perf : improve via lighthouse

tests/public-performance.test.ts

@@ -0,0 +1,35 @@
+import { readFile } from "node:fs/promises";
+
+import { describe, expect, it } from "vitest";
+
+async function repositoryFile(path: string): Promise<string> {
+  return readFile(new URL(`../${path}`, import.meta.url), "utf8");
+}
+
+describe("public rendering performance", () => {
+  it("keeps the directory eligible for a populated static shell", async () => {
+    const [layout, page] = await Promise.all([
+      repositoryFile("app/layout.tsx"),
+      repositoryFile("app/page.tsx"),
+    ]);
+
+    expect(layout).not.toContain("export const instant = false");
+    expect(page).not.toContain("connection()");
+    expect(page).not.toContain("export const instant = false");
+  });
+
+  it("isolates request-time header authentication", async () => {
+    const header = await repositoryFile("components/public/site-header.tsx");
+
+    expect(header).toContain("<Suspense fallback={null}>");
+    expect(header).toContain("<AdminEditLink");
+  });
+
+  it("preloads only the first directory cover", async () => {
+    const directory = await repositoryFile(
+      "components/public/structured-directory.tsx",
+    );
+
+    expect(directory).toContain("preload={index === 0}");
+  });
+});