Layer state keeps only layers the application registered

An application built with fewer layers no longer restores, stores or shares a
layer it does not have when a link or saved state from a build that has it
names that layer. LayerStateCoordinator drops unregistered enabled-layer ids
before normalizing, so dependent options (a tracked selection) go with them.
An application with every layer registered is unchanged.

docs/CURRENT-STATE.md

@@ -5627,6 +5627,13 @@ and unreachable upstream (502/504) separately from road geometry.
   explicit-empty form); unknown option tokens are ignored. Restoration
   settles independently per layer so one failed or unavailable source cannot
   block its siblings.
+- An application that registers fewer layers (an embedder with a smaller
+  catalog) keeps only its own: `LayerStateCoordinator` drops enabled-layer ids
+  the application did not register before it normalizes a share, saved state or
+  explicit change, so such a layer is never restored, written to local storage
+  or carried into a link this application shares. Options that depend on a
+  dropped layer (a tracked selection) go with it. An application with every
+  layer registered is unchanged.
 - Layer tokens are permanent public compatibility identifiers. The reservation
   JSON ledger at `src/data/layerStateTokenReservations.json` pins all existing
   one-character assignments (all letters plus `0`, `1` and

src/data/layerState.test.mjs

@@ -3121,3 +3121,70 @@ test('Active Fires: the codec accepts whole megawatts in bounds and the three co
     confidence: 'nominal',
   });
 });
+
+// An application built without a layer (a smaller catalog) receives a link or
+// saved state from a build that has it: the layer is neither restored nor
+// stored nor carried into the links this application shares.
+function managerWithout(withheld) {
+  const manager = new DataLayerManager({});
+  for (const id of REGISTERED_LAYER_IDS)
+    if (!withheld.includes(id)) manager.register(fakeLayer(id));
+  manager.finalizeRegistrations(
+    LAYER_STATE_REGISTRY.filter(({ id }) => !withheld.includes(id)),
+  );
+  return manager;
+}
+
+test('layers the application did not register are never restored, stored or shared', async () => {
+  const manager = managerWithout(['earthquakes']);
+  const storage = memoryStorage();
+  const share = shareSink();
+  const coordinator = new LayerStateCoordinator(manager, share, { storage });
+  const incoming = createDefaultLayerState();
+  incoming.enabledLayerIds = ['earthquakes', 'traffic'];
+  await coordinator.start({ shareLayerState: incoming });
+
+  assert.deepEqual(coordinator.getDurableState().enabledLayerIds, ['traffic']);
+  assert.deepEqual(share.provider().enabledLayerIds, ['traffic']);
+  assert.equal(manager.layers.has('earthquakes'), false);
+
+  await manager.setEnabled('cctv', true, { origin: 'user' });
+  const [[, written]] = storage.writes;
+  assert.deepEqual(parseStoredLayerState(written).enabledLayerIds, [
+    'cctv',
+    'traffic',
+  ]);
+  assert.deepEqual(share.provider().enabledLayerIds, ['cctv', 'traffic']);
+
+  await coordinator.applyShareLayerState({ shareLayerState: incoming });
+  assert.deepEqual(coordinator.getDurableState().enabledLayerIds, ['traffic']);
+  coordinator.destroy();
+
+  const saved = createDefaultLayerState();
+  saved.enabledLayerIds = ['earthquakes', 'traffic'];
+  const local = new LayerStateCoordinator(
+    managerWithout(['earthquakes']),
+    shareSink(),
+    { storage: memoryStorage(serializeStoredLayerState(saved)) },
+  );
+  await local.start();
+  assert.equal(local.source, 'local');
+  assert.deepEqual(local.getDurableState().enabledLayerIds, ['traffic']);
+  local.destroy();
+});
+
+test('an application with every layer registered keeps every requested layer', async () => {
+  const coordinator = new LayerStateCoordinator(
+    productionManager(),
+    shareSink(),
+    { storage: memoryStorage() },
+  );
+  const incoming = createDefaultLayerState();
+  incoming.enabledLayerIds = ['earthquakes', 'traffic'];
+  await coordinator.start({ shareLayerState: incoming });
+  assert.deepEqual(coordinator.getDurableState().enabledLayerIds, [
+    'earthquakes',
+    'traffic',
+  ]);
+  coordinator.destroy();
+});

src/data/layerStateCoordinator.js

@@ -106,9 +106,7 @@ export class LayerStateCoordinator {
   } = {}) {
     if (this._destroyed)
       throw new Error('Layer-state coordinator is destroyed');
-    let selected = shareLayerState
+    let selected = shareLayerState ? this._normalize(shareLayerState) : null;
-      ? normalizeLayerState(shareLayerState)
-      : null;
     if (selected) {
       this._source = 'share';
       this._shareCreatedAtMs = Number.isFinite(shareCreatedAtMs)
@@ -124,7 +122,7 @@ export class LayerStateCoordinator {
         /* best effort */
       }
       if (stored) {
-        selected = stored;
+        selected = this._normalize(stored);
         this._source = 'local';
       }
     } else {
@@ -163,9 +161,7 @@ export class LayerStateCoordinator {
     for (const controller of this._restoreControllers.values())
       controller.abort('superseded-by-share-navigation');
     this._revokePendingTrackingWatch('superseded-by-share-navigation');
-    const selected = shareLayerState
+    const selected = shareLayerState ? this._normalize(shareLayerState) : null;
-      ? normalizeLayerState(shareLayerState)
-      : null;
     this._source = selected ? 'share' : 'legacy-share';
     this._shareCreatedAtMs =
       selected && Number.isFinite(shareCreatedAtMs) ? shareCreatedAtMs : null;
@@ -182,6 +178,25 @@ export class LayerStateCoordinator {
     return this._source;
   }
 
+  /**
+   * Canonical layer state holding only the layers this application
+   * registered. An application built without a layer never restores, stores
+   * or shares it, even when a link or saved state from a build that has it
+   * names it. Filtering before normalizing lets normalization drop options
+   * that depend on a layer that is not here (a tracked selection).
+   */
+  _normalize(candidate) {
+    const input = candidate && typeof candidate === 'object' ? candidate : {};
+    return normalizeLayerState({
+      ...input,
+      enabledLayerIds: Array.isArray(input.enabledLayerIds)
+        ? input.enabledLayerIds.filter((id) =>
+            this.dataManager.layers.has(String(id)),
+          )
+        : [],
+    });
+  }
+
   getDurableState() {
     return cloneLayerState(this._durableState);
   }
@@ -345,7 +360,7 @@ export class LayerStateCoordinator {
   }
 
   _commitExplicit(candidate) {
-    this._durableState = normalizeLayerState(candidate);
+    this._durableState = this._normalize(candidate);
     const serialized = serializeStoredLayerState(this._durableState);
     try {
       if (this.storage?.getItem?.(LAYER_STATE_STORAGE_KEY) !== serialized) {
@@ -478,7 +493,7 @@ export class LayerStateCoordinator {
       ...this._durableState.options[selected.optionOwner],
       [selected.optionKey]: null,
     };
-    this._durableState = normalizeLayerState({
+    this._durableState = this._normalize({
       ...this._durableState,
       options: {
         ...this._durableState.options,