test(explore): add the factory-closure fixture and its selection probe (CG-27)

A file whose top-level symbol spans almost all of it — createFoo() returning
an object of closures — is how Svelte 5 rune stores, React custom-hook modules,
IIFE module-pattern JS and Zustand's create((set,get)=>({…})) are all written.
probe-factory-closure.mjs measures what such a file DELIVERS from within: which
inner symbols' definitions reach the agent, not how many bytes did.

__tests__/fixtures/factory-closure-ts/src/index.ts

@@ -0,0 +1,23 @@
+import { createDashboardStore } from './stores/dashboard-store';
+import { createAlertsStore } from './stores/alerts-store';
+import { mountPanel } from './ui/panel';
+import { parseFilterText } from './services/filter-parser';
+import { refreshMetricCache } from './services/metric-service';
+import type { StoreDeps } from './stores/types';
+
+/** Wire a dashboard: build both stores, mount the panel, boot it. */
+export async function startDashboard(deps: StoreDeps, baseUrl: string, dashboardId: string) {
+  const store = createDashboardStore(deps, baseUrl);
+  const alerts = createAlertsStore(deps, baseUrl);
+  const panel = mountPanel(store, dashboardId);
+  await panel.boot();
+  await alerts.refreshAlerts(dashboardId);
+  return { store, alerts, panel };
+}
+
+/** Apply the filter bar's text to the dashboard store. */
+export function searchDashboard(store: ReturnType<typeof createDashboardStore>, text: string) {
+  return store.applyFilter(parseFilterText(text));
+}
+
+export { refreshMetricCache };