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/lib/http.ts

@@ -0,0 +1,25 @@
+/** Minimal fetch helpers the dashboard store depends on. */
+
+export interface RequestOptions {
+  retries: number;
+  timeoutMs: number;
+}
+
+export const defaultRequestOptions: RequestOptions = { retries: 2, timeoutMs: 5_000 };
+
+/** Build a query string from a plain record, skipping empty values. */
+export function toQueryString(params: Record<string, string | number | undefined>): string {
+  const parts: string[] = [];
+  for (const [key, value] of Object.entries(params)) {
+    if (value === undefined || value === '') continue;
+    parts.push(`${encodeURIComponent(key)}=${encodeURIComponent(String(value))}`);
+  }
+  return parts.length > 0 ? `?${parts.join('&')}` : '';
+}
+
+/** Join a base path and a resource path without doubling the separator. */
+export function joinPath(base: string, resource: string): string {
+  if (base.endsWith('/') && resource.startsWith('/')) return base + resource.slice(1);
+  if (!base.endsWith('/') && !resource.startsWith('/')) return `${base}/${resource}`;
+  return base + resource;
+}

__tests__/fixtures/factory-closure-ts/src/lib/metrics.ts

@@ -0,0 +1,37 @@
+import type { MetricSample } from '../stores/types';
+
+/** Statistics helpers shared by the store and the panel. */
+
+export function meanOf(samples: readonly MetricSample[]): number {
+  if (samples.length === 0) return 0;
+  let total = 0;
+  for (const sample of samples) total += sample.value;
+  return total / samples.length;
+}
+
+export function medianOf(samples: readonly MetricSample[]): number {
+  if (samples.length === 0) return 0;
+  const values = samples.map((s) => s.value).sort((a, b) => a - b);
+  const mid = Math.floor(values.length / 2);
+  return values.length % 2 === 0 ? (values[mid - 1]! + values[mid]!) / 2 : values[mid]!;
+}
+
+export function rateOfChange(samples: readonly MetricSample[]): number {
+  if (samples.length < 2) return 0;
+  const ordered = samples.slice().sort((a, b) => a.at - b.at);
+  const first = ordered[0]!;
+  const last = ordered[ordered.length - 1]!;
+  const elapsed = last.at - first.at;
+  return elapsed > 0 ? (last.value - first.value) / elapsed : 0;
+}
+
+export function bucketByHour(samples: readonly MetricSample[]): Map<number, MetricSample[]> {
+  const buckets = new Map<number, MetricSample[]>();
+  for (const sample of samples) {
+    const hour = Math.floor(sample.at / 3_600_000);
+    const bucket = buckets.get(hour);
+    if (bucket) bucket.push(sample);
+    else buckets.set(hour, [sample]);
+  }
+  return buckets;
+}