Preserve custom Street Level provider switches in shared state

src/data/layerState.js

@@ -1,3 +1,4 @@
+import { normalizeProviderSwitches } from '../layers/streetLevel/providerSwitches.js';
 import reservationRows from './layerStateTokenReservations.json' with { type: 'json' };
 
 const VALID_DISPOSITIONS = new Set([
@@ -411,8 +412,16 @@ const OPTION_GROUPS = Object.freeze({
     booleanOption('viirs', 'v', false),
   ]),
   'street-level': Object.freeze([
-    // One switch per registered imagery provider (src/app/layers/streetLevel.js).
+    // Preserve the published Mapillary token; custom switches use stable IDs.
     booleanOption('mapillary', 'm', true),
+    Object.freeze({
+      key: 'providerSwitches',
+      token: 'r',
+      defaultValue: '',
+      normalize: normalizeProviderSwitches,
+      encode: normalizeProviderSwitches,
+      decode: normalizeProviderSwitches,
+    }),
     enumOption('pano', 'p', 'all', ['all', 'pano', 'flat'], {
       all: 'a',
       pano: 'p',

src/data/layerState.test.mjs

@@ -2660,12 +2660,14 @@ test('Street Level: every option round-trips through a share link and stored sta
   state.enabledLayerIds = ['street-level'];
   state.options['street-level'] = {
     mapillary: false,
+    providerSwitches: '',
     pano: 'flat',
     sinceDays: MAX_SINCE_DAYS,
   };
   const decoded = decodeLayerStateParams(new URLSearchParams(encode(state)));
   assert.deepEqual(decoded.options['street-level'], {
     mapillary: false,
+    providerSwitches: '',
     pano: 'flat',
     sinceDays: MAX_SINCE_DAYS,
   });
@@ -2693,6 +2695,7 @@ test('Street Level: the link codec accepts exactly the windows the filter keeps'
 test('Street Level: a link without the provider switch keeps Mapillary on', () => {
   assert.deepEqual(streetLevelOptions(''), {
     mapillary: true,
+    providerSwitches: '',
     pano: 'all',
     sinceDays: 0,
   });

src/data/layerStateTokenLedger.test.mjs

@@ -98,6 +98,17 @@ function withPublishedBase(
 }
 
 function writeCodecFixture(cwd, rows, entries) {
+  const providerCodec = path.join(
+    cwd,
+    'src/layers/streetLevel/providerSwitches.js',
+  );
+  mkdirSync(path.dirname(providerCodec), { recursive: true });
+  writeFileSync(
+    providerCodec,
+    readFileSync(
+      new URL('../layers/streetLevel/providerSwitches.js', import.meta.url),
+    ),
+  );
   const source = readFileSync(CODEC_SOURCE_PATH, 'utf8');
   const registryEnd = ']);\n\nexport const REGISTERED_LAYER_IDS';
   assert.equal(source.split(registryEnd).length, 2);