refactor: expose reference sources independently of standalone setup

src/sources/reference.js

@@ -0,0 +1,10 @@
+import { createUsgsEarthquakeSource } from '../layers/earthquakes/source.js';
+import { createBundledCableSource } from '../layers/submarineCables/bundledSource.js';
+
+/** Construct the existing reference feeds independently of application setup. */
+export function createReferenceSources() {
+  return {
+    earthquakes: createUsgsEarthquakeSource(),
+    cables: createBundledCableSource(),
+  };
+}

src/sources/reference.test.mjs

@@ -0,0 +1,21 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { createReferenceSources } from './reference.js';
+import { createStandaloneReferenceSources } from '../standalone/layerSources.js';
+
+test('reference factories retain compatibility without starting acquisition or sharing instances', (t) => {
+  let requests = 0;
+  t.mock.method(globalThis, 'fetch', () => {
+    requests++;
+    throw new Error('unexpected acquisition');
+  });
+  assert.equal(createReferenceSources, createStandaloneReferenceSources);
+  const first = createReferenceSources();
+  const second = createReferenceSources();
+  assert.deepEqual(Object.keys(first), ['earthquakes', 'cables']);
+  assert.notEqual(first.earthquakes, second.earthquakes);
+  assert.notEqual(first.cables, second.cables);
+  assert.equal(typeof first.earthquakes.getSnapshot, 'function');
+  assert.equal(typeof first.cables.fetch, 'function');
+  assert.equal(requests, 0);
+});