Lazy-load recommendation indexes

tests/services/explore-data-lifecycle.test.mjs

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+import assert from "node:assert/strict";
+import test from "node:test";
+import ExploreDataService from "../../js/services/exploreDataService.js";
+
+test("ExploreDataService stays idle until a recommendation feed activates it", async () => {
+  const service = new ExploreDataService({
+    historyRefreshIntervalMs: 0,
+    idfRefreshIntervalMs: 0,
+  });
+  let historyRefreshes = 0;
+  let idfRefreshes = 0;
+  service.refreshWatchHistoryTagCounts = async () => {
+    historyRefreshes += 1;
+    return new Map();
+  };
+  service.refreshTagIdf = async () => {
+    idfRefreshes += 1;
+    return new Map();
+  };
+
+  await service.initialize();
+  assert.equal(historyRefreshes, 0);
+  assert.equal(idfRefreshes, 0);
+
+  service.queueWatchHistoryRefresh("note");
+  service.queueTagIdfRefresh("note");
+  await service.setActive(true);
+  assert.equal(historyRefreshes, 1, "dirty history is refreshed on activation");
+  assert.equal(idfRefreshes, 1, "dirty IDF is refreshed on activation");
+
+  await service.setActive(false);
+  service.queueTagIdfRefresh("inactive-note");
+  assert.equal(idfRefreshes, 1, "inactive feeds do not rebuild recommendation indexes");
+  service.destroy();
+});