fix: refcount StatsCache keys, keep registrations across config change, and tidy GPU/usage render paths

tests/stats-cache.test.ts

@@ -83,3 +83,26 @@ test("fetch failure keeps the last-known value", async () => {
   assert.equal(cache.get("a"), undefined);
   cache.unregister("a");
 });
+
+test("ref-counted register: a sibling unregister keeps the key active", async () => {
+  const calls = { count: 0 };
+  const cache = new StatsCache(cfg, stubFetch({ totalRequests: 5, totalInputTokens: 1, totalOutputTokens: 1, genP95: 1 }, calls), 10000, 30);
+  cache.register("all");
+  cache.register("all");
+  cache.unregister("all");
+  await flush();
+  assert.equal(cache.get("all")!.totalRequests, 5);
+  assert.equal(calls.count, 1);
+  cache.unregister("all");
+  assert.equal(cache.get("all"), undefined);
+});
+
+test("setConfig keeps registrations but clears cached values", async () => {
+  const cache = new StatsCache(cfg, async (_c, key) => ({ totalRequests: 5, totalInputTokens: 1, totalOutputTokens: 1, genP95: 1 }), 10000, 30);
+  cache.register("all");
+  await flush();
+  assert.equal(cache.get("all")!.totalRequests, 5);
+  cache.setConfig({ baseUrl: "http://new" });
+  assert.equal(cache.get("all"), undefined);
+  cache.unregister("all");
+});