state.coverage.label?.action || 'click a line for its photos'}`,
       hint,
     ]
       .filter(Boolean)
@@ -224,6 +224,7 @@ export function presentStreetLevelPanel(state, { now = Date.now() } = {}) {
       since: state.filterControls?.since !== false,
     },
     since: presentSince(filter.sinceDays, now),
+    sinceNote: state.sinceNote || null,
     legend: state.legend || [],
     viewer: presentViewer(state),
     meta: presentMeta(state),

src/ui/styles/street-level.css

@@ -4,6 +4,9 @@
 #street-level-panel,
 .sl-viewer-wrap {
   --sl-green: #05cb63;
+  /* KartaView's purple for lines; a lighter one where it is text (WCAG AA). */
+  --sl-kartaview: #635bff;
+  --sl-kartaview-text: #8f8aff;
   --sl-text: 0.62rem;
   --sl-text-small: 0.6rem;
 }
@@ -174,6 +177,11 @@ button.sl-status:focus-visible {
   );
 }
 
+/* #635bff text on its own tint is 3.7:1 at this size; the lighter one is ~6:1. */
+.sl-chips .data-toggle-chip.active[data-chip-id='kartaview'] {
+  color: var(--sl-kartaview-text);
+}
+
 .sl-chips .data-toggle-chip.active::before {
   opacity: 1;
 }
@@ -291,6 +299,17 @@ button.sl-status:focus-visible {
   outline-offset: 3px;
 }
 
+.sl-since-note {
+  grid-column: 2;
+  font-family: var(--font-mono);
+  font-size: var(--sl-text-small);
+  color: var(--text-secondary);
+}
+
+.sl-since-note[hidden] {
+  display: none;
+}
+
 .sl-since-label {
   grid-column: 2;
   font-family: var(--font-mono);
@@ -613,6 +632,97 @@ button.sl-status:focus-visible {
   font-size: 1.3rem;
 }
 
+/* ── KartaView photo viewer ──────────────────────────────────────────────── */
+.sl-kv-viewer {
+  position: absolute;
+  inset: 0;
+  background: #000;
+  outline: none;
+  overflow: hidden;
+}
+
+.sl-kv-viewer:focus-visible {
+  outline: none;
+}
+
+/* The photo and canvas fill the viewer and would cover a ring drawn on it:
+   draw the ring on a layer above them (clicks pass through). */
+.sl-kv-viewer:focus-visible::after {
+  content: '';
+  position: absolute;
+  inset: 0;
+  z-index: 3;
+  border: 2px solid var(--sl-kartaview-text);
+  pointer-events: none;
+}
+
+.sl-kv-photo,
+.sl-kv-pano {
+  position: absolute;
+  inset: 0;
+  width: 100%;
+  height: 100%;
+  user-select: none;
+}
+
+.sl-kv-photo {
+  object-fit: contain;
+}
+
+.sl-kv-pano {
+  cursor: grab;
+  touch-action: none;
+}
+
+.sl-kv-pano.sl-kv-dragging {
+  cursor: grabbing;
+}
+
+.sl-kv-photo[hidden],
+.sl-kv-pano[hidden] {
+  display: none;
+}
+
+.sl-kv-step {
+  position: absolute;
+  top: 50%;
+  z-index: 2;
+  width: 34px;
+  height: 44px;
+  margin-top: -22px;
+  border: 1px solid rgba(255, 255, 255, 0.18);
+  border-radius: 8px;
+  background: rgba(10, 10, 15, 0.62);
+  color: #fff;
+  font-size: 1.5rem;
+  line-height: 1;
+  cursor: pointer;
+}
+
+.sl-kv-step-prev {
+  left: 6px;
+}
+
+.sl-kv-step-next {
+  right: 6px;
+}
+
+.sl-kv-step:hover:not(:disabled),
+.sl-kv-step:focus-visible {
+  background: color-mix(in srgb, var(--sl-kartaview) 85%, transparent);
+  outline: none;
+}
+
+.sl-kv-step:disabled {
+  opacity: 0.3;
+  cursor: default;
+}
+
+/* Nothing to step through until a photo shows. */
+.sl-kv-viewer:not([data-kind='flat']):not([data-kind='pano']) .sl-kv-step {
+  display: none;
+}
+
 /* ── Short viewports ─────────────────────────────────────────────────────── */
 @media (max-height: 640px) {
   .street-level-panel-inner {

src/ui/templates/layer-panels.html

@@ -128,8 +128,9 @@
               </div>
               <div id="sl-since-row" class="sl-since">
                 <label class="cctv-summary-label" for="sl-since">SINCE</label>
-                <input id="sl-since" class="sl-range" type="range" min="0" max="8" step="1" value="0" aria-valuetext="ANY DATE" aria-describedby="sl-since-label" />
+                <input id="sl-since" class="sl-range" type="range" min="0" max="8" step="1" value="0" aria-valuetext="ANY DATE" aria-describedby="sl-since-label sl-since-note" />
                 <output id="sl-since-label" class="sl-since-label" for="sl-since">ANY DATE</output>
+                <small id="sl-since-note" class="sl-since-note" hidden></small>
               </div>
             </fieldset>
             <ul id="sl-legend" class="sl-legend" aria-label="Coverage colours"></ul>