feat(street-level): provider contract with Mapillary as the first provider

Street Level is now a provider-neutral layer modelled on the iD editor's
photo overlay. The core owns what every imagery provider shares: the
enable state and a switch per provider, the imagery filter (360°/flat and
captured-since in relative days), one click handler routed by pick prefix,
one viewer host that mounts whichever provider's viewer adapter owns the
open image, the position marker, camera follow, one on-globe credit per
active provider, and share-link parameters (one bit per provider plus the
filter). Providers implement the contract in registry.js: coverage,
sequences, nearest-image lookup and a viewer adapter emitting a common
pose. Mapillary is the only registered provider; Google Street View,
KartaView and Panoramax slot in beside it.

Panel: a PROVIDERS chip row (one chip per registered provider, keyless
chips read as errors), relative-day SINCE options, a provider-neutral
caption whose link label follows the provider, and no vendor mark in the
header. The panel inner is a rail scroller like CCTV's.

Tests cover the registry, params codec, filter, pick router, UI-state
composition, the provider definition and coverage-tile decoding; the QA
harness switches the provider off and on and checks the filter.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

src/layers/streetLevel/uiState.test.mjs

@@ -0,0 +1,104 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { composeUIState } from './uiState.js';
+
+const provider = (overrides = {}) => ({
+  id: 'mapillary',
+  name: 'Mapillary',
+  label: 'MAPILLARY',
+  on: true,
+  configured: true,
+  keyRequired: false,
+  requiresKeyId: 'mapillary',
+  loading: false,
+  count: 10,
+  hint: '',
+  error: null,
+  legend: [{ key: 'recent', label: 'Recent', color: '#0f0' }],
+  ...overrides,
+});
+const base = {
+  enabled: true,
+  filter: { pano: 'all', sinceDays: 0 },
+  street: { open: false },
+  sequence: { selectedId: null, images: 0, loading: false },
+};
+
+test('counts add up across active providers only', () => {
+  const ui = composeUIState({
+    ...base,
+    providers: [
+      provider(),
+      provider({ id: 'panoramax', name: 'Panoramax', count: 5, on: false }),
+      provider({ id: 'kartaview', name: 'KartaView', count: 7, loading: true }),
+    ],
+  });
+  assert.equal(ui.coverage.count, 17);
+  assert.equal(ui.coverage.loading, true);
+});
+
+test('the layer is key-gated only when every switched-on provider lacks its key', () => {
+  const gated = composeUIState({
+    ...base,
+    providers: [provider({ keyRequired: true })],
+  });
+  assert.equal(gated.keyRequired, true);
+  const mixed = composeUIState({
+    ...base,
+    providers: [
+      provider({ keyRequired: true }),
+      provider({ id: 'panoramax', name: 'Panoramax', requiresKeyId: null }),
+    ],
+  });
+  assert.equal(mixed.keyRequired, false, 'a keyless provider still draws');
+  const offOnly = composeUIState({
+    ...base,
+    providers: [provider({ keyRequired: true, on: false })],
+  });
+  assert.equal(offOnly.keyRequired, false, 'nothing switched on to gate');
+});
+
+test('the legend lists active providers, prefixed once more than one is registered', () => {
+  const single = composeUIState({ ...base, providers: [provider()] });
+  assert.deepEqual(
+    single.legend.map((entry) => [entry.key, entry.label]),
+    [
+      ['mapillary:recent', 'Recent'],
+      ['selected', 'Selected'],
+    ],
+  );
+  const two = composeUIState({
+    ...base,
+    providers: [
+      provider(),
+      provider({
+        id: 'panoramax',
+        name: 'Panoramax',
+        on: false,
+        legend: [{ key: 'coverage', label: 'Coverage', color: '#00f' }],
+      }),
+    ],
+  });
+  assert.deepEqual(
+    two.legend.map((entry) => entry.label),
+    ['Mapillary Recent', 'Selected'],
+  );
+  assert.deepEqual(
+    composeUIState({ ...base, providers: [provider({ on: false })] }).legend,
+    [],
+  );
+});
+
+test('hint and error come from the first active provider that has one', () => {
+  const ui = composeUIState({
+    ...base,
+    providers: [
+      provider({ hint: '', error: null }),
+      provider({ id: 'b', name: 'B', hint: 'Look down', error: 'boom' }),
+    ],
+  });
+  assert.equal(ui.coverage.hint, 'Look down');
+  assert.equal(ui.coverage.error, 'boom');
+  assert.deepEqual(ui.filter, base.filter);
+  assert.notEqual(ui.filter, base.filter, 'snapshot copies the filter');
+});